All are true regarding point-source epidemic except?

Ans. is b i.e., Children are most commonly involved o The main aim of descriptive epidemiology is to study the distribution of disease in time, place and person. Time distribution o There are three kinds of time trends or fluctuations in disease occurence :? A. Sho term fluctuations epidemics B. Secular trends or long term fluctuations C. Periodic fluctuation Sho term fluctuation o The best known sho - term fluctuation in the occurence of a disease is an epidemic. o There are three major types of epidemics ? 1) Common - source epidemics a) Single exposure or point source epidemics b) Continuous or multiple exposure epidemics 2) Propagated epidemics 3) Slow (modern) epidemics Common source epidemics q As name suggests, the source of disease agent is common for all cases. q It is of two types. a) Single exposure or point source epidemics o The exposure to the disease agent is brief and essentially simultaneous --> single exposure. Because disease agent enters into all exposed persons at same time --> the resultant cases all develop within one incubation period of the disease. The epidemic curve rises and falls rapidly. Because exposure is single (simultaneous) with no fuher exposure ---> No secondary wave (no secondary case). Epidemic tends to be explosive, there is clustering of cases within a narrow interval of time. o Point source epidemics are mostly (not always) due to exposure to an infectious agent. Examples --> Food poisoning, Bhopal gas tragedy, Minamata disease in Japan, Chernobyl tragedy. b) Continous or multiple exposure epidemics o Exposure from the common (same) source is prolonged - continous, repeated or intermittent. o Exposure is not at the same time or place. o For examle, a prostitute may be a common source in a gonorrhea outbreak, but since she will infect her clients over a period of time there may be no explosive rise in number of case. Because disease agent enters into exposed person at different time --> outbreaks continues over more than one incubation period. o Example --> Outbreak of legionnaire's disease (respiratory illness) in 1976 in Philadelphia (USA).