The early days…John Snow and the Broad Street Pump

1. The early days…John Snow and the Broad Street Pump

2. BaSiCsOF EpidEmioLoGy -Dr Preetam ‘08 BATCH

3. Definition of epidemiology • It is defined as “ study of distribution & determinants of health related states or events in a specified population, & application of this study to control of health problems”.

4. Aims of Epidemiology • Describe distribution & magnitude of health & disease • To identify etiological factors in pathogenesis of disease • To provide data for planning implementation & evaluation of services for the prevention control & treatment of diseases

5. Epidemiology Vs Clinical medicine. • Basic difference between epidemiology & clinical med is UNIT OF STUDY is ‘Defined population’ & case or ‘patient’ • Epidemiology is thus concerned with both sick and healthy. • Clinician statistician & epidemiologist • In clinical med the physician seeks a diagnosis from which he derives the prognosis & prescribes specific treatment

6. In epidemiology the epidemiologist has data from which he derives the aetiology & determines the disease trend and gives various control measures. • In clinical med the patient comes to the doctor in epidemiology the investigator goes to the communityto find risk factors or etiology.

7. Epidemiological Aproach • Asking Questions • Making Comparisons

8. Basic Measurements in Epidemiology • Measurements of Mortality • Morbidity • Disability • Natality • Measurements of demographic variables • Measurement of health care facilities, utilization of health services.

9. Tools of measurement • Rates • Ratios & • Proportions • Rates comprises of numerator denominator time specification and a multiplier Death rate=no of deaths in 1 yr/mid yr population* 1000 • Ratio- is relation in size between two random quantities. Wbc:rbc, sex ratio etc

10. Proportion • Is a ratio which indicates relation in magnitude of a part of the whole.

11. Types and sources of data • “Primary data”- data collected by an investigator in the field, through cross section or longitudinal survey. • “Secondary data”- data obtained from published or unpublished sources eg. Medical records , private practitioners & survey reports namely National Family Health Survey, Reproductive & Child Health Report, textbooks , journals, annual & other reports published by various health agencies.

12. Community Diagnosis • It is defined as “ process of appraising the health status of a community, including assembly of vital & other health related statistics & of information pertaining to determinants of health, such as prevalence of tobacco smoking & examination of these determinants of health in the specified community”.

13. The community diagnosis is based on collection & interpretation of the relevant data such as • Age & sex distribution of population by social groups. • Vital statistical rates such as birth rate & death rates. • The incidence & prevalence of the imp. Diseases of the area

14. Clinical vs Community Diagnosis

15. DISEASE TRENDS

16. Secular or long term trend • It implies changes in occurrence of disease over a long period of time generally several years or decades. • A secular trend implies a consistent tendency to change in a particular direction or definite movement in one direction eg coronary heart ds. , lung cancer & DM, which have shown a consistent upward trend. • And declining trend of T.B, typhoid, & diphtheria during past 50 yrs.

17. Cyclical trend • Some diseases occur in cycles spread over short period of time which may be days, weeks, months or years. • Eg- measles in pre-vaccination era appeared in cycles with major peaks every 2-3 yrs.

18. Seasonal trend • Seasonal variation is well known characteristic of many communicable diseases eg- URI increased during winter, GIT infections in summer & malaria during rainy season.

19. INVESTIGATION OF AN EPIDEMIC

20. Need for epidemic investigation • The primary objective of an epidemic investigation is to control the outbreak, limit its spread to other areas & assess how preventive strategies can be further strengthened to reduce or eliminate the risk of such outbreaks in future.

21. Diseases requiring investigations • Endemic diseases with the potential of causing focal or large outbreaks eg- malaria , cholera • The diseases for which eradication or elimination goals have been set. A single case such disease should be treated as an outbreak eg- polio, guinea worm. • Rare but internationally important diseases with higher case fatality rates eg- yellow fever.

22. Definition of an Outbreak • An outbreak or epidemic is defined as the occurrence in a community of an illness clearly is excess of expected numbers. • Outbreak is usually limited to a small focal area, an epidemic covers larger geographic areas & has more than one focal point

23. The number of cases which is exceeded to be called an outbreak, varies according to several factors. It depends on past historical patterns of the disease , case fatality, complication rates & potential for spread to other areas • For some diseases even a single case (polio, guinea worm) constitutes an outbreak.

24. Warning signals for outbreak • Clustering of cases of deaths in time and / or space. • Unusual increase in deaths. • Acute hemorrhagic fever. • Acute fever with altered sensorium, renal involvement. • Acute flaccid paralysis in a child. • Even a single case of measles or any other epidemic prone disease from a tribal or other poorly accessible area. • Natural disasters.

25. Steps of Investigation • Verification of diagnosis by- • Clinical examination • Lab. Diagnosis.

26. 2. Confirmation of the existence of an epidemic by – • Cases finding through active surveillance & community surveys. • Visits or telephonic calls to the medical facilities or priv. pract. , NGOs • Active surveillance should be maintained even after the outbreak is over • House to visits.

27. 3) Line listing ,defining & counting of cases

28. Data analysis with respect to time place & person. • Formulation of hypothesis • Evaluation of ecological factors • Further evaluation of population at risk. • Writing a report

29. Surveillance

30. Surveillance is data collection for action. Surveillance data are required for planning disease activities & for evaluating impact . • Disease surveillance data are also required to identify high risk areas or high risk case specific & other groups who require special attention. • Early warning signals will be missed in the absence of an effective surveillance system.

31. To plan any disease control prog. It is imp. To know the following- • Who get the diseases • How many get them. • Where they get them • When they get them • Why they get them

32. Steps in surveillance procedure- • Collection of data • Compilation of data • Analysis & interpretation • Follow up action • Feedback

33. Prerequisites for effective surveillance- • Use of standard case definition • Ensuring regularity of reports • Action on the reports

34. Methods of data collection • Sentinel surveillance • Active surveillance • Vector surveillance • Laboratory surveillance • Sample surveys • Outbreak investigations • Special studies

35. Sentinel surveillance • A hospital, health center, lab. Rehabilitation center which caters to a relatively large number of cases of the disease, can be considered as sentinel center. It can provide information on one or more disease. • Sentinel center helps in providing • Line lists of cases of selected diseases. • Early warning signals which trigger action for outbreak investigation.

36. Active surveillance • Done under following circumstances- • During outbreaks to determine its extent &keep mortality rates by initiating early T/t. • As the number of cases of disease decline to negligible level it becomes important to receive info. On every single case so that future transmission is interrupted. Eg-AFP

37. Vector surveillance Important to monitor the existing factors. Increase in density of vector on their breeding site should be taken as early warning signals for vector borne outbreak Eg- the clues mosquitoes breed in dirty water whereas anopheles prefers clean water for breeding.

38. Laboratory surveillance Testing water samples for coliform organisms is a measure to determine the risk of water borne outbreaks. Checking the chlorination level of water is also important especially during monsoon & post monsoon period.

39. IDSP • IDSP is a decentralized, state based surveillance programme in the country. • Launched in 2004 by Ministry of Health and Family Welfare with World Bank assistance. • Intended to detect early warning signals of impending outbreaks. • Helps to initiate an effective response in a timely manner. • Also expected to provide essential data to monitor progress of on-going disease control programmes • All the outbreaks cannot be predicted or prevented . But precautionary measures can be taken within the existing health infrastructure and service to reduce the outbreaks

41. Diseases and core condition under IDSP Regular Surveillance∗: • Vector Borne Disease : 1. Malaria • Water Borne Disease : 2. Acute Diarrhoeal Disease (Cholera) : 3. Typhoid : 4. Jaundice • Respiratory Diseases : 5. Tuberculosis : 6. Acute Respiratory Infection • Vaccine Preventable Diseases : 7. Measles • Diseases under eradication : 8. Polio • Other Conditions : 9. Road Traffic Accidents (Linkup with police computers) • Other International commitments : 10. Plague, Yellow fever • Unusual clinical syndromes : 11. Menigoencephalitis/ Respiratory (Causing death/hospitalization) Distress, Haemorrhagic fevers, other undiagnosed conditions

42. Types of Surveillance in IDSP 1. Syndromic– Diagnosis made on the basis of symptoms/clinical pattern by paramedical personnel and members of the community. 2. Presumptive (Clinical) – Diagnosis made on typical history and clinical examination by Medical Officers. 3. Confirmed(Laboratory) – Clinical diagnosis confirmed by an appropriate laboratory test.