We report the findings of a longitudinal observational study on HIV-infected patients grouped by presumed transmission group, who had diarrhoea. The purpose of this study was to assess the prevalence of and factors associated with Cryptosporidium infection on these patients. Modified formol-ether concentration followed by modified Ziehl-Neelsen and phenol-auramine/carbol-fuchsin staining techniques were used to identify Cryptosporidium from 465 patients. Cryptosporidiosis was reported in 36/465 (8% and 95% confidence interval 6, 10) patients. Of the positive patients 30 (83%) were men and 6 (17%) women. Prevalence of infection was higher among HIV-seropositive patients whose exposure category was through sexual contact (69%) than among patients in other HIV exposure categories (9%, Standard Z test, P< 0.001). Median CD4+ cell count/mm3 was 120 (range 3-600). Besides diarrhoea, the main clinical manifestations were fever and weight loss in 14 (39%) and 26 (72%) patients, respectively. Cryptosporidium infection was considered to be the first AIDS defining disease in 31% of the patients followed by tuberculosis in 19%, Pneumocystis carinii pneumonia in 14%, Salmonella sepsis in 6%, isosporiasis in 3%, toxoplasmic encephalitis in 3%, leishmaniasis in 3% and Kaposi’s sarcoma in 3% of the patients. There was no significant difference (P= 0.82) in survival times for those given folate antagonists to treat other opportunistic infections. The decrease in prevalence of cryptosporidiosis observed from 1994 until May 1997 is not statistically significant (P= 0.11). Most cases of cryptosporidial infection in AIDS patients in Lisbon occurred in those whose HIV infection was assumed to have been acquired by the sexual route (hetero-, homo-and bisexual), with few cases occurring in drug-abusers.

Cryptosporidium parvum is a pathogenic coccidian parasite with a world-wide distribution. It may produce self-limited diarrhoea in immunocompetent individuals (Ungar et al. 1989, Lengerich et al. 1993, DuPont et al. 1995), but may cause life-threatening disease in patients with AIDS (Current et al. 1983, Malebranche et al. 1983, Ungar 1990, Colford et al. 1996). In healthy adults a low dose of inoculum may be sufficient to cause infection (DuPont et al. 1995). Despite numerous clinical trials with several antimicrobial agents, no therapy has been shown to be curative (Woods et al. 1996, Blagburn and Soave 1997). The infection can be contracted from other humans through sexual contact and nonsexual contact (household contact and nosocomial transmission), through ingestion of contaminated food or drinking water, and contact with infected animals (Current et al. 1983, Ungar 1990, Ravn et al. 1991, Casemore et al. 1994, MacKenzie et al. 1994, Sorvillo et al. 1994, Dworkin et al. 1996). Prevalence reports of cryptosporidiosis in AIDS patients from other workers show rates of 38% in Haiti, 11% in UK, 33% in Italy, 37% in France, 4% in USA (Malebranche et al. 1983, Connolly et al. 1988, Brandonisio et al. 1993, Cotte et al. 1993, Sorvillo et al.