A cluster of invasive aspergillosis in a bone marrow transplant unit related to construction and the utility of air sampling

Background: An investigation was launched to identify the source of a clust er of invasive aspergillosis in the bone marrow transplant unit (BMTU) when construction was taking place on the floor directly below the unit. The ut ility of air sampling for Aspergillus was examined. Methods: Cases of Aspergillus colonization and infection were identified in the BMTU and in the wards adjacent to the construction site. Air sampling was performed in the BMTU before and after room and air duct cleaning and t hen randomly during a 6-month period, beginning 6 months after construction ended. The results were correlated with the incidence of Aspergillus infec tions. Results: The cluster of cases of invasive aspergillosis could not be direct ly linked to the construction, In the BMTU. the rate of Aspergillus coloniz ation and infection during construction was 2.5 times higher than that for the 6 months before the construction and 2.9 times higher for the adjacent wards. After construction ended, the rates returned to preconstruction rate s. Two cases of invasive aspergillosis were observed in the BMTU during ran dom air sampling, but the results of air sampling could not be correlated t o cases. Conclusions: Although the cluster of cases of invasive aspergillosis could not be linked to the construction, the construction did increase the rates of Aspergillus colonization in the BMTU and adjacent wards. Periodic air sa mplings could not correlate conidia counts to invasive Aspergillus infectio n.