Review Airborne Aspergillus fumigatus conidia: a risk factor for aspergillosis C  eline M. O’GORMAN* School of Biology, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom article info Article history: Received 9 June 2011 Received in revised form 11 July 2011 Accepted 11 July 2011 Keywords: Air sampling Aspergillosis Aspergillus fumigatus Composting Fungal spores Outdoor air abstract Aspergillus fumigatus is an opportunistic fungal pathogen that causes invasive aspergillosis, a usually fatal infection. The disease has risen in prominence in recent years due to the increasing numbers of severely immunocompromised patients becoming infected. The fungus is ubiquitous in the environment, producing large numbers of conidia that are dispersed in the air. Humans inhale numerous conidia everyday, but infections are not seen in healthy individuals. As inhalation of conidia is the main route of infection, consid- erable efforts are required to prevent infection in susceptible patients. This review summa- rises the current knowledge on airborne concentrations of A. fumigatus conidia, their background levels in outdoor air and seasonal distribution patterns. New and established methods of air sampling for airborne A. fumigatus conidia are discussed. Common environ- mental sources of the fungus are reviewed, including its presence in compost heaps. Finally, the lack of stringent guidelines on the monitoring and control of airborne A. fumi- gatus concentrations in hospitals is discussed. ª 2011 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. 1. Introduction The filamentous Ascomycete Aspergillus fumigatus is a fungal saprophyte that is ubiquitous throughout the world (Klich, 2002). It typically grows in soil and decaying vegetation such as compost heaps, where it plays an important role in the recycling of carbon and nitrogen (Tekaia and Latg e, 2005). It is also an opportunistic pathogen of immunocom- promised hosts, one of several Aspergillus species that cause a range of allergic, saprophytic, and invasive diseases that are collectively termed ‘aspergillosis’ (Barnes and Marr, 2006; Hope et al., 2008). The most severe form is invasive aspergillosis (IA), and A. fumigatus is responsible for 90 % of cases (Latg e, 2001). Mortality rates of 70e90 % are reported in haematopoietic stem cell transplant recipients, the most at-risk group (Denning, 1998). Despite improve- ments in the diagnosis and treatment of IA, the number of cases and severity of the disease have increased dramati- cally due to the sheer numbers of patients being subjected to increasingly powerful immunosuppressive ther- apies (Barnes and Marr, 2006). For example, Groll et al. (1996) reported a near eight-fold increase in IA cases over a 14-y period from 1978. A. fumigatus is able to reproduce by both sexual and asexual means, producing meiotic ascospores under defined conditions and vast quantities of mitotic conidia on most substrates (Raper and Fennell, 1965; O’Gorman et al., 2009). The asexual conidia extend out in long chains from the vege- tative mycelium, and readily detach to become airborne (Fig. 1). Inhalation is therefore the main route of infection * Tel.: þ44 (0) 115 823 2041; fax: þ44 (0) 115 951 3251. E-mail address: celine.ogorman@nottingham.ac.uk journal homepage: www.elsevier.com/locate/fbr fungal biology reviews 25 (2011) 151 e157 1749-4613/$ e see front matter ª 2011 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.fbr.2011.07.002