SIR—In the 1 November 2001 issue of Clinical Infectious Diseases, Anaissie and Costa [1] presented their hypothesis that implicated hospital water as a major source of filamentous fungi. More recently, Dr. Anaissie and other colleagues reported the results of a study that showed an association of fusariosis with pathogenic Fusarium species recovered from a hospital water distribution system [2]. We agree with the authors of these 2 studies that there has been an increase in data that support hospital water as a potential source of filamentous fungi and, in particular, Aspergillus fumigatus, as well as preliminary data that support the possibility of waterborne transmission of these molds. Still, the origin of filamentous fungi that contaminate hospital water has yet to be resolved. We have previously shown that 94% of water samples obtained from inside the National Hospital (Oslo, Norway) harbored filamentous fungi. Of the variety of molds recovered from tap water samples obtained from the pediatric bone marrow transplantation unit of this hospital, A. fumigatus accounted for 35% of the total number of colony-forming units [3]. During a recent survey performed in the hematology ward of the University Medical Center Nijmegen (Nijmegen, The Netherlands), we cultured Fusarium species from several environmental samples obtained by swabs from showerhead surfaces, but we were unable to culture any molds, including A. fumigatus, from hospital water samples, itself. We assumed that the kind of natural reservoir that serves as the water source for hospital water systems determines the level of contamination of hospital water with molds. In Norway, the population and industry within the city of Oslo are supplied drinking water for which surface water is the origin. This water undergoes only a simple treatment process that involves aeration, microstraining, and chlorination. In contrast, in Nijmegen, The Netherlands, ground water is the origin of the water supply for drinkable water, including the water supply for the hospital. Rainwater diffuses through layers of sand that serve as a natural filter. The ground water is pumped to the surface from a great depth and has a temperature of ∼4°C. This water undergoes no further treatment other than correction of the pH. After the water is pumped to the surface, it is stored in large closed tanks. Water samples that were obtained from each of the water sources, both before and after the purification procedure was performed, showed a remarkable difference in the recovery of molds, including A. fumigatus (for the recovery methods used, see [3]). No molds were recovered from samples obtained from ground water, whereas 100% of the samples taken from surface water yielded molds. Furthermore, 55% of the surface water samples yielded A. fumigatus. In Oslo, the number of colony-forming units cultured from the water samples was not affected by the purification process. These results strongly suggest that the type of water source has a significant impact on the recovery of molds from hospital water. If water is stored in a manner that allows it to have contact with ambient air (e.g., storage in a surface water reservoir), fungal contamination will occur, and a diversity of molds can be recovered from outlets (e.g., taps, showers) inside the hospital. On the contrary, in “closed water supply systems” (e.g., storage of ground water in reservoirs where contact with ambient air is prevented), fungal contamination appears to be insignificant. Furthermore, our results suggest that current water purification procedures, such as chlorination, do not eliminate fungal spores. Another remarkable observation involves the disparity noted in the recovery of A. fumigatus in our studies, compared with the recovery reported by Anaissie et al. [2]. In their study, only 1% of the samples taken from water and waterrelated surfaces inside the hospital yielded A. fumigatus [4], whereas our study showed that A. fumigatus was present in 40% of all water samples obtained from inside the hospital in Oslo [3]. Indeed, the natural reservoir may be responsible for this enormous disparity in recovery of A. fumigatus.
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Warris et al. (2002) studied this question.