A drug that reduces moality but does not cure a disease will gradually lead to
Correct Answer: Increase in prevalence no change in incidence
Description: Relationship between prevalence and incidence Prevalence 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= IxD (incidence x mean duration ) Example (for a stable condition) Incidence = 10 cases per 1000 population per year Mean duration of disease = 5 years Prevalence = 10 x 550 per 1000 population Conversely, it is possible to derive incidence and duration as follows: Incidence= P/D Duration = P/I The above equation (P = I x D) shows that the longer the duration of the disease, the greater its prevalence When we see a change in prevalence from one time period to another, this can result from changes in incidence, changes in duration of disease or both. For example, improvements in treatment may decrease the duration of illness and thereby decrease prevalence of a disease. But if the treatment is such that by preventing death, and at the same time not producing recovery, may give rise to the apparently paradoxical effect of an increase in prevalence. Fuher, if duration is decreased sufficiently, a decrease in prevalence could take place despite an increase in incidence. Ref: Park 23rd edition Pgno : 61
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