Incidence of a disease is 4 cases per 1000 of population per year with duration of 2 years. Calculate the prevalence?
(A) 8/1000Prevalence = (Incidence Rate) x (Average Duration of Disease)/1000=4x2/1000=8/1000-P=I+D-= Incidence x mean duration-Incidence = 4 cases per 1000 population per year-Mean duration of disease = 2 years-Prevalence =4x2=8 per 1000 population[?]Relationship Between Incidence & Prevalence:oPrevalence varies directly with both incidence & durationoIf incidence is low, but duration is long (chronic), prevalence will be large in relation to incidence.oIf prevalence is low because of short duration (due to recovery, migration or death), prevalence will be small in relation to incidence. DIFFERENCE BETWEEN INCIDENCE & PREVALENCECharacteristicsWhat is measuredTime of disease diagnosisPeriod of timeDenominatorIncidenceRapidity of disease occurrenceNewly diagnosedPeriod of study that allows monitoring disease occurrencePopulation at riskPrevalenceProportion of population with diseaseSurviving cases diagnosed at any timeSpecific timeWhole population[?]PREVALENCEoThe term "disease prevalence" refers specifically to all current cases (old and new) existing at a given point in time, or over a period of time in a given population.oA broader definition of prevalence is as follows: "the total number of all individuals who have an attribute or disease at a particular time (or during a particular period) divided by the population at risk of having the attribute or disease at this point in time or midway through the period".oAlthough referred to as a rate, prevalence rate is really a ratio.oPrevalence is of two types:-Point prevalence-Period prevalenceoPrevalence depends upon 2 factors, the Incidence and duration of Illness. Given the assumption that the population is stable, and incidence and duration are unchanging, the relationship between incidence and prevalence can be expressed as:P=IxDPrevalence = Incidence x mean durationoExample (for a stable condition)oIncidence = 10 cases per 1000 population per yearoMean duration of disease = 5 yearsoPrevalence =10x5 50 per 1000 populationoConversely, it is possible to derive incidence and durationoas follows:oIncidence P/DoDuration =P/IoUses of prevalence-Prevalence helps to estimate the magnitude of health/disease problems in the community, and identify potential high-risk populations-Prevalence rates are especially useful for administrative and planning purposes, E.g., Hospital beds, manpower needs, rehabilitation facilities, etc.
8/1000
4/1000
2/1000
6/1000
Epidemiology