Elucidating the origins of nosocomial infections with Candida albicans by DNA fingerprinting with the complex probe Ca3

Computer-assisted DNA fingerprinting with the complex probe Ca3 has been us ed to analyze the relatedness of isolates collected from individuals with n osocomial bloodstream infections (BSIs) and hospital care workers (HCWs) in the surgical and neonatal intensive care units (ICUs) of four hospitals. T he results demonstrate that for the majority of patients (90%), isolates co llected from commensal sites before and after collection of a BSI isolate w ere highly similar or identical to the BSI isolate. In addition, the averag e similarity coefficient for BSI isolates was similar to that for unrelated control isolates. However, the cluster characteristics of BSI isolates in dendrograms generated for each hospital compared to those of unrelated cont rol isolates in a dendrogram demonstrated a higher degree of clustering of the former. In addition, a higher degree of clustering was observed in mixe d dendrograms for HCV isolates and BSI isolates for each of the four test h ospitals. In most cases, HCW isolates from an ICU were collected after the related BSI isolate, but in a few cases, the reverse was true. Although the results demonstrate that single, dominant endemic strains are not responsi ble for nosocomial BSIs in neonatal ICUs and surgical ICUs, they suggest th at multiple endemic strains may be responsible for a significant number of cases. The results also suggest that cross-contamination occurs between pat ients and HCWs and between HCWs in the same ICU and in different ICUs. The temporal sequence of isolation also suggests that in the majority of cases HCWs are contaminated by isolates from colonized patients, but in a signifi cant minority, the reverse is true. The results of this study provide the f ramework for a strategy for more definitive testing of the origins of Candi da albicans strains responsible for nosocomial infections.