Infection, Infectious Diseases and epidemiology
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Chapter 14:Chapter 14:
Infection, Infectious Diseases and Infection, Infectious Diseases and
EpidemiologyEpidemiology
Infection, Infectious Diseases and Infection, Infectious Diseases and
EpidemiologyEpidemiology
IntroductionIntroduction
PathologyPathology is the scientific study of disease. is the scientific study of disease.
EtiologyEtiology: Cause of disease.: Cause of disease.
PathogenesisPathogenesis: Studies how disease develops.: Studies how disease develops.
InfectionInfection: Invasion or colonization of the body : Invasion or colonization of the body
by pathogenic organisms.by pathogenic organisms.
DiseaseDisease: Occurs when an infection results in a : Occurs when an infection results in a
change from a state of health.change from a state of health.
PathologyPathology is the scientific study of disease. is the scientific study of disease.
EtiologyEtiology: Cause of disease.: Cause of disease.
PathogenesisPathogenesis: Studies how disease develops.: Studies how disease develops.
InfectionInfection: Invasion or colonization of the body : Invasion or colonization of the body
by pathogenic organisms.by pathogenic organisms.
DiseaseDisease: Occurs when an infection results in a : Occurs when an infection results in a
change from a state of health.change from a state of health.
Normal MicrobiotaNormal Microbiota
Animals are generally free from microbes in utero.Animals are generally free from microbes in utero.
After birth, microbial populations rapidly establish After birth, microbial populations rapidly establish
themselves in the newborn’s body.themselves in the newborn’s body.
Vaginal lactobacilli colonize newborn’s intestine.Vaginal lactobacilli colonize newborn’s intestine.
Feeding and breathing introduce many more microbes.Feeding and breathing introduce many more microbes.
E. coliE. coli and other bacteria colonize large intestine. and other bacteria colonize large intestine.
Candida albicansCandida albicans colonizes mucous membranes. colonizes mucous membranes.
Normal Microbiota or FloraNormal Microbiota or Flora: Microorganisms that : Microorganisms that
remain throughout an individual’s life.remain throughout an individual’s life.
Transient MicrobiotaTransient Microbiota: Microorganisms that are present : Microorganisms that are present
for a certain time period and then disappear. for a certain time period and then disappear.
Cells in human body: Cells in human body: 1 x 101 x 10
1313
Microbes associated with human body: Microbes associated with human body: 1 x 101 x 10
1414
There are ~10 microorganisms/human body cell.There are ~10 microorganisms/human body cell.
Animals are generally free from microbes in utero.Animals are generally free from microbes in utero.
After birth, microbial populations rapidly establish After birth, microbial populations rapidly establish
themselves in the newborn’s body.themselves in the newborn’s body.
Vaginal lactobacilli colonize newborn’s intestine.Vaginal lactobacilli colonize newborn’s intestine.
Feeding and breathing introduce many more microbes.Feeding and breathing introduce many more microbes.
E. coliE. coli and other bacteria colonize large intestine. and other bacteria colonize large intestine.
Candida albicansCandida albicans colonizes mucous membranes. colonizes mucous membranes.
Normal Microbiota or FloraNormal Microbiota or Flora: Microorganisms that : Microorganisms that
remain throughout an individual’s life.remain throughout an individual’s life.
Transient MicrobiotaTransient Microbiota: Microorganisms that are present : Microorganisms that are present
for a certain time period and then disappear. for a certain time period and then disappear.
Cells in human body: Cells in human body: 1 x 101 x 10
1313
Microbes associated with human body: Microbes associated with human body: 1 x 101 x 10
1414
There are ~10 microorganisms/human body cell.There are ~10 microorganisms/human body cell.
Normal Microbiota of the Body
Skin BacteriaGum plaque Intestinal Flora
Skin BacteriaGum plaque Intestinal Flora
Location of Normal Microbiota
Relationships Between the Normal Relationships Between the Normal
Microbiota and the HostMicrobiota and the Host
Microbial AntagonismMicrobial Antagonism: Normal flora inhibits : Normal flora inhibits
overgrowth of harmful microbes. overgrowth of harmful microbes.
Mechanisms include competition for nutrients Mechanisms include competition for nutrients
and affecting environmental factors such as pH, and affecting environmental factors such as pH,
toxic substances, and oxygen availability.toxic substances, and oxygen availability.
Vaginal flora maintains pH of 3.5-4.5 which inhibits Vaginal flora maintains pH of 3.5-4.5 which inhibits
overgrowth of overgrowth of Candida albicansCandida albicans..
In mouth streptococci produce compounds that inhibit In mouth streptococci produce compounds that inhibit
growth of many other cocci.growth of many other cocci.
In intestine In intestine E. coliE. coli produce produce bacteriocinsbacteriocins, which inhibit , which inhibit
growth of closely related bacteria.growth of closely related bacteria.
C. dificileC. dificile is inhibited by normal intestinal flora. is inhibited by normal intestinal flora.
Microbiota and the HostMicrobiota and the Host
Microbial AntagonismMicrobial Antagonism: Normal flora inhibits : Normal flora inhibits
overgrowth of harmful microbes. overgrowth of harmful microbes.
Mechanisms include competition for nutrients Mechanisms include competition for nutrients
and affecting environmental factors such as pH, and affecting environmental factors such as pH,
toxic substances, and oxygen availability.toxic substances, and oxygen availability.
Vaginal flora maintains pH of 3.5-4.5 which inhibits Vaginal flora maintains pH of 3.5-4.5 which inhibits
overgrowth of overgrowth of Candida albicansCandida albicans..
In mouth streptococci produce compounds that inhibit In mouth streptococci produce compounds that inhibit
growth of many other cocci.growth of many other cocci.
In intestine In intestine E. coliE. coli produce produce bacteriocinsbacteriocins, which inhibit , which inhibit
growth of closely related bacteria.growth of closely related bacteria.
C. dificileC. dificile is inhibited by normal intestinal flora. is inhibited by normal intestinal flora.
Relationships Between the Normal Relationships Between the Normal
Microbiota and the HostMicrobiota and the Host
SYMBIOSISSYMBIOSIS: “Living together”. Relationship : “Living together”. Relationship
between the host and its normal flora.between the host and its normal flora.
1. Commensalism1. Commensalism: One organism benefits, the : One organism benefits, the
other is not affected (+/0). other is not affected (+/0).
Many microbes live off secretions and dead cells and Many microbes live off secretions and dead cells and
do not benefit or harm host.do not benefit or harm host.
2. Mutualism2. Mutualism: Both organisms benefit from living : Both organisms benefit from living
together (+/+).together (+/+).
E. coli synthesizes vitamin K and some B vitamins.E. coli synthesizes vitamin K and some B vitamins.
3. Parasitism3. Parasitism: One organism benefits, the other is : One organism benefits, the other is
harmed (+/-). harmed (+/-).
Most disease causing bacteria.Most disease causing bacteria.
Microbiota and the HostMicrobiota and the Host
SYMBIOSISSYMBIOSIS: “Living together”. Relationship : “Living together”. Relationship
between the host and its normal flora.between the host and its normal flora.
1. Commensalism1. Commensalism: One organism benefits, the : One organism benefits, the
other is not affected (+/0). other is not affected (+/0).
Many microbes live off secretions and dead cells and Many microbes live off secretions and dead cells and
do not benefit or harm host.do not benefit or harm host.
2. Mutualism2. Mutualism: Both organisms benefit from living : Both organisms benefit from living
together (+/+).together (+/+).
E. coli synthesizes vitamin K and some B vitamins.E. coli synthesizes vitamin K and some B vitamins.
3. Parasitism3. Parasitism: One organism benefits, the other is : One organism benefits, the other is
harmed (+/-). harmed (+/-).
Most disease causing bacteria.Most disease causing bacteria.
Opportunistic PathogensOpportunistic Pathogens
The nature of symbiotic relationships can change.The nature of symbiotic relationships can change.
Opportunistic PathogensOpportunistic Pathogens: Organisms that : Organisms that
normally do not cause disease in their natural normally do not cause disease in their natural
habitat in a healthy person. They may cause habitat in a healthy person. They may cause
disease if the host is weakened or if they enter a disease if the host is weakened or if they enter a
different part of the body.different part of the body.
Pneumocystis cariniiPneumocystis carinii pneumonia in AIDS patients. pneumonia in AIDS patients.
Tooth decay and gum disease caused by mouth flora.Tooth decay and gum disease caused by mouth flora.
Neisseria meningitidisNeisseria meningitidis is usually harmless in is usually harmless in
respiratory tract, but can cause meningitis.respiratory tract, but can cause meningitis.
E. coliE. coli can cause urinary tract infections, meningitis, can cause urinary tract infections, meningitis,
pneumonia, and abscesses.pneumonia, and abscesses.
The nature of symbiotic relationships can change.The nature of symbiotic relationships can change.
Opportunistic PathogensOpportunistic Pathogens: Organisms that : Organisms that
normally do not cause disease in their natural normally do not cause disease in their natural
habitat in a healthy person. They may cause habitat in a healthy person. They may cause
disease if the host is weakened or if they enter a disease if the host is weakened or if they enter a
different part of the body.different part of the body.
Pneumocystis cariniiPneumocystis carinii pneumonia in AIDS patients. pneumonia in AIDS patients.
Tooth decay and gum disease caused by mouth flora.Tooth decay and gum disease caused by mouth flora.
Neisseria meningitidisNeisseria meningitidis is usually harmless in is usually harmless in
respiratory tract, but can cause meningitis.respiratory tract, but can cause meningitis.
E. coliE. coli can cause urinary tract infections, meningitis, can cause urinary tract infections, meningitis,
pneumonia, and abscesses.pneumonia, and abscesses.
Cooperation Among MicrobesCooperation Among Microbes
SynergismSynergism: The effect of two microbes acting : The effect of two microbes acting
together, is greater than the effect of either acting together, is greater than the effect of either acting
alone.alone.
HIV and mycoplasma infection: Cells infected with HIV and mycoplasma infection: Cells infected with
mycoplasma and HIV die more readily than those infected mycoplasma and HIV die more readily than those infected
with mycoplasma alone.with mycoplasma alone.
HIV and Oncogenic Viruses: HIV and Oncogenic Viruses:
Women with HIV infections develop very aggressive cervical Women with HIV infections develop very aggressive cervical
cancers which are caused by papillomavirus.cancers which are caused by papillomavirus.
Individuals with HIV and Human Herpes Virus 8 infections, are Individuals with HIV and Human Herpes Virus 8 infections, are
more likely to develop Kaposi’s sarcoma.more likely to develop Kaposi’s sarcoma.
Oral streptococci and pathogens that cause gingivitis and Oral streptococci and pathogens that cause gingivitis and
periodontal disease. Pathogens bind to streptococci periodontal disease. Pathogens bind to streptococci
instead of host tissue.instead of host tissue.
SynergismSynergism: The effect of two microbes acting : The effect of two microbes acting
together, is greater than the effect of either acting together, is greater than the effect of either acting
alone.alone.
HIV and mycoplasma infection: Cells infected with HIV and mycoplasma infection: Cells infected with
mycoplasma and HIV die more readily than those infected mycoplasma and HIV die more readily than those infected
with mycoplasma alone.with mycoplasma alone.
HIV and Oncogenic Viruses: HIV and Oncogenic Viruses:
Women with HIV infections develop very aggressive cervical Women with HIV infections develop very aggressive cervical
cancers which are caused by papillomavirus.cancers which are caused by papillomavirus.
Individuals with HIV and Human Herpes Virus 8 infections, are Individuals with HIV and Human Herpes Virus 8 infections, are
more likely to develop Kaposi’s sarcoma.more likely to develop Kaposi’s sarcoma.
Oral streptococci and pathogens that cause gingivitis and Oral streptococci and pathogens that cause gingivitis and
periodontal disease. Pathogens bind to streptococci periodontal disease. Pathogens bind to streptococci
instead of host tissue.instead of host tissue.
Etiology of Infectious DiseasesEtiology of Infectious Diseases
Diseases can be caused by many factors: infection, Diseases can be caused by many factors: infection,
genetics, degeneration, and others.genetics, degeneration, and others.
Koch’s PostulatesKoch’s Postulates
Developed by Robert Koch in 1877 to establish Developed by Robert Koch in 1877 to establish
cause of infectious diseases: anthrax and TB. cause of infectious diseases: anthrax and TB.
1. Same pathogen must be present in every case of the 1. Same pathogen must be present in every case of the
disease.disease.
2. Pathogen must be isolated from diseased host and grown 2. Pathogen must be isolated from diseased host and grown
in pure culture.in pure culture.
3. Pathogen from pure culture must cause disease when 3. Pathogen from pure culture must cause disease when
inoculated in healthy, susceptible laboratory animal.inoculated in healthy, susceptible laboratory animal.
4. Pathogen must be isolated from inoculated animal and 4. Pathogen must be isolated from inoculated animal and
shown to be the original organism.shown to be the original organism.
Diseases can be caused by many factors: infection, Diseases can be caused by many factors: infection,
genetics, degeneration, and others.genetics, degeneration, and others.
Koch’s PostulatesKoch’s Postulates
Developed by Robert Koch in 1877 to establish Developed by Robert Koch in 1877 to establish
cause of infectious diseases: anthrax and TB. cause of infectious diseases: anthrax and TB.
1. Same pathogen must be present in every case of the 1. Same pathogen must be present in every case of the
disease.disease.
2. Pathogen must be isolated from diseased host and grown 2. Pathogen must be isolated from diseased host and grown
in pure culture.in pure culture.
3. Pathogen from pure culture must cause disease when 3. Pathogen from pure culture must cause disease when
inoculated in healthy, susceptible laboratory animal.inoculated in healthy, susceptible laboratory animal.
4. Pathogen must be isolated from inoculated animal and 4. Pathogen must be isolated from inoculated animal and
shown to be the original organism.shown to be the original organism.
Koch’s Postulates for Infectious Diseases
Exceptions to Koch’s PostulatesExceptions to Koch’s Postulates
Koch’s principles do not apply to all diseases. Koch’s principles do not apply to all diseases.
1. Some microbes cannot be cultured in artificial media.1. Some microbes cannot be cultured in artificial media.
Treponema pallidumTreponema pallidum (syphillis) (syphillis)
Mycobacterium lepraeMycobacterium leprae (leprosy) (leprosy)
Ricketsias, chlamydias, and viruses only multiply within cells.Ricketsias, chlamydias, and viruses only multiply within cells.
2. One disease may involve several different pathogens.2. One disease may involve several different pathogens.
DiarrheaDiarrhea
PneumoniaPneumonia
MeningitisMeningitis
PeritonitisPeritonitis
NephritisNephritis
3. Some pathogens may cause several different diseases.3. Some pathogens may cause several different diseases.
Streptococcus pyogenesStreptococcus pyogenes: Scarlet fever, sore throat, skin infections, : Scarlet fever, sore throat, skin infections,
bone infections, etc.bone infections, etc.
Mycobacterium tuberculosisMycobacterium tuberculosis: Causes disease of lungs, skin, bones, and : Causes disease of lungs, skin, bones, and
internal organs.internal organs.
Koch’s principles do not apply to all diseases. Koch’s principles do not apply to all diseases.
1. Some microbes cannot be cultured in artificial media.1. Some microbes cannot be cultured in artificial media.
Treponema pallidumTreponema pallidum (syphillis) (syphillis)
Mycobacterium lepraeMycobacterium leprae (leprosy) (leprosy)
Ricketsias, chlamydias, and viruses only multiply within cells.Ricketsias, chlamydias, and viruses only multiply within cells.
2. One disease may involve several different pathogens.2. One disease may involve several different pathogens.
DiarrheaDiarrhea
PneumoniaPneumonia
MeningitisMeningitis
PeritonitisPeritonitis
NephritisNephritis
3. Some pathogens may cause several different diseases.3. Some pathogens may cause several different diseases.
Streptococcus pyogenesStreptococcus pyogenes: Scarlet fever, sore throat, skin infections, : Scarlet fever, sore throat, skin infections,
bone infections, etc.bone infections, etc.
Mycobacterium tuberculosisMycobacterium tuberculosis: Causes disease of lungs, skin, bones, and : Causes disease of lungs, skin, bones, and
internal organs.internal organs.
Effects of Infectious Diseases Effects of Infectious Diseases
Diseases alter normal body function and/or Diseases alter normal body function and/or
structure.structure.
SymptomsSymptoms: Subjective feelings not obvious to an : Subjective feelings not obvious to an
observer. observer.
ExampleExample: Pain and malaise.: Pain and malaise.
SignsSigns: Objective changes that can be measured.: Objective changes that can be measured.
ExampleExample: Fever, redness, swelling, paralysis.: Fever, redness, swelling, paralysis.
SyndromeSyndrome: A group of signs and symptoms that : A group of signs and symptoms that
are associated with a disease.are associated with a disease.
ExampleExample: AIDS (Acquired Immune Deficiency : AIDS (Acquired Immune Deficiency
Syndrome) is a syndrome that varies from one Syndrome) is a syndrome that varies from one
individual to another.individual to another.
Diseases alter normal body function and/or Diseases alter normal body function and/or
structure.structure.
SymptomsSymptoms: Subjective feelings not obvious to an : Subjective feelings not obvious to an
observer. observer.
ExampleExample: Pain and malaise.: Pain and malaise.
SignsSigns: Objective changes that can be measured.: Objective changes that can be measured.
ExampleExample: Fever, redness, swelling, paralysis.: Fever, redness, swelling, paralysis.
SyndromeSyndrome: A group of signs and symptoms that : A group of signs and symptoms that
are associated with a disease.are associated with a disease.
ExampleExample: AIDS (Acquired Immune Deficiency : AIDS (Acquired Immune Deficiency
Syndrome) is a syndrome that varies from one Syndrome) is a syndrome that varies from one
individual to another.individual to another.
Classifying Infectious DiseasesClassifying Infectious Diseases
Communicable DiseasesCommunicable Diseases: Spread from one host to : Spread from one host to
another, directly or indirectly.another, directly or indirectly.
Example: Tuberculosis, herpes, flu, AIDS, Example: Tuberculosis, herpes, flu, AIDS,
chickenpox, mumps, polio, and hepatitis.chickenpox, mumps, polio, and hepatitis.
Contagious DiseasesContagious Diseases: Spread easily from one : Spread easily from one
person to another.person to another.
Example: Chickenpox and measles.Example: Chickenpox and measles.
Noncommunicable DiseasesNoncommunicable Diseases: Not spread from one : Not spread from one
host to another. Caused by microbes that live host to another. Caused by microbes that live
outside the body or by opportunistic pathogens that outside the body or by opportunistic pathogens that
live inside the body.live inside the body.
Example: Tetanus, botulism, and yeast infections. Example: Tetanus, botulism, and yeast infections.
Communicable DiseasesCommunicable Diseases: Spread from one host to : Spread from one host to
another, directly or indirectly.another, directly or indirectly.
Example: Tuberculosis, herpes, flu, AIDS, Example: Tuberculosis, herpes, flu, AIDS,
chickenpox, mumps, polio, and hepatitis.chickenpox, mumps, polio, and hepatitis.
Contagious DiseasesContagious Diseases: Spread easily from one : Spread easily from one
person to another.person to another.
Example: Chickenpox and measles.Example: Chickenpox and measles.
Noncommunicable DiseasesNoncommunicable Diseases: Not spread from one : Not spread from one
host to another. Caused by microbes that live host to another. Caused by microbes that live
outside the body or by opportunistic pathogens that outside the body or by opportunistic pathogens that
live inside the body.live inside the body.
Example: Tetanus, botulism, and yeast infections. Example: Tetanus, botulism, and yeast infections.
Disease OccurrenceDisease Occurrence
Disease IncidenceDisease Incidence: Percentage of population that : Percentage of population that
contractscontracts a disease in a given time period. a disease in a given time period.
Disease PrevalenceDisease Prevalence: Percentage of population : Percentage of population
that that hashas the disease during given time period. the disease during given time period.
Sporadic DiseaseSporadic Disease: Occurs only occasionally.: Occurs only occasionally.
Example: Polio in U.S.Example: Polio in U.S.
Endemic DiseaseEndemic Disease: Constantly present in the population.: Constantly present in the population.
Example: Common cold or ear infections.Example: Common cold or ear infections.
Epidemic DiseaseEpidemic Disease: Many people acquire disease in short : Many people acquire disease in short
time period.time period.
Example: Influenza, gonorrhea, chlamydia, and AIDS.Example: Influenza, gonorrhea, chlamydia, and AIDS.
Pandemic DiseasePandemic Disease: Worldwide epidemics.: Worldwide epidemics.
Example: Influenza and AIDS. Example: Influenza and AIDS.
Disease IncidenceDisease Incidence: Percentage of population that : Percentage of population that
contractscontracts a disease in a given time period. a disease in a given time period.
Disease PrevalenceDisease Prevalence: Percentage of population : Percentage of population
that that hashas the disease during given time period. the disease during given time period.
Sporadic DiseaseSporadic Disease: Occurs only occasionally.: Occurs only occasionally.
Example: Polio in U.S.Example: Polio in U.S.
Endemic DiseaseEndemic Disease: Constantly present in the population.: Constantly present in the population.
Example: Common cold or ear infections.Example: Common cold or ear infections.
Epidemic DiseaseEpidemic Disease: Many people acquire disease in short : Many people acquire disease in short
time period.time period.
Example: Influenza, gonorrhea, chlamydia, and AIDS.Example: Influenza, gonorrhea, chlamydia, and AIDS.
Pandemic DiseasePandemic Disease: Worldwide epidemics.: Worldwide epidemics.
Example: Influenza and AIDS. Example: Influenza and AIDS.
Reported AIDS Cases in the United States
Disease DurationDisease Duration
Acute DiseaseAcute Disease: Develops rapidly, but lasts a short : Develops rapidly, but lasts a short
time. time.
Examples: Flu and common cold.Examples: Flu and common cold.
Chronic DiseaseChronic Disease: Develops more slowly, and reactions : Develops more slowly, and reactions
are less severe. Tend to recur for long periods or to be are less severe. Tend to recur for long periods or to be
continual. continual.
Examples: Tuberculosis, hepatitis B, and infectious Examples: Tuberculosis, hepatitis B, and infectious
mononucleosis.mononucleosis.
Subacute DiseaseSubacute Disease: Intermediate between acute and : Intermediate between acute and
chronic.chronic.
Examples: Subacute bacterial endocarditis (streptococci). Examples: Subacute bacterial endocarditis (streptococci).
Latent DiseaseLatent Disease: Causative agent remains inactive for : Causative agent remains inactive for
a time, but then becomes active and produces disease a time, but then becomes active and produces disease
symptoms.symptoms.
Examples: Shingles, genital and oral herpes, AIDS.Examples: Shingles, genital and oral herpes, AIDS.
Acute DiseaseAcute Disease: Develops rapidly, but lasts a short : Develops rapidly, but lasts a short
time. time.
Examples: Flu and common cold.Examples: Flu and common cold.
Chronic DiseaseChronic Disease: Develops more slowly, and reactions : Develops more slowly, and reactions
are less severe. Tend to recur for long periods or to be are less severe. Tend to recur for long periods or to be
continual. continual.
Examples: Tuberculosis, hepatitis B, and infectious Examples: Tuberculosis, hepatitis B, and infectious
mononucleosis.mononucleosis.
Subacute DiseaseSubacute Disease: Intermediate between acute and : Intermediate between acute and
chronic.chronic.
Examples: Subacute bacterial endocarditis (streptococci). Examples: Subacute bacterial endocarditis (streptococci).
Latent DiseaseLatent Disease: Causative agent remains inactive for : Causative agent remains inactive for
a time, but then becomes active and produces disease a time, but then becomes active and produces disease
symptoms.symptoms.
Examples: Shingles, genital and oral herpes, AIDS.Examples: Shingles, genital and oral herpes, AIDS.
Host InvolvementHost Involvement
Local InfectionLocal Infection: Microbes are limited to small : Microbes are limited to small
area of body.area of body.
Examples: Boils, abscesses, and acne.Examples: Boils, abscesses, and acne.
Systemic (Generalized) InfectionSystemic (Generalized) Infection: Microbes are : Microbes are
spread throughout body by blood or lymph.spread throughout body by blood or lymph.
Examples: Measles, AIDS.Examples: Measles, AIDS.
BacteremiaBacteremia: Presence of bacteria in the blood.: Presence of bacteria in the blood.
SepticemiaSepticemia: Bacteria multiply in blood.: Bacteria multiply in blood.
ToxemiaToxemia: Presence of toxins in blood.: Presence of toxins in blood.
ViremiaViremia: Presence of viruses in blood.: Presence of viruses in blood.
Focal InfectionFocal Infection: Starts as a local infection and : Starts as a local infection and
spread to other parts of body.spread to other parts of body.
Examples: From teeth, tonsils, and appendix.Examples: From teeth, tonsils, and appendix.
Local InfectionLocal Infection: Microbes are limited to small : Microbes are limited to small
area of body.area of body.
Examples: Boils, abscesses, and acne.Examples: Boils, abscesses, and acne.
Systemic (Generalized) InfectionSystemic (Generalized) Infection: Microbes are : Microbes are
spread throughout body by blood or lymph.spread throughout body by blood or lymph.
Examples: Measles, AIDS.Examples: Measles, AIDS.
BacteremiaBacteremia: Presence of bacteria in the blood.: Presence of bacteria in the blood.
SepticemiaSepticemia: Bacteria multiply in blood.: Bacteria multiply in blood.
ToxemiaToxemia: Presence of toxins in blood.: Presence of toxins in blood.
ViremiaViremia: Presence of viruses in blood.: Presence of viruses in blood.
Focal InfectionFocal Infection: Starts as a local infection and : Starts as a local infection and
spread to other parts of body.spread to other parts of body.
Examples: From teeth, tonsils, and appendix.Examples: From teeth, tonsils, and appendix.
Host Resistance Determines Extent of InfectionHost Resistance Determines Extent of Infection
Primary InfectionPrimary Infection: Acute infection that causes : Acute infection that causes
initial illness.initial illness.
Example: Common coldExample: Common cold
Secondary InfectionSecondary Infection: Caused by opportunistic : Caused by opportunistic
pathogen after primary infection has weakened host pathogen after primary infection has weakened host
immune system.immune system.
Example: Pneumonia or bronchitis may develop Example: Pneumonia or bronchitis may develop
after the common cold.after the common cold.
Subclinical InfectionSubclinical Infection: Does not cause any noticeable : Does not cause any noticeable
illness in host.illness in host.
Example: Over 90% of polio infections are Example: Over 90% of polio infections are
asymptomatic.asymptomatic.
Primary InfectionPrimary Infection: Acute infection that causes : Acute infection that causes
initial illness.initial illness.
Example: Common coldExample: Common cold
Secondary InfectionSecondary Infection: Caused by opportunistic : Caused by opportunistic
pathogen after primary infection has weakened host pathogen after primary infection has weakened host
immune system.immune system.
Example: Pneumonia or bronchitis may develop Example: Pneumonia or bronchitis may develop
after the common cold.after the common cold.
Subclinical InfectionSubclinical Infection: Does not cause any noticeable : Does not cause any noticeable
illness in host.illness in host.
Example: Over 90% of polio infections are Example: Over 90% of polio infections are
asymptomatic.asymptomatic.
Spread of InfectionSpread of Infection
Reservoirs of InfectionReservoirs of Infection
Human ReservoirsHuman Reservoirs: Infected individuals who may : Infected individuals who may
or may not present disease. or may not present disease. CarriersCarriers are infected are infected
individuals without any signs or symptoms of individuals without any signs or symptoms of
disease (AIDS, polio, gonorrhea).disease (AIDS, polio, gonorrhea).
Animal ReservoirsAnimal Reservoirs: Zoonoses are diseases that : Zoonoses are diseases that
occur primarily in wild and domestic animals. occur primarily in wild and domestic animals.
About 150 different zoonoses are known (rabies, About 150 different zoonoses are known (rabies,
anthrax, and Lyme disease).anthrax, and Lyme disease).
Nonliving ReservoirsNonliving Reservoirs: Two major sources are soil : Two major sources are soil
and water.and water.
Soil: Soil: Clostridium tetaniClostridium tetani and and botulinumbotulinum..
Water: Water: Vibrio choleraeVibrio cholerae and and Salmonella typhiSalmonella typhi..
Reservoirs of InfectionReservoirs of Infection
Human ReservoirsHuman Reservoirs: Infected individuals who may : Infected individuals who may
or may not present disease. or may not present disease. CarriersCarriers are infected are infected
individuals without any signs or symptoms of individuals without any signs or symptoms of
disease (AIDS, polio, gonorrhea).disease (AIDS, polio, gonorrhea).
Animal ReservoirsAnimal Reservoirs: Zoonoses are diseases that : Zoonoses are diseases that
occur primarily in wild and domestic animals. occur primarily in wild and domestic animals.
About 150 different zoonoses are known (rabies, About 150 different zoonoses are known (rabies,
anthrax, and Lyme disease).anthrax, and Lyme disease).
Nonliving ReservoirsNonliving Reservoirs: Two major sources are soil : Two major sources are soil
and water.and water.
Soil: Soil: Clostridium tetaniClostridium tetani and and botulinumbotulinum..
Water: Water: Vibrio choleraeVibrio cholerae and and Salmonella typhiSalmonella typhi..
Transmission of DiseaseTransmission of Disease
I. Contact TransmissionI. Contact Transmission: Spread by direct contact, : Spread by direct contact,
indirect contact, or droplet transmission.indirect contact, or droplet transmission.
A. Direct Contact TransmissionA. Direct Contact Transmission: Person-to-person : Person-to-person
transmission. No intermediate object is involved. transmission. No intermediate object is involved.
Examples: Touching, kissing, sexual intercourse.Examples: Touching, kissing, sexual intercourse.
B. Indirect Contact TransmissionB. Indirect Contact Transmission: Agent is transferred : Agent is transferred
via a nonliving object (via a nonliving object (fomitefomite).).
Examples: Towels, eating utensils, thermometers, Examples: Towels, eating utensils, thermometers,
stethoscopes, bedding, clothes, money, and syringes. stethoscopes, bedding, clothes, money, and syringes.
C. Droplet TransmissionC. Droplet Transmission: Microbes are spread in mucus : Microbes are spread in mucus
droplets that travel droplets that travel short distancesshort distances ( (less than 1 meterless than 1 meter). ).
Examples: Sneezing, coughing, talking, and laughing.Examples: Sneezing, coughing, talking, and laughing.
I. Contact TransmissionI. Contact Transmission: Spread by direct contact, : Spread by direct contact,
indirect contact, or droplet transmission.indirect contact, or droplet transmission.
A. Direct Contact TransmissionA. Direct Contact Transmission: Person-to-person : Person-to-person
transmission. No intermediate object is involved. transmission. No intermediate object is involved.
Examples: Touching, kissing, sexual intercourse.Examples: Touching, kissing, sexual intercourse.
B. Indirect Contact TransmissionB. Indirect Contact Transmission: Agent is transferred : Agent is transferred
via a nonliving object (via a nonliving object (fomitefomite).).
Examples: Towels, eating utensils, thermometers, Examples: Towels, eating utensils, thermometers,
stethoscopes, bedding, clothes, money, and syringes. stethoscopes, bedding, clothes, money, and syringes.
C. Droplet TransmissionC. Droplet Transmission: Microbes are spread in mucus : Microbes are spread in mucus
droplets that travel droplets that travel short distancesshort distances ( (less than 1 meterless than 1 meter). ).
Examples: Sneezing, coughing, talking, and laughing.Examples: Sneezing, coughing, talking, and laughing.
Transmission of Microbial Disease
Direct Contact
Vehicle TransmissionVector Transmission
Droplet Transmission
Direct Contact
Vehicle TransmissionVector Transmission
Droplet Transmission
Transmission of Disease (Continued)Transmission of Disease (Continued)
II. Vehicle TransmissionII. Vehicle Transmission: Transmission of disease : Transmission of disease
via medium such as water, food, air, blood, body via medium such as water, food, air, blood, body
fluids, and intravenous fluids.fluids, and intravenous fluids.
Waterborne TransmissionWaterborne Transmission: Usually caused by water : Usually caused by water
contaminated with sewage.contaminated with sewage.
Airborne TransmissionAirborne Transmission: Spread of agents by droplets : Spread of agents by droplets
in dust that in dust that travel more than 1 mtravel more than 1 m to host. to host.
III. VectorsIII. Vectors: Animals that carry disease from one : Animals that carry disease from one
host to another. Arthropods (insects) are most host to another. Arthropods (insects) are most
important animal vectors.important animal vectors.
Mechanical TransmissionMechanical Transmission: Passive transport of : Passive transport of
pathogens on insect’s body.pathogens on insect’s body.
Biological TransmissionBiological Transmission: Pathogen spends part of its : Pathogen spends part of its
life cycle in the vector.life cycle in the vector.
II. Vehicle TransmissionII. Vehicle Transmission: Transmission of disease : Transmission of disease
via medium such as water, food, air, blood, body via medium such as water, food, air, blood, body
fluids, and intravenous fluids.fluids, and intravenous fluids.
Waterborne TransmissionWaterborne Transmission: Usually caused by water : Usually caused by water
contaminated with sewage.contaminated with sewage.
Airborne TransmissionAirborne Transmission: Spread of agents by droplets : Spread of agents by droplets
in dust that in dust that travel more than 1 mtravel more than 1 m to host. to host.
III. VectorsIII. Vectors: Animals that carry disease from one : Animals that carry disease from one
host to another. Arthropods (insects) are most host to another. Arthropods (insects) are most
important animal vectors.important animal vectors.
Mechanical TransmissionMechanical Transmission: Passive transport of : Passive transport of
pathogens on insect’s body.pathogens on insect’s body.
Biological TransmissionBiological Transmission: Pathogen spends part of its : Pathogen spends part of its
life cycle in the vector.life cycle in the vector.
Portals of Entry for MicrobesPortals of Entry for Microbes
SkinSkin: Most microbes cannot penetrate thick layers of : Most microbes cannot penetrate thick layers of
dead, dry cells. Some can enter through hair follicles dead, dry cells. Some can enter through hair follicles
and sweat glands. A few can penetrate unbroken skin and sweat glands. A few can penetrate unbroken skin
(hookworm and fungi)(hookworm and fungi)
Mucous MembranesMucous Membranes: Line respiratory, : Line respiratory,
gastrointestinal, urinary, eyes, and reproductive gastrointestinal, urinary, eyes, and reproductive
tracts. Thin, moist, and warm layer of living cells, tracts. Thin, moist, and warm layer of living cells,
Easier to penetrate (flu and cold viruses, many fungi, Easier to penetrate (flu and cold viruses, many fungi,
protozoa, and bacteria).protozoa, and bacteria).
Placenta: Placenta: Effective barrier to most pathogens. In 2% Effective barrier to most pathogens. In 2%
of pregnancies, pathogens cross placenta.of pregnancies, pathogens cross placenta.
Parenteral Route: Parenteral Route: Normal portal of entry is Normal portal of entry is
circumvented (punctures, bites, abrasions, surgical circumvented (punctures, bites, abrasions, surgical
wounds, etc).wounds, etc).
SkinSkin: Most microbes cannot penetrate thick layers of : Most microbes cannot penetrate thick layers of
dead, dry cells. Some can enter through hair follicles dead, dry cells. Some can enter through hair follicles
and sweat glands. A few can penetrate unbroken skin and sweat glands. A few can penetrate unbroken skin
(hookworm and fungi)(hookworm and fungi)
Mucous MembranesMucous Membranes: Line respiratory, : Line respiratory,
gastrointestinal, urinary, eyes, and reproductive gastrointestinal, urinary, eyes, and reproductive
tracts. Thin, moist, and warm layer of living cells, tracts. Thin, moist, and warm layer of living cells,
Easier to penetrate (flu and cold viruses, many fungi, Easier to penetrate (flu and cold viruses, many fungi,
protozoa, and bacteria).protozoa, and bacteria).
Placenta: Placenta: Effective barrier to most pathogens. In 2% Effective barrier to most pathogens. In 2%
of pregnancies, pathogens cross placenta.of pregnancies, pathogens cross placenta.
Parenteral Route: Parenteral Route: Normal portal of entry is Normal portal of entry is
circumvented (punctures, bites, abrasions, surgical circumvented (punctures, bites, abrasions, surgical
wounds, etc).wounds, etc).
Cross Section of Skin
Portals of ExitPortals of Exit
Site at which microbes leave body. Most common Site at which microbes leave body. Most common
exit portals are respiratory and gastrointestinal exit portals are respiratory and gastrointestinal
tracts.tracts.
Respiratory TractRespiratory Tract: Exit in discharges (mucus : Exit in discharges (mucus
droplets) from nose and mouth. Transmission by droplets) from nose and mouth. Transmission by
coughing, sneezing, spitting, etc.coughing, sneezing, spitting, etc.
Examples: Tuberculosis, influenza, pneumonia, Examples: Tuberculosis, influenza, pneumonia,
common cold, measles, mumps, scarlet fever, and common cold, measles, mumps, scarlet fever, and
meningococcal meningitis.meningococcal meningitis.
Gastrointestinal TractGastrointestinal Tract: Exit in feces or saliva.: Exit in feces or saliva.
Feces: Amoebas, poliovirus, cholera, typhoid fever, Feces: Amoebas, poliovirus, cholera, typhoid fever,
salmonella, shigella, and many helminths.salmonella, shigella, and many helminths.
Saliva: Rabies virus, herpes simplex 1.Saliva: Rabies virus, herpes simplex 1.
Site at which microbes leave body. Most common Site at which microbes leave body. Most common
exit portals are respiratory and gastrointestinal exit portals are respiratory and gastrointestinal
tracts.tracts.
Respiratory TractRespiratory Tract: Exit in discharges (mucus : Exit in discharges (mucus
droplets) from nose and mouth. Transmission by droplets) from nose and mouth. Transmission by
coughing, sneezing, spitting, etc.coughing, sneezing, spitting, etc.
Examples: Tuberculosis, influenza, pneumonia, Examples: Tuberculosis, influenza, pneumonia,
common cold, measles, mumps, scarlet fever, and common cold, measles, mumps, scarlet fever, and
meningococcal meningitis.meningococcal meningitis.
Gastrointestinal TractGastrointestinal Tract: Exit in feces or saliva.: Exit in feces or saliva.
Feces: Amoebas, poliovirus, cholera, typhoid fever, Feces: Amoebas, poliovirus, cholera, typhoid fever,
salmonella, shigella, and many helminths.salmonella, shigella, and many helminths.
Saliva: Rabies virus, herpes simplex 1.Saliva: Rabies virus, herpes simplex 1.
Portals of Exit (Continued)Portals of Exit (Continued)
Urogenital TractUrogenital Tract: Exit in secretions or urine.: Exit in secretions or urine.
Penis and vagina: Sexually transmitted diseases. Penis and vagina: Sexually transmitted diseases.
Chlamydia, herpes simplex 2, HIV, gonorrhea, and Chlamydia, herpes simplex 2, HIV, gonorrhea, and
syphilis.syphilis.
Urine: Brucellosis and typhoid fever.Urine: Brucellosis and typhoid fever.
Skin and Wound InfectionsSkin and Wound Infections: Spread through : Spread through
direct contact or through fomites.direct contact or through fomites.
Example: Example: S. aureus, P. aeruginosaS. aureus, P. aeruginosa, scabies, , scabies,
ringworm.ringworm.
BloodBlood: Transmission through insects, needles, : Transmission through insects, needles,
and syringes.and syringes.
Insects: Malaria, yellow fever, and Lyme disease.Insects: Malaria, yellow fever, and Lyme disease.
Needles: AIDS and hepatitis B.Needles: AIDS and hepatitis B.
Urogenital TractUrogenital Tract: Exit in secretions or urine.: Exit in secretions or urine.
Penis and vagina: Sexually transmitted diseases. Penis and vagina: Sexually transmitted diseases.
Chlamydia, herpes simplex 2, HIV, gonorrhea, and Chlamydia, herpes simplex 2, HIV, gonorrhea, and
syphilis.syphilis.
Urine: Brucellosis and typhoid fever.Urine: Brucellosis and typhoid fever.
Skin and Wound InfectionsSkin and Wound Infections: Spread through : Spread through
direct contact or through fomites.direct contact or through fomites.
Example: Example: S. aureus, P. aeruginosaS. aureus, P. aeruginosa, scabies, , scabies,
ringworm.ringworm.
BloodBlood: Transmission through insects, needles, : Transmission through insects, needles,
and syringes.and syringes.
Insects: Malaria, yellow fever, and Lyme disease.Insects: Malaria, yellow fever, and Lyme disease.
Needles: AIDS and hepatitis B.Needles: AIDS and hepatitis B.
Nosocomial (Hospital Acquired) InfectionsNosocomial (Hospital Acquired) Infections
““Nosocomial”Nosocomial” Greek word for hospital. Greek word for hospital.
Infections acquired at a health care facility.Infections acquired at a health care facility.
According to According to Center for Disease ControlCenter for Disease Control (CDC), (CDC), 5-5-
15%15% of all hospital patients acquire N.I.s. of all hospital patients acquire N.I.s.
At least At least 100,000 deaths100,000 deaths in US from N.I.s every year. in US from N.I.s every year.
About About 1.7 million1.7 million nosocomial infections per year in US. nosocomial infections per year in US.
Predisposing Factors:Predisposing Factors:
Wide variety of microbes in hospital environmentWide variety of microbes in hospital environment
Weakened or immunocompromised patientsWeakened or immunocompromised patients
Chain of transmission: Mainly through direct or indirect Chain of transmission: Mainly through direct or indirect
contact.contact.
•From health care workers to patientFrom health care workers to patient
•From patient to patientFrom patient to patient
•Fomites: Catheters, needles, dressings, beds, wheelchairsFomites: Catheters, needles, dressings, beds, wheelchairs
•Airborne transmissionAirborne transmission
““Nosocomial”Nosocomial” Greek word for hospital. Greek word for hospital.
Infections acquired at a health care facility.Infections acquired at a health care facility.
According to According to Center for Disease ControlCenter for Disease Control (CDC), (CDC), 5-5-
15%15% of all hospital patients acquire N.I.s. of all hospital patients acquire N.I.s.
At least At least 100,000 deaths100,000 deaths in US from N.I.s every year. in US from N.I.s every year.
About About 1.7 million1.7 million nosocomial infections per year in US. nosocomial infections per year in US.
Predisposing Factors:Predisposing Factors:
Wide variety of microbes in hospital environmentWide variety of microbes in hospital environment
Weakened or immunocompromised patientsWeakened or immunocompromised patients
Chain of transmission: Mainly through direct or indirect Chain of transmission: Mainly through direct or indirect
contact.contact.
•From health care workers to patientFrom health care workers to patient
•From patient to patientFrom patient to patient
•Fomites: Catheters, needles, dressings, beds, wheelchairsFomites: Catheters, needles, dressings, beds, wheelchairs
•Airborne transmissionAirborne transmission
Factors Contributing to Nosocomial Infections
Important Nosocomial PathogensImportant Nosocomial Pathogens
Normal microbiota:Normal microbiota: Many are opportunistic Many are opportunistic
pathogenspathogens
Antibiotic resistanceAntibiotic resistance: Very high due to the use of : Very high due to the use of
antimicrobials in health care facilities.antimicrobials in health care facilities.
Principle microorganismsPrinciple microorganisms: Used to be gram-: Used to be gram-
positive microbes. Today positive microbes. Today mostmost are are gram-negative gram-negative
bacteria.bacteria.
EnterobacteriaEnterobacteria: Over 40% of all infections. : Over 40% of all infections. E. coli, E. coli,
Klebsiella spp., Proteus spp., Enterobacter sppKlebsiella spp., Proteus spp., Enterobacter spp., and ., and
Serratia marcescensSerratia marcescens..
Staphylococcus aureusStaphylococcus aureus (11%)(11%)
FungiFungi: (10%) : (10%) C. albicansC. albicans and others and others
EnterococcusEnterococcus (10%)(10%)
Pseudomonas aeruginosaPseudomonas aeruginosa (9%) (9%)
Normal microbiota:Normal microbiota: Many are opportunistic Many are opportunistic
pathogenspathogens
Antibiotic resistanceAntibiotic resistance: Very high due to the use of : Very high due to the use of
antimicrobials in health care facilities.antimicrobials in health care facilities.
Principle microorganismsPrinciple microorganisms: Used to be gram-: Used to be gram-
positive microbes. Today positive microbes. Today mostmost are are gram-negative gram-negative
bacteria.bacteria.
EnterobacteriaEnterobacteria: Over 40% of all infections. : Over 40% of all infections. E. coli, E. coli,
Klebsiella spp., Proteus spp., Enterobacter sppKlebsiella spp., Proteus spp., Enterobacter spp., and ., and
Serratia marcescensSerratia marcescens..
Staphylococcus aureusStaphylococcus aureus (11%)(11%)
FungiFungi: (10%) : (10%) C. albicansC. albicans and others and others
EnterococcusEnterococcus (10%)(10%)
Pseudomonas aeruginosaPseudomonas aeruginosa (9%) (9%)
Principal Kinds of Nosocomial InfectionsPrincipal Kinds of Nosocomial Infections
34
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20
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Urinary TractSurgical SiteLower
Respiratory
BacteremiaOther, skin,
central line
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34
17
13
14
22
0
5
10
15
20
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Urinary TractSurgical SiteLower
Respiratory
BacteremiaOther, skin,
central line
P
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Control of Nosocomial InfectionsControl of Nosocomial Infections
Aseptic techniques to avoid contaminationAseptic techniques to avoid contamination
Careful handling and disposal of contaminated Careful handling and disposal of contaminated
materialmaterial
Frequent and adequate hand washingFrequent and adequate hand washing
Proper infection control training of staffProper infection control training of staff
Isolation wards and roomsIsolation wards and rooms
Avoid unnecessary antibiotic prescriptionsAvoid unnecessary antibiotic prescriptions
Avoid unnecessary invasive proceduresAvoid unnecessary invasive procedures
Regular disinfection of respirators and Regular disinfection of respirators and
humidifiers and maintenance of autoclaveshumidifiers and maintenance of autoclaves
Use disposable and/or sterile suppliesUse disposable and/or sterile supplies
Infection control committeeInfection control committee
Aseptic techniques to avoid contaminationAseptic techniques to avoid contamination
Careful handling and disposal of contaminated Careful handling and disposal of contaminated
materialmaterial
Frequent and adequate hand washingFrequent and adequate hand washing
Proper infection control training of staffProper infection control training of staff
Isolation wards and roomsIsolation wards and rooms
Avoid unnecessary antibiotic prescriptionsAvoid unnecessary antibiotic prescriptions
Avoid unnecessary invasive proceduresAvoid unnecessary invasive procedures
Regular disinfection of respirators and Regular disinfection of respirators and
humidifiers and maintenance of autoclaveshumidifiers and maintenance of autoclaves
Use disposable and/or sterile suppliesUse disposable and/or sterile supplies
Infection control committeeInfection control committee
Control of Nosocomial Infections
Predisposing Factors for DiseasePredisposing Factors for Disease
Factors that make an individual more susceptible Factors that make an individual more susceptible
to a given disease.to a given disease.
GenderGender
Genetic factorsGenetic factors
Climate and weatherClimate and weather
NutritionNutrition
Fatigue/StressFatigue/Stress
OccupationOccupation
EnvironmentEnvironment
LifestyleLifestyle
AgeAge
Other illnessOther illness
Factors that make an individual more susceptible Factors that make an individual more susceptible
to a given disease.to a given disease.
GenderGender
Genetic factorsGenetic factors
Climate and weatherClimate and weather
NutritionNutrition
Fatigue/StressFatigue/Stress
OccupationOccupation
EnvironmentEnvironment
LifestyleLifestyle
AgeAge
Other illnessOther illness
Development of an Infectious DiseaseDevelopment of an Infectious Disease
1. Incubation Period1. Incubation Period: Time between initial : Time between initial
infection and appearance of signs and symptomsinfection and appearance of signs and symptoms
2. Prodromal Period2. Prodromal Period: Early, mild symptoms of : Early, mild symptoms of
disease.disease.
3. Illness Period3. Illness Period: Disease is most acute. Overt : Disease is most acute. Overt
signs and symptoms. Patient immune system signs and symptoms. Patient immune system
actively fights off infection. If not successful may actively fights off infection. If not successful may
die at this stage.die at this stage.
4. Decline Period4. Decline Period: Signs and symptoms subside. : Signs and symptoms subside.
Patient is vulnerable to secondary infections.Patient is vulnerable to secondary infections.
5. Convalescence Period5. Convalescence Period: Recovery. Body returns : Recovery. Body returns
to predisease state.to predisease state.
1. Incubation Period1. Incubation Period: Time between initial : Time between initial
infection and appearance of signs and symptomsinfection and appearance of signs and symptoms
2. Prodromal Period2. Prodromal Period: Early, mild symptoms of : Early, mild symptoms of
disease.disease.
3. Illness Period3. Illness Period: Disease is most acute. Overt : Disease is most acute. Overt
signs and symptoms. Patient immune system signs and symptoms. Patient immune system
actively fights off infection. If not successful may actively fights off infection. If not successful may
die at this stage.die at this stage.
4. Decline Period4. Decline Period: Signs and symptoms subside. : Signs and symptoms subside.
Patient is vulnerable to secondary infections.Patient is vulnerable to secondary infections.
5. Convalescence Period5. Convalescence Period: Recovery. Body returns : Recovery. Body returns
to predisease state.to predisease state.
The Stages of an Infectious Disease
EpidemiologyEpidemiology
Science that studies when and where diseases Science that studies when and where diseases
occur and how they are transmitted in a occur and how they are transmitted in a
population.population.
Modern epidemiology began in 1848 during a Modern epidemiology began in 1848 during a
cholera epidemic in London.cholera epidemic in London.
Epidemiologists collect information to determine:Epidemiologists collect information to determine:
EtiologyEtiology: Cause of disease (pathogen).: Cause of disease (pathogen).
Predisposing factorsPredisposing factors: Age, sex, lifestyle, etc.: Age, sex, lifestyle, etc.
IncidenceIncidence: Number of individuals acquiring disease in : Number of individuals acquiring disease in
a given time period.a given time period.
PrevalencePrevalence: Number of individuals with disease in a : Number of individuals with disease in a
given time period.given time period.
TransmissionTransmission
Public Health Policy and PreventionPublic Health Policy and Prevention
Science that studies when and where diseases Science that studies when and where diseases
occur and how they are transmitted in a occur and how they are transmitted in a
population.population.
Modern epidemiology began in 1848 during a Modern epidemiology began in 1848 during a
cholera epidemic in London.cholera epidemic in London.
Epidemiologists collect information to determine:Epidemiologists collect information to determine:
EtiologyEtiology: Cause of disease (pathogen).: Cause of disease (pathogen).
Predisposing factorsPredisposing factors: Age, sex, lifestyle, etc.: Age, sex, lifestyle, etc.
IncidenceIncidence: Number of individuals acquiring disease in : Number of individuals acquiring disease in
a given time period.a given time period.
PrevalencePrevalence: Number of individuals with disease in a : Number of individuals with disease in a
given time period.given time period.
TransmissionTransmission
Public Health Policy and PreventionPublic Health Policy and Prevention
Epidemiological Data
Types of Epidemiological InvestigationTypes of Epidemiological Investigation
Descriptive EpidemiologyDescriptive Epidemiology: Retrospective studies : Retrospective studies
that collect data on diseases occurence.that collect data on diseases occurence.
Examples: Initial studies on toxic shock syndrome Examples: Initial studies on toxic shock syndrome
outbreaks.outbreaks.
Analytical EpidemiologyAnalytical Epidemiology: Analyzes a disease to : Analyzes a disease to
determine its probable cause.determine its probable cause.
Case control methodCase control method: Look for factors that precede : Look for factors that precede
disease. Compare sick individuals to healthy disease. Compare sick individuals to healthy
individuals.individuals.
Cohort methodCohort method: Study two populations, one that has : Study two populations, one that has
been exposed to a certain risk factor (e.g.: blood been exposed to a certain risk factor (e.g.: blood
transfusion or sexual contact) . Control group is not transfusion or sexual contact) . Control group is not
exposed to risk factor.exposed to risk factor.
Experimental EpidemiologyExperimental Epidemiology: Test drugs or : Test drugs or
vaccines on susceptible populations.vaccines on susceptible populations.
Descriptive EpidemiologyDescriptive Epidemiology: Retrospective studies : Retrospective studies
that collect data on diseases occurence.that collect data on diseases occurence.
Examples: Initial studies on toxic shock syndrome Examples: Initial studies on toxic shock syndrome
outbreaks.outbreaks.
Analytical EpidemiologyAnalytical Epidemiology: Analyzes a disease to : Analyzes a disease to
determine its probable cause.determine its probable cause.
Case control methodCase control method: Look for factors that precede : Look for factors that precede
disease. Compare sick individuals to healthy disease. Compare sick individuals to healthy
individuals.individuals.
Cohort methodCohort method: Study two populations, one that has : Study two populations, one that has
been exposed to a certain risk factor (e.g.: blood been exposed to a certain risk factor (e.g.: blood
transfusion or sexual contact) . Control group is not transfusion or sexual contact) . Control group is not
exposed to risk factor.exposed to risk factor.
Experimental EpidemiologyExperimental Epidemiology: Test drugs or : Test drugs or
vaccines on susceptible populations.vaccines on susceptible populations.
Case ReportingCase Reporting
Procedure that requires health workers to report Procedure that requires health workers to report
specifiedspecified diseases to government agencies. diseases to government agencies.
Partial listPartial list of 63 reportable diseases in the U.S. (2005): of 63 reportable diseases in the U.S. (2005):
AIDSAIDSAnthraxAnthrax
BotulismBotulism BrucellosisBrucellosis
Chlamydia (genital)Chlamydia (genital)CholeraCholera
DiphtheriaDiphtheriaEnterohemorrhagic Enterohemorrhagic E. coliE. coli
GonorrheaGonorrheaHansen’s Disease (Leprosy)Hansen’s Disease (Leprosy)
Hepatitis A, B, and CHepatitis A, B, and CHIV infectionHIV infection
Lyme DiseaseLyme DiseaseMalariaMalaria
MeaslesMeasles MumpsMumps
PlaguePlagueRabiesRabies
RubellaRubella SyphilisSyphilis
TetanusTetanus TuberculosisTuberculosis
Varicella (deaths only)Varicella (deaths only)Yellow feverYellow fever
Procedure that requires health workers to report Procedure that requires health workers to report
specifiedspecified diseases to government agencies. diseases to government agencies.
Partial listPartial list of 63 reportable diseases in the U.S. (2005): of 63 reportable diseases in the U.S. (2005):
AIDSAIDSAnthraxAnthrax
BotulismBotulism BrucellosisBrucellosis
Chlamydia (genital)Chlamydia (genital)CholeraCholera
DiphtheriaDiphtheriaEnterohemorrhagic Enterohemorrhagic E. coliE. coli
GonorrheaGonorrheaHansen’s Disease (Leprosy)Hansen’s Disease (Leprosy)
Hepatitis A, B, and CHepatitis A, B, and CHIV infectionHIV infection
Lyme DiseaseLyme DiseaseMalariaMalaria
MeaslesMeasles MumpsMumps
PlaguePlagueRabiesRabies
RubellaRubella SyphilisSyphilis
TetanusTetanus TuberculosisTuberculosis
Varicella (deaths only)Varicella (deaths only)Yellow feverYellow fever
Case ReportingCase Reporting
Center for Disease Prevention and Control Center for Disease Prevention and Control
(CDC)(CDC)
Central source of epidemiological information in Central source of epidemiological information in
U.S.U.S.
Branch of U.S. Public Health ServiceBranch of U.S. Public Health Service
Located in Atlanta, GeorgiaLocated in Atlanta, Georgia
Weekly publication “Morbidity and Mortality Weekly publication “Morbidity and Mortality
Report” (MMWR)Report” (MMWR)
MorbidityMorbidity: Number of specific notifiable diseases.: Number of specific notifiable diseases.
MortalityMortality: Number of deaths from diseases.: Number of deaths from diseases.
Reports on disease outbreaksReports on disease outbreaks
Special interest case historiesSpecial interest case histories
Summaries on status of diseasesSummaries on status of diseases
Recommendations for diagnosis, immunization, and Recommendations for diagnosis, immunization, and
treatment.treatment.
(CDC)(CDC)
Central source of epidemiological information in Central source of epidemiological information in
U.S.U.S.
Branch of U.S. Public Health ServiceBranch of U.S. Public Health Service
Located in Atlanta, GeorgiaLocated in Atlanta, Georgia
Weekly publication “Morbidity and Mortality Weekly publication “Morbidity and Mortality
Report” (MMWR)Report” (MMWR)
MorbidityMorbidity: Number of specific notifiable diseases.: Number of specific notifiable diseases.
MortalityMortality: Number of deaths from diseases.: Number of deaths from diseases.
Reports on disease outbreaksReports on disease outbreaks
Special interest case historiesSpecial interest case histories
Summaries on status of diseasesSummaries on status of diseases
Recommendations for diagnosis, immunization, and Recommendations for diagnosis, immunization, and
treatment.treatment.
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