Uses of epidemiology and investigation of an epidemic

Department of Community Medicine, BMC Sagar

1. USES OF EPIDEMIOLOGY AND INVESTIGATION OF AN EPIDEMIC GUIDED BY- PRESENTED BY- Dr. Rupesh Sahu Dr. Shefali Jain Assistant professor (P.G. 1 ST year) Dr. Rakesh Mahore Assistant professor

2. INTRODUCTION Epidemiology is the basic science of public health Health science that describes health and disease associations in populations rather than in individuals Information is essential for the formulation of effective public health initiatives to prevent disease and promote health in the community.

3. USES OF EPIDEMIOLOGY 1.Describe the spectrum of the disease: Disease represents the end point of a process of alteration of the host’s biological systems. Measles, can cause a variety of disease end points. Example, the majority of infections with rubeola (measles) virus result in the classical febrile, blotchy-rash disease, rubeola virus can also cause generalized haemorrhagic rash and acute encephalitis. Years after initial infection, rubeola can also cause subacute sclerosing panencephalitis (SSPE).

4. 2.Describe the natural history of disease: example, cohort studies of individual having HIV, revealed that a drop in the level of T lymphocytes having the CD4 marker was associated with being infected with HIV, and further CD4 causes clinical symptoms of AIDS. This observation stimulated immunologists to focus their research on the interaction of the immune system and HIV.

5. 3.Community diagnosis: Identification and quantification of current health problems, risk factors prevalent in the community, and assessment of available resources are required to prioritize appropriate intervention. Example: epidemiological survey in one area of China identified the epidemic of HIV due to plasma donations in villages.

6. 4.Describe the clinical picture of a disease: Studying the occurrence of clinical phenomena and its distribution in the community help epidemiologist to identify disease syndromes. Epidemiological strategies can identify who is likely to get a disease such as Rheumatic Heart Disease, the characteristic symptoms and signs, the extent of the epidemic, the risk factors, and the causative agent, and can help to determine the effectiveness of treatment and control efforts.

7. 4.Identify factors that increase or decrease the risk of acquiring disease Knowing these risk factors can often provide public health professionals with the necessary tools to design effective programmes to intervene before disease occurs. For example, Every study shows that smoking is the biggest single risk factor for ill health, because it is a major risk factor for cardiovascular disease, chronic respiratory disease, and many cancers (e.g. of the lung, nasopharynx , and bladder). Therefore, statutory warning is given to aware consumers regarding ill effect of smoking.

8. Identify precursors of disease and syndromes : For example; High blood pressure, a treatable condition, has been identified through case–control and cohort studies as a precursor to heart disease, stroke, and kidney disease. So, preventive measures can be taken to control high blood pressure.

9. Test the efficacy of intervention strategies: vaccine or other intervention programme must be proven effective and safe before it is used in the community. typhoid vaccine provided some protection against small infecting inocula , but the frequency of unpleasant side effects with the whole-cell vaccines and the need for multiple injections in the past influenced many people against being vaccinated. So, here the ‘public health effectiveness’ of the vaccine will be very low.

10. Investigate epidemics of unknown aetiology : Epidemiological strategies were used to establish the extent, cause, modes of transmission, and risk factors for Ebola haemorrhagic fever, which first occurred in the Congo in 1976 by appropiate use of epidemiological approach and statistical methods.

11. Evaluate public health programmes : Departments of health are engaged in a variety of activities to promote the health of the community, ranging from surveillance and vaccination programme to clinics for the treatment of specific diseases. For example, most countries have establish sexually transmitted infections (STI) clinics, but studies in Thailand and Beijing have demonstrated that the majority of the patients with STIs do not attend the government STI clinics.

12. Elucidate mechanisms of disease transmission: It helps public health professionals to protect the public by stopping transmission of the disease agent. For example, public health efforts in California to prevent western equine encephalitis have concentrated on control of the mosquito vector and vaccination of horses, which are a reservoir of the virus. So, that transmission of virus couldn’t occur.

13. Elucidate the molecular and genetic determinants of disease progression: For example: Epidemiological strategies helped to elucidate the changes in the human immune response by CD4 and CD8 cells that accompany infection and disease progression by disease agents and genetic factors (such as CCR5 absence or heterozygosity ) that prevent HIV infection and slow progression of HIV disease.

14. Implementation science The scientific community and policymakers have recognized the slow rate at which scientific advances are translated into public health policies and medical and public health practice. Thus, there is growing support for identifying and testing strategies that will speed up the process of translating science into action and practice.

15. Introduction to principles of outbreak investigation Outbreaks can occur anywhere, from a very remote area where no health facility exists to nosocomial outbreaks in a very sophisticated hospital where hundreds of health personnel are employed. Outbreak investigations provide the opportunity to discover new aetiological agents, to understand factors that promote the spread of the diseases, and to identify the weaknesses of existing prevention and health programmes .

16. Outbreak or Epidemic? The terms outbreak and epidemic can be used interchangeably. Some epidemiologists prefer to use the term epidemic only in a situation that covers a very wide geographical area and involves large populations. Outbreak is used for a new emerging disease or situation when an endemic disease or health events occur at a greater frequency than normally expected within a specified period and place.

17. example, ‘outbreak of HIV’: describe a sharply increasing HIV prevalence rate among commercial sex workers in a city where the normal rate was low in the previous year. ‘HIV epidemic’ : an abnormally high HIV prevalence is found among sex workers in many cities of the country.

18. Non-communicable outbreaks such as mass sociogenic illnesses are sometimes reported as acute outbreaks of unexplained illness. Example: Following a fire in a pub on New Year’s Eve 2009 in Thailand, an unprecedented number of 67 deaths and 153 hospitalizations resulted. Ex: Bhopal gas tragedy outbreak.

19. The criteria for judging that an outbreak has occurred can be one of the following : The occurrence of a greater number of cases or events than normally occurs in the same place and during the same period as in past years. 2. A cluster of cases of the same disease occurs that can be linked to the same exposure.

20. Here, The term cluster means aggregations of relatively uncommon events or diseases in space and/or time in amounts that are believed or perceived to be greater than could be expected by chance 3. A single case of disease that has never occurred before or might have a significant implication for public health policy and practice can be judged as an outbreak that merits investigation.

21. How can an outbreak be detected? Health personnel Laboratories Official disease notification systems Newspapers and media Village health volunteers

22. Purposes of outbreak investigation: Controlling the current outbreak Research to provide knowledge of the disease Evaluation of the effectiveness of prevention programmes Prevention of future outbreaks Evaluation of the effectiveness of the existing surveillance system Training of health professionals Responding to public, political, and legal concerns

23. Components of an investigation team Field epidemiologist Disease control specialists Laboratory technicians Specialists in particular areas (e.g. veterinary medicine) Public health administrators

24. Issues to be considered before implementing an investigation Assessing the existence of the outbreak Gathering available basic information Ensuring that clinical specimens and suspected materials are collected in a timely and appropriate manner Obtaining permission and adequate support from local and national authorities Planning the field operation

25. Steps of outbreak investigation 1. Confirm the existence of the outbreak . Investigators should review the number of cases with the local health officers or hospital staff and compare it with the number found during the same period recorded in past years.

26. 2 . Verify the diagnosis and determine the aetiology of the disease. For example, many adults in a remote village were ill with fever, muscle and joint pain, rashes, etc If the diagnosis and aetiology of the disease is unknown, the local public health officials will find it very difficult to educate the public or implement effective preventive programmes . For confirmation, serology of patients must have sharply rising immunoglobulin M ( IgM ) antibodies to dengue virus.

27. 3 . Develop a case definition, start case finding, and collect information on cases. Develop an appropriate case definition Active case finding Collecting information on cases Identifying information Demographic information Clinical information Suspected risk factors

28. 4. Describe persons, places, and times, and generate hypotheses. In this step, investigators need to answer the following questions: 1. What are the main clinical features? 2. What population(s) is at risk? 3. What are the risk factors? 4. What are the most likely explanations of how the outbreak began?

29. 5. Test the hypotheses using an analytic study. In an outbreak of infectious disease, the investigator needs to answer the following questions: 1. What is the aetiology of the disease? 2. What is the source of infection? 3. What is the pattern of spread? 4. What are the risk factors for an individual to get the disease? 5. What are the determinants of the outbreak or the factors which, when combined together, result in the outbreak?

30. 6 . Carry out necessary environmental or other studies to supplement the epidemiological study. In an outbreak of unknown illness in a rural village of Egypt, cases developed severe abdominal pain, persistent vomiting, and generalized weakness, T he investigator was able to detect abnormally high blood lead levels among the cases. The analytical study revealed an association between high lead levels in the blood and eating flour from a particular mill factory.

31. T he investigators noted a lead smelting pot in the corner of the mill. Lead was used by the miller to attach the crosspiece to the grinding stone. Occasionally the lead would break off and contaminate the flour. The miller reported using about 2 kg of lead per year. Analysis of grain from the mill showed no lead; however, lead was found in flour from the surface of the mill stone and in samples of flour after grinding was complete

32. 7. Draw conclusions to explain the causes or the determinants of the outbreak, based on clinical, laboratory, epidemiological , and environmental studies. Laboratory evidence: The aetiology of the disease is identified in the patients and in the suspected source of infection. If the investigator cannot identify the aetiology from the suspected source, it is still possible to use certain markers to support their conclusions. a Vibrio cholerae type O1 could not be cultured from the drinking water supply of the affected community, the observation of human faecal coliform bacteria in the water helped to indicate that human faeces had contaminated the water.

33. Clinical evidence: In the SARS outbreak, most patients developed atypical pneumonia, with rapid progression to respiratory failure, and a fraction of them also had diarrhoea , which could be explained by the findings of SARS coronavirus both in the respiratory tract and stools of patients. Environmental evidence: For an outbreak of food poisoning, a cooking environment that is dirty or located close to the toilet is convincing evidence of food being contaminated by faeces . Crowding in bedrooms is very convincing evidence for a respiratory tract disease outbreak.

34. Epidemiological evidence: Epidemiological evidence found in the descriptive and analytical studies should clearly explain the following aspects: ♦ Pattern of spread, as described by an epidemic curve. ♦ Statistical strength of association between exposure and developing the disease. ♦ Dose–response relationship, which demonstrates a higher strength of association when the exposure is increasing. ♦ Exposure should precede an illness.

35. 8. Report and recommend appropriate control measures to concerned authorities at the local, national, and if appropriate, international levels. The investigators need to complete two tasks before leaving the outbreak area: 1. Complete analysis and data interpretation 2. Present the main findings with recommendations

36. What can be done to control the outbreak? With timely investigation, some interventions can be implemented to stop further spread. In the outbreak of measles in a rural community in Peru, measles vaccines were given to children aged between 6 months and 15 years who were not measles cases, regardless of their previous immunization status. Using knowledge about the complication of measles in previous studies, the investigators estimated that the action prevented 87 cases of diarrhoea and 46 cases of pneumonia, and averted five deaths

37. How to prevent future outbreaks? In many instances, interventions cannot be implemented for the current outbreak, but the findings can be used to set up new practices or policies. For example, The Egyptian government, after reviewing the results of the investigation of lead contamination in flour mills, agreed to ban the use of lead in privately owned flour mills

38. How to improve the investigation? The investigator should review the performance of the investigation and identify the weaknesses of the methodology or the field operation so that improvements can be made.

39. How to improve surveillance The best time to evaluate the surveillance system is during an outbreak investigation. In most outbreaks, the investigator must review data from existing surveillance systems. With this direct involvement, the investigator will be able to evaluate the timeliness, completeness, validity of diagnosis, sensitivity of the system, and utilization of the surveillance information.

40. 9. Communicate the findings to educate other public health professionals and the general public. The information will raise the awareness of health and government authorities to assess their own situation and implement measures to prevent possible outbreaks. Dissemination of information should occur in a timely manner through weekly or monthly reports. Before releasing the investigation results through the media, the investigator must ensure that all the facts are delivered in a constructive manner and do not result in blame of any organization.

41. The investigator should also report the investigation results in an international journal or bulletin such as The Weekly Epidemiological Record of the WHO, The Morbidity and Mortality Weekly Report of the US CDC, The Eurosurveillance of the European Centre for Disease Prevention and Control, Or, the epidemiological bulletin of their own country.

42. 10. Follow up the recommendations to ensure implementation of control measures. The investigator should follow up the investigation by maintaining close communication with local health authorities. An absence of new cases for at least two incubation periods of the infectious disease under investigation could suggest that the outbreak is subsiding. The investigator should learn the reasons why the recommendations were or were not implemented. If the recommendations were implemented, the investigator can also learn the impact by observing the trend of the disease.

43. Cooperation for international outbreak investigation and preparedness The world today is especially prone to outbreaks because of frequent cross-border movement, civil war and migration, rapid transportation, international trading, tourism, etc. It is important for each country to build up its capacity for surveillance, outbreak preparedness, and investigation.

44. In addition to the US CDC Epidemic Intelligence Services, over 50 countries have started training programmes and established a medical detective unit that is ready to investigate all kinds of outbreaks. These training programmes are known by different names, such as the Field Epidemiology Training Program (FETP) the Field Epidemiology and Laboratory Training Program (FELTP) The European Programme for Intervention Epidemiology Training (EPIET).

45. The WHO has supported the establishment of the Global Outbreak Alert and Response Network, a technical collaboration of existing institutions and networks to pool human and technical resources for the rapid identification, confirmation and response to outbreaks of international importance.

46. REFERENCES K. Park , Park’s Textbook Of Preventive And Social Medicine, M/S Banarsidas Bhanot Publishers, 25 th Edition,2019 Roger Detels Et Al, Oxford Textbook Of Global Public Health, Oxford, 6 th Edition

47. THANK YOU