Review
Nosocomial aspergillosis in outbreak settings

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Summary

Nosocomial aspergillosis represents a serious threat for severely immunocompromised patients and numerous outbreaks of invasive aspergillosis have been described. This systematic review summarizes characteristics and mortality rates of infected patients, distribution of Aspergillus spp. in clinical specimens, concentrations of aspergillus spores in volumetric air samples, and outbreak sources. A web-based register of nosocomial epidemics (outbreak database), PubMed and reference lists of relevant articles were searched systematically for descriptions of aspergillus outbreaks in hospital settings. Fifty-three studies with a total of 458 patients were included. In 356 patients, the lower respiratory tract was the primary site of aspergillus infection. Species identified most often were Aspergillus fumigatus (154 patients) and Aspergillus flavus (101 patients). Haematological malignancies were the predominant underlying diseases (299 individuals). The overall fatality rate in these 299 patients (57.6%) was significantly greater than that in patients without severe immunodeficiency (39.4% of 38 individuals). Construction or demolition work was often (49.1%) considered to be the probable or possible source of the outbreak. Even concentrations of Aspergillus spp. below 1 colony-forming unit/m3 were sufficient to cause infection in high-risk patients. Virtually all outbreaks of nosocomial aspergillosis are attributed to airborne sources, usually construction. Even small concentrations of spores have been associated with outbreaks, mainly due to A. fumigatus or A. flavus. Patients at risk should not be exposed to aspergilli.

Introduction

Aspergillus spores are ubiquitous in their distribution, and inhalation of spores is believed to be the usual route of transmission. In most healthy individuals, spores are removed by functional innate defence mechanisms such as monocyte-derived and resident macrophages.1 Unfortunately, in severely immunocompromised hosts, such as patients suffering from haematological malignancies2, 3, 4, 5, 6 or solid organ transplant patients,7, 8, 9, 10, 11 invasive aspergillosis (IA) may represent a serious complication in the course of disease. The incidence of IA is increased in these high-risk patients12 with an overall case-fatality rate of one-half to two-thirds.13 IA is difficult to treat and multi-variate analysis has revealed it to be an independent risk factor for mortality in critically ill patients.14

To prevent hospital-acquired aspergillus infections, high-risk patients are usually placed in protective isolation rooms in which positive air pressure is maintained compared with surrounding areas.15 These special rooms are provided with high-efficiency particulate air (HEPA) filters and an air flow of at least 12 air changes/h because HEPA filtration significantly reduces the concentration of fungal spores16 and the incidence of IA.17 In addition, horizontal laminar air flow (LAF) is provided in some facilities which drives contaminants out through the ducts.18 However, additional protection due to LAF remains a matter of debate and the use of LAF is not explicitly recommended by the Centers for Disease Control and Prevention (CDC), the Infectious Disease Society of America (IDSA) or the American Society of Blood and Marrow Transplantation (ASBMT) for the care of haematopoietic stem cell transplant recipients.15, 19 Despite such guidelines for the care of highly susceptible patients and maximum protective efforts, nosocomial outbreaks of IA do occur.19, 20 This systematic review was carried out to summarize the data from all nosocomial aspergillus outbreak reports published to date.

Section snippets

Collection of data

The outbreak database (www.outbreak-database.com), a web-based register of nosocomial epidemics, was searched for outbreaks due to any type of Aspergillus spp.21 Furthermore, a PubMed search (1 January 1966–15 August 2005) was performed to identify additional aspergillus outbreaks by using the term ‘outbreak’ in combination with ‘aspergillus’ or ‘aspergillosis’. References were subsequently screened for additional descriptions of aspergillus epidemics in hospital settings.

Extraction of data

The following data

Results

A total of 53 outbreaks and 458 affected patients were included in this review. Comprising a total of 299 individuals (65.3%), haematological malignancies were the predominant underlying disease. In all but one outbreak, air was the route of fungal spore transmission and the major site of primary infection (356 patients) was the lower respiratory tract.22 Surgical site infections and superficial skin infections were observed far less frequently (24 patients each). Interpatient spread was only

Discussion

Today, construction in or around hospitals is a never-ending phenomenon. This review suggests that construction, renovation, demolition and excavation activities are the main causes of nosocomial aspergillus outbreaks. This is plausible because renovation and demolition work have been shown to increase the amount of airborne fungal spores dramatically,34 and in consequence increase the risk for aspergillus infection in susceptible patients.35 Routes of aspergillus transmission in nosocomial

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