A two-year follow-up survey of antibody to Cryptosporidium in Jackson County, Oregon following an outbreak of waterborne disease

To estimate the duration of Cryptosporidium-specific antibody, a Western blot assay measured antibody in paired sera from 124 residents of Jackson County, Oregon collected 0·5 and 2·5 years after the end of an outbreak in Talent, Jackson County. The outcome measure was the intensity of antibody responses, (which may approximate to a titre), to 27-kDa and 15/17-kDa antigens. Intensity of response to the 27-kDa antigen(s) declined to 54% of the 1992 value while responses to a 15/17-kDa antigen(s) remained close to the initial values. Increasing age of the donor predicted higher intensity of antibody to the 15/17-kDa antigen(s) in both the initial (P=0·004) and follow-up (P=0·038) surveys. No relationship was observed between age and antibody intensity for the 27-kDa antigen(s) during either survey (P>0·10). Both the initial and follow-up surveys showed significant elevations in antibody intensity for Talent residents, possibly indicating a high endemic rate of infection/re-infection or high levels of chronic infection.