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. Epidemic curve rises and falls sharply, B. Clustering of cases within a short period of time, C. Person-to-person transmission, D. All cases usually develop within one incubation period', 'role': 'user'}, {'content': 'Answer: C \nExplanation: EPIDEMIC:\n• Definitions of epidemic:\n– Occurrence of no. of cases of a disease ‘clearly in excess of normal expectancy (NE)’\n1. Normal expectancy is derived by looking at average of no. of cases of the disease in previous 3 – 5 years in that geographical area\n2. If NE = zero, ‘even one case is considered epidemic’', 'role': 'assistant'}]