title: How clean must our drinking water be: the importance of protective immunity.
abstract: BACKGROUND
  Cryptosporidium parvum is an important cause of epidemic diarrhea. Few studies have assessed whether serological evidence of prior infection in adults is related to a reduced occurrence of enteric illness.
  
  
  METHODS
  Serum samples and enteric illness event data were obtained in 2000 and 2001 from 326 people served by 1 of 2 unfiltered surface sources or 1 groundwater source. In 2001, filtration was initiated at 1 of the surface sources. Poisson regression related illness episodes with serological responses to the 15/17- and 27-kDa Cryptosporidium antigen groups.
  
  
  RESULTS
  Subjects with moderately strong responses to the 15/17-kDa antigen had <65% of the risk of all 1-3-day episodes of diarrheal or gastrointestinal illness and <40% of the risk of all >/=4-day episodes, compared with subjects without a moderately strong response. Water source, change in water treatment, and very weak responses were unrelated to illness events.
  
  
  CONCLUSIONS
  Endemic Cryptosporidium infections are a common cause of diarrheal and gastrointestinal illness in persons without a moderately strong response to the 15/17-kDa antigen group. Users of surface-derived drinking water are more likely to have strong serological responses to this antigen group and may be at a lower risk of endemic gastrointestinal illness caused by Cryptosporidium infection.
authors.affiliation: Lovelace Clinic Foundation, The Lovelace Respiratory Research Institutes, Albuquerque, New Mexico, USA.
authors.forename: Floyd J
authors.initials: FJ
authors.lastname: Frost
authors.forename: Melissa
authors.initials: M
authors.lastname: Roberts
authors.forename: Twila R
authors.initials: TR
authors.lastname: Kunde
authors.forename: Gunther
authors.initials: G
authors.lastname: Craun
authors.forename: Kristine
authors.initials: K
authors.lastname: Tollestrup
authors.forename: Lucy
authors.initials: L
authors.lastname: Harter
authors.forename: Tim
authors.initials: T
authors.lastname: Muller
mesh_terms: D000328:Adult; D000368:Aged; D000913:Antibodies, Protozoan / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D003457:Cryptosporidiosis / Q000453:epidemiology* / Q000276:immunology*; D003967:Diarrhea / Q000453:epidemiology / Q000276:immunology; D005260:Female; D005767:Gastrointestinal Diseases / Q000453:epidemiology / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate; D008297:Male; D016012:Poisson Distribution; D011446:Prospective Studies; D014867:Water / Q000469:parasitology*; D014881:Water Supply / Q000592:standards
chemical_list: D000913:Antibodies, Protozoan; D014867:Water