Waterborne outbreak of intestinal microsporidiosis in persons with and without human immunodeficiency virus infection

Among 1454 persons whose stool samples (n = 5692) were submitted to a refer ence laboratory for microsporidia assessment from 1993 to 1996, microsporid ia were identified in 338 persons: 261 persons infected with human immunode ficiency virus (HIV), 16 transplant patients, and 61 others. Intestinal mic rosporidiosis appears to be an endemic disease in HIV-positive persons (pre valence, 0.1%) and a sporadic disease in HIV-negative persons (prevalence, <1/1 million), A waterborne outbreak in 200 persons (attack rate, 1% in HIV -positive patients/month) occurred in the 1995 summer, without evidence of fecal contamination of water. No explanation was found before the outbreak ended, several months before the antiprotease era. Factors associated with microsporidiosis diagnosis were HN infection, male homosexuality, low CD4 c ell counts, and diarrhea, The major factor associated with a diagnosis of m icrosporidiosis during the outbreak was living in an area corresponding to one of the three water distribution subsystems of the town. Lake contaminat ion was suspected.