Epidemiological features of pneumonic plague outbreak in Himachal Pradesh, India.

Four people admitted to a tertiary care hospital during February 2002 had similar respiratory symptoms; they belonged to one family residing in a village in Himachal Pradesh, India. The clustering of these cases in space and time led to the suspicion that it could be a pneumonic plague outbreak. A standard case definition, and treatment and prophylaxis guidelines were prepared. Active surveillance identified 30 cases. The incubation period ranged from 3 to 7 days. Among the affected people, 53.3% were males, and 90% were >15 years of age. Fever with cough was the most common presenting feature (43.3%). The diagnosis of pneumonic plague was confirmed from blood cultures using conventional biochemical tests, phage susceptibility of the identified organisms, and F1 antigen ELISA and PCR for the pla gene. Five patients died giving a case-fatality ratio of 16.6%. The other cases recovered following treatment. Early identification of cases and prompt institution of control measures, particularly among close family members, relatives and health care contacts is essential for containing outbreaks. To prevent future outbreaks, known endemic foci should be identified and essential information should be gathered on the epizoology of plague.