Epidemiology by alicejenny



    Unit 1:
What is it about?

• Distribution, frequency and determinants of
  health problems and diseases in human
• Aim: obtain, interpret and use health
  information and reduce disease burden
• Practical interventions and programmes
        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
   ects causing illness, health problems or death in a
   community or region?
    Seven uses of epidemiology cont.
3.Look at risks of individuals as they affect groups or
-What are the risks factors,problems,behavoiur that
   affects group?
-Risk factor assessment done: health screening,
   medical exams, disease assessments.
-How well do public health and health services meet
   the problems and needs of the population or group?
    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
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
         Types of epidemiology
• Descriptive epidemiology p.9
  – What and frequencies
  – Who
  – Where
  – When
  It looks at disease distribution and frequency
• Analytic epidemiology p.9
  – Analyze causes
  – How? Process
  – Why? Relationship of variables
• Intervention or experimental epidemiology
   – Effectiveness of new methods/interventions
   – Improved underlying conditions
   – E.g. case-control studies; cohort studies
• Evaluation epidemiology p.9
   – So what?
   – Any improvement?
   – What facilitated the change?
     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.
                 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.
              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.
               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.
                  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:
           Measuring frequency
•   Incidence
•   Prevalence
•   Defined time period
•   Population at risk
•   P.12
              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
              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
            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
• COVERAGE: p.139-142
-a measure always expressed as %,
-comparison of those who used the services
  with those who should have used services.
     Incidence and Prevalence rates
• Decide what are you counting?
   – Episodes, people, attendance or what?
• What the service count when filling monthly
• 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
• 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
                  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
                 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
             Why use rates?
• To make comparison
• To calculate the number of expected cases in a
  specific time frame/period
               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
• E.g. can be used directly to measure health status
  by IMR (infant mortality rate).
• Indirect: socioeconomic status IMR
• P.17
            Why indicators?
• Analyze the present situation
• Make comparison
• Measure changes over time e.g. IMR, MMR,
  nutritional disorders
• P.17
     WHERE to access information?
•   Birth and death registers
•   Health statistics
•   Routine HIS
•   Population census
•   Surveillance
•   Investigations of epidemics
•   Sample surveys p.18
             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
           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
     Define the following & identify
•   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
     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.
    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

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