Serological analysis of a cryptosporidiosis epidemic

Background A cryptosporidiosis epidemic occurred among residents and visito rs to Colling-wood, Ontario, during March 1996. Fifty-five per cent of 36 c onfirmed cases were Collingwood visitors and 57% of Collingwood resident ca ses were under 10 years of age. The low level of reported diarrhoeal illnes s among adult Collingwood residents caused government officials and physici ans to question whether an epidemic had occurred in Collingwood. Methods To better evaluate the extent of the epidemic, anonymous surplus se ra from 89 adult Collingwood residents, collected for routine tests prior t o, during and after the epidemic, and from 80 adult Toronto residents were tested using a Western blot assay for Ige antibody response to two Cryptosp oridium antigen groups (15/17-kDa and 27-kDa). Results For sera collected from 1 January 1996 to 17 June 1996, a higher fr action of Collingwood residents had a detectable serological response (P < 0.002) and the mean intensity of serological responses was higher for Colli ngwood than Toronto residents (P < 0.001). The mean intensity of serologica l responses for Coiling wood residents was higher in specimens drawn during the 8 weeks following the initial case reports compared to those drawn bef ore or after this period (15/ 17-MDa, P < 0.02; 27-kDa, P < 0.10). Conclusions These elevated serological responses indicate that Cryptosporid ium infections among Collingwood residents likely occurred more commonly th an illness reports suggested, consistent with a community-wide cryptosporid iosis epidemic. Similar studies should be considered in future suspected cr yptosporidiosis epidemic investigations.