Epidemiology

1. Epidemiology Unit 1: What is it about?

2. Definition • Distribution, frequency and determinants of health problems and diseases in human populations • Aim: obtain, interpret and use health information and reduce disease burden • Practical interventions and programmes

3. Seven uses of epidemiology 1.To study the history of disease: -Trends of a disease for the prediction of trends. -Result are useful in planning for health services and public health. 2.Community diagnosis: -What are the diseases,conditions,injuries,disorders,disabilities,defects causing illness, health problems or death in a community or region?

4. Seven uses of epidemiology cont. 3.Look at risks of individuals as they affect groups or population. -What are the risks factors,problems,behavoiur that affects group? -Risk factor assessment done: health screening, medical exams, disease assessments. 4.Assessments,evaluation,research. -How well do public health and health services meet the problems and needs of the population or group?

5. Seven uses of epidemiology cont. 5.Completing the clinical picture: -Identification and diagnosis process to establish that a condition exists or that a person has a specific disease. 6.Identification of syndromes: Help to establish and set criteria to define syndromes. 7.Determine the causes and sources of disease: -Findings allow for control,prevention,and elimination of the causes of disease,conditions,injury,disability d

6. Types of epidemiology • Descriptive epidemiology p.9 • What and frequencies • Who • Where • When It looks at disease distribution and frequency

7. Analytic epidemiology p.9 • Analyze causes • How? Process • Why? Relationship of variables

8. Intervention or experimental epidemiology p.9 • Effectiveness of new methods/interventions • Improved underlying conditions • E.g. case-control studies; cohort studies

9. Evaluation epidemiology p.9 • So what? • Any improvement? • What facilitated the change?

10. Concepts and their application • Incidence: the number of new cases, episodes or events occurring over a defined period of time, commonly one year. • Prevalence: the total number of existing cases, episodes or events occurring at one point in time, commonly on a particular day.

11. Concepts cont • Case: A person who is identified as having a particular characteristic such as a disease,behaviour or condition. Cases may be divided into possible, probable, and definite, depending on how well specific criteria are satisfied.p.18 • Controls: disease control programmes all to lower the incidence of new cases, or reduce the proportion of severe cases through treatment, to an acceptable low level, so that the disease is no longer considered a major public health hazard.

12. Concepts cont. • Catchment area: the geographical area from which the people attending a particular health facility come. • Catchment population :People attending particular health facilities • Case Fatality rate:the percentage/proportion of persons contracting a disease who die from it in a specified time period. This rate is usually used for communicable diseases.

13. Concepts cont. • Population at risk: is vital to know about all people at risk of developing a disease or having a health problem, as well as those who are currently suffering from it.

14. Concepts cont. • Epidemic: the occurrence in a community or region of cases of an illness or other similar event clearly in excess of what is normally expected. The characteristics of the illness, the area and the season all have to be taken into account. • Epidemic incidence curve: a graph that plots cases of the disease by the time of onset of the illness .An essential part of the analysis. This graph can indicate the nature of the outbreak and the probable source. • The types of epidemic incidence curves:

15. Measuring frequency • Incidence • Prevalence • Defined time period • Population at risk • P.12

16. When calculating • Numerator (number of cases/episodes) • Denominator (total population at risk) • Factor (e.g. 100, 1000, 10 000) • Time period (dates, weeks, month or years) • Use rates: incidence rates p.14 • Prevalence rates p.14

17. When calculating Incidence rate =new cases in specified period of time x factor total population at risk Prevalence rate =existing cases at the specified point of time x factor total population at risk

18. Coverage achieved • Know the total population groups e.g. children, pregnant women etc. • Know those who use the services • Plus those who are supposed to use it TOTAL POPULATION • COVERAGE: p.139-142 -a measure always expressed as %, -comparison of those who used the services with those who should have used services.

19. Incidence and Prevalence rates • Decide what are you counting? • Episodes, people, attendance or what? • What the service count when filling monthly statistics • E.G. DIARRHEA OR MALARIA – people get repeated attacks in one month and attend your service • This is one person sick but has suffered several times separate episodes in one year and attended your service several times

20. Prevalence: chronic conditions/ diseases – count the total number of sick people • Incidence: count episodes • To study the use of health services, information on – new attendance and repeat attendance are required

21. Defining a case • Know what are you referring to • E.g. Malaria case • Fever -Headaches • Body and joint aches • Rigors Treat as such BUT The MoHSS only base their case on lab. results Establish diagnostic criteria and classify as locally allowed

22. Case definitions • A case definition: is a standard set of criteria for deciding whether individual should be classified as having the health condition of interest. • Confirmed case:A case confirmed by an appropriate laboratory test. • Probable case:A case with typical clinical features of the disease without laboratory confirmation. • Possible/suspect case:A case with fewer of typical clinical features

23. Why use rates? • To make comparison • To calculate the number of expected cases in a specific time frame/period

24. Health Indicators • A measure that can be used to help describe a situation that exist and • To measure changes or trends over a period of time • Most are quantitative in nature but some more qualitative • E.g. can be used directly to measure health status by IMR (infant mortality rate). • Indirect: socioeconomic status IMR • P.17

25. Why indicators? • Analyze the present situation • Make comparison • Measure changes over time e.g. IMR, MMR, nutritional disorders • P.17

26. WHERE to access information? • Birth and death registers • Health statistics • Routine HIS • Population census • Surveillance • Investigations of epidemics • Sample surveys p.18

27. Types of Indicators • Health Policies e.g. statements, written plans, resource allocation • Social and economic development e.g. school enrolment, employment rates • District populations e.g. age and sex structure, birth and death rates etc. • Provision of health care e.g. access to services, coverage, h/w ratio to populations • Health status p.18-19

28. Health status indicators • Grouped in three categories • Nutritional status: LBW, malnutrition • Morbidity indicators: disease specific incidences • Mortality indicators: • IMR • MMR • CMR • Crude death rates of all ages etc. • P.19

29. Define the following & identify sources • Crude birth rate (CBR) • Total birth rates (TBR) • Crude death rates (CDR) • Infant mortality rate (IMR) • Maternal mortality rate (MMR) • Child mortality rate (CMR) • P.23-24

30. Rates and how to calculate? • Mortality rates p.41 • Morbidity rates p.41 • Coverage rates of e.g. FP,EPI,(what denominator to use) • Drop –out rates e.g.EPI,FP,TB,ARV, etc.

31. Calculate target populations within the catchment populations(high risk population groups). • E.g. • < 1yr • < 5yrs • Women of childbearing age • Old people-chronic diseases • Some workers-working with machinery and dangerous chemicals, construction workers • P.138