Investigation of Acute Gastroenteritis Epidemic (AGE) and its steps

Steps of investigation of any epidemic are illustrated in the given slide especially for acute gastro-enteritis epidemic. Also the prevention of AGE is also given and at the end how to submit a report is also given.

1. Steps of Investigation of an Epidemic of Acute G astroenteritis (AGE) Mohsin Ahmed Ansari II MBBS

2. Investigation of an epidemic Epidemic is defined as a localised occurrence of increased incidence of a particular disease. occurrence of an epidemic always signals some significant shift in the existing balance between the agent, host and environment Becomes a public health emergency whenever it affects a large number of people within community and there’s a need of thorough investigation an implementation of control measures. Epidemiology has an important role to play in the investigation of epidemics

3. Objectives of Epidemic Investigation To know the distribution of the outbreak in the community with refernce to time, place and person including environmental condition. To know the magnitude of the problem in terms of morbidity and mortality To identify the causative agent, source of infection, mode of transmission. To implement immediate control measures To give recommendations for preventions of future recurrences of the same epidemic.

4. Gastroenteritis and its prevention Gastroenteritis is a prescribed contagious condition under the public health Act (2005) ,so if a suspected outbreak of gastroenteritis take place, it is vital that steps are taken to protect the health of the camper’s and the wide community . The most important ways to prevent a viral gastroenteritis outbreak in a camp facility are routine through hand washing and rapid isolation or exclusion of people when they became ill, Prevention include :- Good hygiene: An important way to minimize the spread of gastroenteritis is to ensure to keep unwashed hands away from mouth. Food supply: The prevention of foodborne illness involves attention to hygiene, Proper handling and preparation of food and care during food storage and distribution. Water supply: Water for consumption or food preparation should be free from viruses , bacteria, parasites and chemicals that can cause diseases. Screening and monitoring campers and staff upon arrival to the camp and throughout their stay:- Before departing for camp , ask whether any campers/staff had vomiting or diarrhoea in the last 48 hours. If anyone has, they should not attend the camp until they have been free of symptoms for 48 hrs. Exclusion/isolation/removal of sick camper’s and staff:- People with vomiting and diarrhoea should be excluded from or isolated within the camp until at least 48 hrs. after the symptoms have stopped e.g. they have not had a loose bowel action or vomited for at least 48 hrs. Rapid access to more staff and medical assistance in the event of an outbreak - The camp facility is to have the contact phone number’s handy for ambulance, local hospital ,local doctor and the nearest police health unit.

5. Gastroenteritis and its prevention ( contd ) To manage and contain the gastroenteritis outbreak in a camp facility includes:- Isolation of sick people:- To minimize the spread of this illness, people with symptoms of gastroenteritis should be separated from the rest of the group Seeking medical attention:- If any sick person or groups of people requires medical treatment , telephone ahead and inform the ambulance , hospital or general practitioner that you are coming with one or more cases of gastroenteritis. Early identification of all sick people:- The early identification and management of a person or group of people experiencing nausea , vomiting and/or diarrhoea is essential if a large outbreak is to be avoided. Collection of laboratory samples:- Arranging collection of samples will increase the likelihood that the cause of the outbreak can be identified. Notifying the local public health unit Good hygiene:- check ,reinforce and ramp up good hygiene practices. Cleaning of facility (both during and after an outbreak):- Some organisms can remain viable on surface for a prolonged period of time and are therefore able to infect others during and even after the outbreak appear to be over . To prevent transmission via contaminated surfaces particularly attention to environmental cleaning is needed. Transportation to medical care/or home:- To a health care facility; from a health care facility back to camp; from a health care facility to their home. Advice to staff , campers and visitors/volunteers on management of sick people and prevention of further cases.

6. Steps involved in the investigation

7. 1. Confirmation of epidemic For confirmation of outbreak has happened , usual or normal level of the condition being investigated must be known . Done by comparing no. of cases occurring in current period and the no. of cases in comparable period in the past . Occurrence of cares of similar illness attending a dispensary or hospital should arouse suspicion of an outbreak. Case eg: Few cases of Jaundice in a hospital of south Dum Dum , Kolkata , in april 2004 resulting in investigation leading to outbreak of viral hepatitis E . 6 cases of gastro- enteritis were present in500 hospitalized children in April 1780 and the toll rises to 364 cases of gastro-enteritis amongst 762 cases in May, 1980. In village Kanzat of Gujarat with about 3900 population an outbreak of acute watery diarrhoea with vomiting Started on 30th sept 2002.300 cases occurred giving an attack rate of 8 %. The occurrence of single case of an eliminated disease (like guinea worm or plague)or an uncommon disease like hemorrhagic fever should start investigation . A single case of vaccine preventable disease under surveillance should ring a bell . An outbreak of very rare diseases like human anthrax poses special challenge.

8. 1. Confirmation of epidemic (contd.) Drastic increase in Cases occurring in hospitals are easily noticed but information on the occurrence of community is not easily available . Information maybe collected from routine health service records eg. OPD registers, in-patient registers etc . Information should also be collected not only from modern medicine practitioners but also from other systems like dispensaries, E.S.I.S . dispensaries, local healer etc. In an investigation of Viral hepatitis in Aurangabad, information became available from local healer treating jaundice. Excess mortality technique is also used to find out increased incidence of not only mortality but condition like absentees in school or occupation, morbidity, OPD attendance, fever cares etc . Increase in population may also be responsible for giving rise to a higher absolute number of cases Increase in occurrence may also be due to seasonal fluctuation. comparison is valid between similar season onIy . Certain diseases are masked seasonal variation and care must be taken in declaring an epidemic when season has changed . Rapid Fluctuation in immunity also give rise to fluctuation. Eg. by migration of susceptible may also give rise to fluctuations. Occasionally exaggerated reports of occurrence of a condition and multiple reporting cause an impression of epidemic. Rumors spread fast especially of emotional Involvement . eg. death of children due to encephalitis, meningitis and the no. of death reported in rumor kept on increasing. Epidemic diseases also slows peaks & troughs in their occurrence and the possibility of a peak endemic level must be considered before coming to the conclusion of epidemic incidence .

9. 2. Confirmation of diagnosis The report may be spurious due to misinterpretation of signs. Or symptoms by public or health worker. It is not necessary to examine all the cases. C linical examination of a sample of cases is sufficient Lab investigations where applicable are most useful to confirm the diagnosis but control measures should not be delayed until laboratory results are available. Verification is important as control measures are disease specific A qualified physician reviews clinical and lab findings to correlate diagnosis and patient history. Summarizing clinical features with frequency distribution after diagnosing the cases to characterise spectrum of illness.

10. 3 . Collection of relevant ecological info Some imbalance in the equilibrium between agent , host and environment is responsible for the occurrence of an epidemic. The disease may be an endemic one increasing to epidemic proportion or may be a non-endemic one and introduced from outside . Depending upon the suspected identify and mode of transmission, information should be collected to find out the circumstances which have favored transmission . Epidemic of respiratory disease may have been caused by sudden thermal change like cold wave, occurrence of air pollution, spell of cold season keeping people indoors with closed windows , etc. Vector-borne diseases may increase if the climatic conditions favor the arthropods survival or increased density. Migration of people may have upset the epidemiological balance .In case of gastrointestinal infections, search should be made to find out how the transmission of pathogen could have occurred from the case or carrier to the susceptible . In case water-borne transmission is suspected ,a sanitary survey of the water supply system from source to the consumer should be carried out systematically . Characteristics of the persons affected or spared and geographical distribution also provide information ,which helps to find any unusual happening favoring increased incidence. Such events may be natural occurrence like unseasonal or heavy rainfall .Such events were responsible for causing fecal pollution of a city water supply leading to the world's largest epidemic of typhoid fever. Seasonal changes in the course of a river may lead to foecal contamination of water supply and occurence of an epidemic .

11. 4. Distribution of epidemic Time distribution: By plotting the number of cases against the dates on a graph, the curve so obtained is called ‘ Epidemic curve ’ and the shape of the curve helps to know the type of the epidemic. Place distribution: By plotting the number of cases as ‘Dots’ or ‘Stars’ with respect to their localities in the geographical area map . This is called ‘Geographical spot/shaded map ’. The pictorial presentation shows at a glance , the area of high and low density. The area of high density gives a clue about the source of infection and even the mode of spread.

12. 4. Distribution of epidemic (contd.) Person distribution of the epidemic: This is studied by collecting the following data – Total population of the area Total number of persons being affected Total number of deaths, if any Age wise and sex wise distribution of the diseased and the dead. The “population at risk” can thus be defined, which becomes the denominator to calculate the Attack rate. The other relevant characteristics such as their movement to any pilgrimage center , etc. is also noted down. All these information is recorded in epidemiological case sheet.

13. 5. Rapid search for all the cases The search for new cases (secondary cases) should be carried out everyday, till the area is declared free of epidemic. This period is usually taken as twice the incubation period of the disease since the occurrence of last case . Rapid search is made by the area health worker by door to door survey to detect many more such new cases . The patient may be asked if he knew of other cases in the home, family, neighbourhood , school, work place having an onset within the incubation of the index case . Cases admitted to the local hospitals should also be taken into consideration. This may reveal not only additional cases but also person-to-person spread .

14. 6 . Data analysis The data collected should be analyzed on ongoing basis, using the classical epidemiological parameters - time, place and person. If the disease agent is known, the characteristics of time, place and person may be rearranged into Agent- Host-Environment model. The data is now analyzed to know the magnitude of the problem by calculating morbidity (attack ) rate and mortality (case fatality) rates. Incidence rate and prevalence rate are not studied because it is an epidemic .

15. 7 . Formulation etiological hypothesis A hypothesis is a proposition or a tentative theory designed to explain the observed distribution of the disease . Based upon the information collected, it is usually possible to formulate one or more hypothesis for explaining the epidemic behavior of the disease and also the circumstances leading to the epidemic . Finding out associations between variables facilitates this The stronger the statistical association, the more useful it is for supporting a hypothesis. The value of a hypothesis is inversely related to the no. of alternative plausible hypothesis. The occurrence of an isolated or unusual case may give clue or provide support to a hypothesis . Formulation is done in terms of the diagnosis, causative agent, possible source of infection, mode of spread, environmental factors favoring the occurrence of the epidemic. For eg: it is an outbreak of acute gastroenteritis, caused by Vibrio el tor organisms, transmitted from the river/well , through water.

16. 8. Testing of hypothesis Testing of hypotheses may or may not be necessary but further evidence can be collected to give additional support if needed to substantiate one final hypotheses . Typically, hypotheses in a field investigation are evaluated using a combination of environmental evidence, laboratory science and epidemiology. From an epidemiological point of view, hypotheses are evaluated in one of the two ways- either by comparing the hypotheses with the established facts or by using an analytic epidemiology. Two most commonly used analytical studies in outbreaks are cohort study and case control study. These study can determine how likely it is that a certain factor is the cause of the outbreak . In addition to analytical epidemiological studies, an environmental investigation can also help confirm the hypotheses. Example- In a food borne outbreak, the environmental investigation could identify factors like contaminated eggs, improper food storage or poor hygiene standard that may have contributed to or cause the outbreak. Hypotheses should be- Plausible Biologically acceptable Explainatory in causative agent , source, mode of transmission, time of exposition.

17. 8. Testing of hypothesis ( contd ) The hypothesis can be tested by doing ‘case-control’ study to calculate exposure rate. If exposure rate is more among cases than among controls, then there is an association between the suspected factor and the disease .

18. 9. Action plan based on applied hypothesis This activity is not a part of the process of epidemiological investigation, yet one of essential inseparable reasons for carrying out the investigation. The treatment and relief to the affected persons and steps to control the epidemic is essential. In the event of acute gastroenteritis outbreak in a camp facility, following actions are supposed to be taken to support the affected people:- Immediate isolate people experiencing nausea , vomiting and/or diarrhoea . Seek medical attention without any delay . Arrange transport for ill people , while continuing to isolate people with symptoms from the remainder of the group . Maintain a plentiful supply of drinking water and fluids to the sick and seek medical advice if symptoms do not settle or if concerned . Consider oral replacement therapy fluids in severe or prolonged cases . Collection of laboratory samples . Notify to local public health unit

19. 10. Further collection of data Further collection of data is necessary to validate the hypothesis which enables - Detection of common risk Identification of associations between different variables Looking for concomitant variation in incidence following the preventive measure taken Finding out the reasons for inconsistencies between observation made and events expected on the basis of hypothesis formulated This can be done by : Survey of a representative samples of total population under study-this is generally sufficient and gives accurate data . Laboratory test ( special) required to obtain further information-as provisional diagnosis is only based on clinical evidence and for a definitive diagnosis-to study infection with atypical, mild or sub-clinical attacks-prior information to the laboratory are required for obtaining laboratory support Other lab investigation to obtain additional supporting information:-water sample may be examined chemically and bacteriologically to obtain evidence of fecal contamination.

20. 11. Evaluation of ecological factors Ecological factors which have made the epidemic possible should be investigated to prevent further transmission of the disease, such as sanitary status of eating establishments, water and milk supply; breakdown in the water supply system; movements of the human population, atmospheric changes such as temperature, humidity and air pollution, population dynamics of insects and animal reservoirs . Contamination of water occur at a point of time only or intermittently and there may be no pathogen at the time of sample collection. Dilution takes place to a large degree when contaminated with feces and sewage in a large body of water Presence of coliform indicator organism or chemical evidence of fecal contamination may provide support eg: Cases of infectious hepatitis taking place in houses in Pune-food sample(except in chemical contamination ) e g: Suspected viral fever in Aurangabad city.

21. 12. Submission of report - report of investigation The report of epidemiological investigation should be written in a systemic way . The report should be complete, concise and relevant with necessary information. Final report should include the following information: It should give introduction and necessary background information. Background information includes — Geographical location Climatic conditions . Demographic status(population pyramid ) Socio-economic situation . Organization of health services . Surveillance if early warning symptoms . Normal disease prevalence . H istorical data – Previous occurrence of epidemics - Of the same disease; Locally or elsewhere . Occurrence of related disease if any - in the same area; in other areas; discovery of the first cases of the present outbreak. Methodology of investigation which includes – Case definition Questionnaire used in epidemiological investigation. Survey terms- Household survey; Retrospective survey; Prospective surveillance-Collection of laboratory specimens; Laboratory techniques

22. 12. Submission of report ( contd ) d . ANALYSIS OF DATA – Clinical data - Frequency of signs and symptoms; course of disease; Differential diagnosis; Death or sequelae rates Epidemiological data - Mode of occurrence; in time; By place; By population groups. Modes of transmission - Sources of infection; Routes of excretion and portal of entry; Factors influencing transmission Laboratory data - Isolation of agent(s); Serological confirmation; Significance of results Interpretation of data - Comprehensive future of outbreak; Hypotheses as to cause(s); Formulation and testing of hypotheses by statistical analysis . Control measures - Definition of strategies and methodology of implementation; Constraints; Results Evaluation - Significance of results; Cost effectiveness . e. MEASURES FOR CONTROL AND PREVENTION OF EPIDEMICS: Don't wait the end of the investigation. General measures as beginning. Specific measures according to the results.2) Kinds of measures to control The source (i.e. environmental measures). Eg- Chlorination of water or spraying insecticides. The transmission (Eg- Hygiene measures) The carrier(Eg- Recall a lot of suspected case) Reduce the susceptibility of host(Eg- Vaccination) Behavioral measure (Mosquito repellants)