Epidemiological and clinical studies on an outbreak of trichinosis in central China

An outbreak of trichinosis occurred in the city of Zhengzhou, central China, between December 1995 and February 1996, affecting 85 of the administrative units into which the city is split. Of 297 subjects from eight of the affected units, 54% were seropositive for Trichinella and 41% had symptoms consistent with acute trichinosis. Of the 490 subjects who had eaten at one particular dumpling restaurant 1-5 weeks before the outbreak and who were traced, 291 (59%) were seropositive and 212 (43%) had been or were ill. MOst of the infections were in manual workers, cadres and merchants aged 20-49 years. Most of those who had been infected failed to develop gastro-intestinal symptoms or a cutaneous rash. Eyelid oedema was only seen in the early stages of the infection, the main clinical manifestations being fever of long duration of tiredness. Surprisingly, six cases had no marked symptoms after repeated infection. Eosinophilia (eosinophils > 7% of leucocytes) was noted in 71 (55%) of the 130 cases in which blood cells were counted. When 212 sera were tested for antibodies to Trichinella, seropositivities were found to increase from 89.1% (IFAT) of 87.7% (microprecipitation test) at presentation to 100% (both tests) 1 week after treatment with albendazole. All those treated were cured. The outbreak was one of the most extensive, single-source outbreaks ever recorded in China, probably with > 600 infections and > 300 clinical cases. The entire episode was attributed to the ingestion of undercooked pork dumplings at one restaurant.