[An outbreak of human orf disease caused by introduced black goats]

To identify risk factors for a human orf disease outbreak in a village in Chongqing city.

Standardized case-definition was set and a case-finding program was conducted among all the residents of the village. All the patients were interviewed using a standardized questionnaire and collected fluids in the skin rash for laboratory testing. A retrospective cohort investigation was conducted among all the village residents who introduced the black goats to analyze the risk of orf infection, in relation to the mode and frequency of contacts to the infected goats.

We found 18 cases (including 16 suspected cases and 2 confirmed cases) among the members of 10 families that introduced the black goats. Village residents who had ever used their legs to grip the goats were nearly five times as likely to develop orf disease as those who did not (RR = 4.98, 95%CI: 1.34 - 75.27). Village residents who had ever washed and wiped the goats were three times as likely to develop orf disease as those who had not (RR = 3.09, 95%CI: 0.98 - 45.38). The frequency of contacts with the infected goats was associated with the risk of developing orf disease in a dose-response fashion (χ² test for trends: P = 0.006). Frequently wearing long trousers when dealing with the goats appeared as a protective factor (RR = 0.30, 95%CI: 0.15 - 0.78).

This outbreak was caused by the introduced black goats which carried and infected by the orf virus. Direct physical contact with infected goats but without wearing protective clothing were risk factors for the development of human orf disease.