Serological evidence of Cryptosporidium infections in southern Europe.

Although cryptosporidiosis outbreaks have been frequently reported in the United States, Canada and the United Kingdom, few outbreaks have been reported on the European continent. The reasons for this are unclear. To ascertain whether a European population has been previously exposed to Cryptosporidium, we conducted a survey of 100 resident blood donors in a northern Italian city for IgG serological response to two oocyst antigen groups. A serological response to the 15/17-kDa antigen group was detected in 83% of blood donors and response to the 27-kDa antigen group in 62%. Donors who traveled outside of Italy during the prior 12 months were less likely to have had a response to the 15/17-kDa antigen group (p < 0.04) and to have a less intense response (p < 0.05). Older age was predictive of a more intense response to each antigen group (p < 0.01). The fraction of Italian blood donors with a serological response to either antigen group was higher than in four United States blood donor populations, with differences more pronounced for response to the 15/17-kDa antigen group (p < 0.01). A lower fraction of Italian donors had a serological response to either antigen group than persons tested at the time of a cryptosporidiosis outbreak in the United States or blood donors tested six months after that outbreak (p < 0.05). Since the presence of serological responses to these antigen groups predicts a reduced risk of cryptosporidiosis, the high prevalence of serological responses in these Italian blood donors may explain the infrequent occurrences of clinically detectable cryptosporidiosis in this city.