Density and molecular epidemiology of Aspergillus in air and relationship to outbreaks of Aspergillus infection

After five patients were diagnosed with nosocomial invasive aspergillosis c aused by Aspergillus fumigatus and A. flavus, a 14-month surveillance progr am for pathogenic and nonpathogenic fungal conidia in the air within and ou tside the University Hospital in Rotterdam (The Netherlands) was begun. A. fumigatus isolates obtained from the Department of Hematology were studied for genetic relatedness by randomly amplified polymorphic DNA (RAPD) analys is. This was repeated with A. fumigatus isolates contaminating culture medi a in the microbiology laboratory. The density of the conidia of nonpathogen ic fungi in the outside air showed a seasonal variation: higher densities w ere measured during the summer, while lower densities were determined durin g the fall and winter. Hardly any variation was found in the numbers of Asp ergillus conidia, We found decreasing numbers of conidia when comparing air from outside the hospital to that inside the hospital and when comparing o pen areas within the hospital to the closed department of hematology. The i ncrease in the number of patients with invasive aspergillosis could not be explained by an increase in the number of Aspergillus conidia in the outsid e air. The short-term presence of A. flavus can only be explained by the pr esence of a point source, which was probably patient related. Genotyping A. fumigatus isolates from the department of hematology showed that clonally related isolates were persistently present for more than 1 year. Clinical i solates of A. fumigatas obtained during the outbreak period were different from these persistent clones. A. fumigatas isolates contaminating culture m edia were all genotypically identical, indicating a causative point source, Knowledge of the epidemiology of Aspergillus species is necessary for the development of strategies to prevent invasive aspergillosis. RAPD fingerpri nting of Aspergillus isolates can help to determine the cause of an outbrea k of invasive aspergillosis.