A practical approach to investigating nosocomial acquisition of Aspergillus

Invasive mould disease (IMD) has a high mortality in immunosuppressed patients. Invasive aspergillosis (IA) is the most common IMD. A guideline for preventing IA has been published jointly by the Centers for Disease Control and Prevention, the Infectious Disease Society of America, and the American Society of Blood and Marrow Transplantation. Use of high-efficiency particulate air filters, adequate air exchange rates, sealing of patient rooms, and preventing exposure to moulds by nursing patients in areas away from construction sites are recommended by the guideline. However, there is limited information in relation to the actions to be undertaken by infection prevention and control teams in the event of one or more cases of nosocomial aspergillosis. In this review, we describe a systematic approach to aspergillosis by defining possible and probable nosocomial acquisition based on the number of days since hospital admission. We advocate an incremental response to the investigation of nosocomial aspergillosis in patients in protective isolation taking into account the number of cases and the likelihood of nosocomial origin. For single cases of nosocomial IA, we suggest that infection control investigations should focus on case surveillance and walk-through inspection escalating in a stepwise manner to enhanced case surveillance, verification of environmental controls, environmental monitoring, genotyping of clinical and environmental isolates, and review of antifungal prophylaxis for multiple cases and outbreaks. Where applicable, the construction site should be inspected with the aim to reduce the dispersal of conidia. Surveillance systems need to be strengthened to better understand the epidemiology of IA.