Ms. Dworkin et al., CRYPTOSPORIDIOSIS IN WASHINGTON-STATE - AN OUTBREAK ASSOCIATED WITH WELL WATER, The Journal of infectious diseases, 174(6), 1996, pp. 1372-1376
In 1994, an outbreak of cryptosporidiosis occurred in a rural communit
y in Washington State where water was supplied by two deep unchlorinat
ed wells. Confirmed case-patients had a stool specimen containing Cryp
tosporidium parvum oocysts. Probable case-patients had diarrhea lastin
g greater than or equal to 5 days. Sixty-two households (68.1% of 91)
responded to a survey, Eighty-six cases (15 confirmed, 71 probable) we
re identified, for an attack rate of 50.9% (86/169 residents). Drinkin
g unboiled well water was associated with being a case-patient (relati
ve risk, 1.84; 95% confidence interval, 0.89-3.82), and a significant
dose-response relationship was found between water consumption and ill
ness (P = .004). Water that was presumed to be treated wastewater from
a piped irrigation system was found dripping along one well's outer c
asing, which was extensively rusted. Presumptive Cryptosporidium oocys
ts were found in well water and in treated wastewater. This investigat
ion demonstrates that even underground water systems are vulnerable to
contamination.