BackgroundWe conducted a prospective study to investigate the presence of microfungal contamination in the water supply system of the Oncology Paediatric Institute, São Paulo – Brazil after the occurrence of one invasive Fusarium solani infection in a patient after Haematopoietic Stem Cell Transplantation (HSCT). During a twelve-month period, we investigated the water supply system of the HSCT unit by monitoring a total of fourteen different collection sites.MethodsOne litre of water was collected in each location, filtered through a 0.45 μm membrane and cultured on SDA to detect the presence of filamentous fungi. Physicochemical analyses of samples were performed to evaluate the temperature, turbidity, pH, and the concentration of free residual chlorine.ResultsOver the 12 months of the study, 164 samples were collected from the water supply system of the HSCT unit, and 139 of the samples tested positive for filamentous fungi (84.8%), generating a total of 2,362 colonies. Cladosporium spp., Penicillium spp., Purpureocillium spp. and Aspergillus spp. were ranked as the most commonly found genera of mould in the collected samples. Of note, Fusarium solani complex isolates were obtained from 14 out of the 106 samples that were collected from tap water (mean of 20 CFU/L). There was a positive correlation between the total number of fungal CFU obtained in all cultures and both water turbidity and temperature parameters. Our findings emphasise the need for the establishment of strict measures to limit the exposure of high-risk patients to waterborne fungal propagules.ConclusionsWe were able to isolate a wide variety of filamentous fungi from the water of the HSCT unit where several immunocompromised patients are assisted.