Clustering of giardiosis among AIDS patients in Los Angeles County

The purpose of this study was to determine the mode of the spread of the enteric parasitic infections among HIV+/AIDS patients attending the AIDS clinic of the King/Drew Medical Center in Los Angeles. Two hundred forty three patients diagnosed with HIV+/AIDS agreed to participate. The study was conducted by several interviews, questionnaires and stool sample collections over a one year period. Stool samples were processed for protozoan cysts and Helminth Ova using standard stool concentration and staining techniques. An indirect immunofluorescence monoclonal antibody technique was also used as an alternate to detect the parasites in samples. Forty three cases were positive for Giardia Lamblia (17.7%) and 10 cases were positive for Cryptosporidium (4%). No Helminth Ova were detected. The majority of the participants were African-American (72.6%) and 27.6% were Hispanic. Clustering studies were performed to determine the mechanism of spread of the parasites among the population study. The Nearest Neighbor Clustering Technique (NNT) was used to determine if there was spatial clustering of positive cases. Geocoding with the MapInfo Program was performed to determine the precise coordinates of the residence of the subjects. Application of the NNT showed a high degree of clustering for Giardia. The NNT statistic for Giardia was significant with the p value for 0.020 using the Simes multiple comparisons correction. Examination of the map plots indicated that there were two areas with high Giardia prevalence, one in Hollywood region, the other in South-Central Los Angeles. The odds ratio for sexual orientation was 14.2 (for homosexuals vs heterosexuals) with a p value of less than 0.001. These findings strongly suggest that male homosexual contact was the main mode of transmission of observed Giardia cases.