This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'All are true for Point source epidemic except: \nSelect and explain. \nA. Person-to-person transmission, B. Clustering of cases within a short period of time, C. Epidemic curve rises and falls sharply, D. All cases usually develop within one incubation period', 'role': 'user'}, {'content': 'Answer: A \nExplanation: EPIDEMIC:\n\nDefinitions of epidemic:\n\n– Occurrence of no. of cases of a disease ‘clearly in excess of normal expectancy (NE)’\n\nNormal expectancy is derived by looking at average of no. of cases of the disease in previous 3 – 5 years in that geographical area\nIf NE = zero, ‘even one case is considered epidemic’\n\n– Statistically speaking, epidemic is when no. of cases ‘exceed twice the standard deviation’\nNo. of cases > Mean + 2SD ( >μ + 2σ)\n– Occurrence of a new disease in a population (as NE = Zero)\n– Reoccurrence of an eliminated/ eradicated disease in a population (as NE = Zero)', 'role': 'assistant'}]