Sources and Control of Opportunistic Fungi in The Hospital Environment
By Dr. Harriet Burge, EMLab P&K Chief Aerobiologist and Director of Scientific Advisory Board
Opportunistic fungi attack people with severely compromised immune systems either resulting from medical treatment or disease. Infections with these pathogens are increasing due to the increased use of immunosuppressive medications and diseases such as AIDS that reduce immune competence. Industrial hygienists, hospital infection control personnel, mold investigators and remediators are more and more frequently being called upon to discover the sources of outbreaks of diseases caused by these fungi. Unfortunately, while in other types of environments concentrations of fungi must be relatively high to cause problems, in hospital settings where immunosuppressed patients are housed, airborne concentrations of pathogenic fungi must be maintained at near zero levels. Thus, even very limited growth may be important, and unusual sources must be investigated.
The Fungi Involved
The most common opportunist that is also the most frequent cause of disease is Aspergillus fumigatus, a thermotolerant fungus that not only causes infections, but also colonizes the lungs of asthmatics and people with cystic fibrosis. Other species of Aspergillus that are frequently reported as pathogens are A. terreus, A. niger, and A. flavus. Aspergillus ustus less frequently causes infection (Saracli et al., 2007). Fungi from other genera have also been reported to cause opportunistic disseminated infections, including Scedosporium prolificans (Alvarez et al., 1995), Geotrichum candidum (Scora et al., 2009), Mucor (Sochaj et al., 2009), Pseudallescheria boydii (Thornton 2009), Blastoschizomyces capitatus (Celik et al., 2009), Trichoderma longibrachiatum and closely related Hypocrea orientalis (Druzhinina et al., 2008), and Absidia corymbifera (Parra-Ruiz et al., 2008). Candida albicans, Pneumocystis carinii and other species of Pneumocystis, and Cryptococcus neoformans are also important opportunistic pathogens. Candida is a human commensal that attacks the host when immunosuppression occurs. However, the organism can be transferred between patients and health care workers (Marco et al., 1999). Pneumocystis probably does not grow in the hospital environment, although the fact that it is not culturable may contribute to this perception. It can be readily detected through PCR methods and has been recovered from air (Bartlett et al., 1997). Cryptococcus neoformans is extremely common in the environment, and many people either have or have had subclinical infections. It may become invasive and cause central nervous infections in immunosuppressed patients. This is extremely common in AIDS patients.
The Array of Sources
Person to person transmission. Most fungal opportunists are not transmitted from one person to another. Candida albicans is an exception as is Pneumocystis jerovecii, and probably P. carinii as well. Candida is probably transferred between people by direct contact (Buffington et al., 1994). On the other hand, Pneumocystis is airborne (Yazaki et al., 2009).
Construction. Outbreaks of aspergillosis (invasive Aspergillus infection) related to hospital construction and remodeling have been reported repeatedly (e.g., Alvarez et al., 1995; Ansorg et al., 1996; Lai 2001). As discussed below, outbreaks of infection can be avoided if proper attention is paid to containment during construction activities.
Ventilation Systems. Arnow (1978) was one of the first to note the growth of Aspergillus fumigatus in ventilation systems and the relationship of this growth to aspergillosis. His group conducted environmental monitoring in a new hospital, culturing for Aspergillus and conducting surveillance for aspergillosis cases (Arnow et al., 1991). After airborne concentrations of Aspergillus flavus and A. fumigatus increased to average levels >1 colony forming unit per cubic meter (cfu/m3) and the incidence of aspergillosis increased, filters in the ventilation system were found to be heavily colonized with Aspergillus fumigatus, and A. flavus was found within the hospital rooms. Remediation reduced both airborne concentrations of these fungi and the incidence of aspergillosis. Lutz et al. (2003) reported a similar situation, attributing the contamination to deterioration of insulating material in variable air volume units.
As is the case in all buildings, cellulosic filters that get wet are inevitably colonized with fungi. While Cladosporium is often the dominant type in these situations, Penicillium and Aspergillus species have been recovered as well (Price et al., 2005).
Cleaning Activities. Cleaning activities clearly can raise Aspergillus concentrations in hospitals as well as other sites. In one study, geometric mean concentrations before cleaning were 5.5 cfu/m3 compared to 18.9 one hour after cleaning (P=0.0047) (Lee et al., 2007). In another case, a vacuum cleaner used to clean the floor in a pediatric oncology/hematology ward was found to be the source of Aspergillus fumigatus that led to an outbreak of infection. During vacuum cleaner operation, Aspergillus fumigatus recoveries were 65 cfu/m3 compared to less than 6 cfu/m3 in rooms where this vacuum cleaner was not used (Anderson et al., 1996).
Waste Containers. Hospital waste containers are an obvious potential source for all sorts of infectious agents. Blenkharn (2006) found many organisms including Aspergillus species in these reservoirs.
Plants. Controversy over potted plants as a source for fungal aerosols in hospitals has existed for many years. Thompson et al. (1994) found Aspergillus in 80.5% of his samples of potted plant soil. The most common species were Aspergillus fumigatus and A. niger (Thompson et al., 1994).
Water Systems. Water can contain fungi, and water systems may become colonized. Aspergillus species have been recovered from water taps, patient showers, and ice making machines (Anaissie 2001). Anaissie et al. (2002) found significantly higher concentrations of airborne Aspergillus propagules in bathrooms, where water use was highest (2.95 cfu/m3). In a comparison of different kinds of water sources in hospitals, Kauffmann-Lacroix et al. (2008) found that 52% of the cold water samples contained fungi while only 4% of the hot-water samples had positive cultures. In two hospitals there was generalized growth in the water pipes; one with Exophiala species and the other with Fusarium species. Otherwise, colonization was usually minimal. Nucci et al. (2002) traced the source of infections with Exophiala jeanselmei to deionized water in the hospital pharmacy as well as a water tank and a sink. Genetic comparisons revealed that the cause of the outbreak of infection was the deionized water in the pharmacy. In another interesting study, filamentous fungi were found in more that 94% of all water samples taken in a hospital and all of the samples collected from the intake reservoir. Eighty five percent of the intake reservoir samples contained Aspergillus fumigatus suggesting that this was the source for the fungus in the hospital water. In a second study, this group found that Aspergillus fumigatus strains from air were different genetically from those in water, and that patients had been infected from both sources (Warris et al., 2003).
Matching Sources To Infection Outbreaks
Most of us have our own protocols for building investigations. Hospitals differ primarily in the risk associated with exposure, and the need to document very low concentrations of specific organisms in air. Anderson et al. (1996) describe the steps he took in one investigation where the source turned out to be a vacuum cleaner.
Sampling is most often done using culture (since the organisms must be alive to cause infection). Having found a possible source one can remove or remediate the source, then continue sampling to document that the problem has been solved. However, to be sure that the actual source for the ongoing infections has been identified, it is important to match environmental strains of the fungi to those recovered from the patients. This is done using DNA fingerprinting. Unfortunately, this is more complicated than it appears, at least for Aspergillus fumigatus. It appears that this species is extremely diverse genetically (Symoens et al., 2002). Bart-Delabesse et al. (1999) analyzed 62 environmental isolates to reveal 43 genotypes represented only once. Likewise, isolates from patients were diverse. Chazelet et al. (1998) fingerprinted more than 700 clinical and environmental isolates of Aspergillus fumigatus and found that 85% of the isolates recovered from air represented different strains. To qualify as nosocomial (hospital acquired) patients must be infected with an isolate found in the environment, or multiple patients at the same site must be infected with the same genotype (Bart-Delabesse et al., 1999; Chazelet et al., 1998). Chazelet et al. (1998) considers that the frequent lack of common strains among patients involved in an outbreak is due to the extreme genetic diversity of Aspergillus fumigatus. It is also true that the same strain can appear throughout a hospital, and can persist for many months (Girardin et al., 1994) and that the same patient can be infected with more than one strain (Menotti et al., 2005).
Aspergillus flavus is less common than A. fumigatus, and infections in patients appear to be more likely to match environmental isolates. Ao et al. (2007) matched two patient isolates to two environmental strains of Aspergillus flavus. Three other patients had strains that differed from those in the environment, but two of these patients had the same strain. Thus, four out of five of these patients were assumed to have nosocomially acquired infections. In another Aspergillus flavus case, Buffington et al. (1994) found environmental strains in a patient and a health care worker, but different strains in two other patients. Heinemann et al. (2004) investigated an outbreak of surgical site infections with Aspergillus flavus. He found a single clone of the organism throughout the surgical suite and in the patients. On the other hand, Leenders et al. (1996) found distinctly different strains of Aspergillus flavus in a group of patients arguing against a hospital source for the infections.
Outbreaks related to Aspergillus terreus have also been investigated. Lass-Flori et al. (2000) was able to match Aspergillus terreus strains from potted plant soil to infections in four patients.
Some people strongly recommend monitoring of the hospital environment in order to detect the beginning of an episode of contamination. The problem is, how often and how extensive should monitoring protocols be? Alberti et al. (2001) recommend monitoring for changes in the entire fungal population (not just Aspergillus species) as this indicates the potential for conditions that could lead to growth of opportunists. Falvey & Streifel (2007) found spikes of Aspergillus associated with infection during a monitoring period and considered this data useful in the search for sources. Monitoring protocols should include notation of activities going on before or during the monitoring period. Some transient activities as well as conditions that become chronic clearly affect aerosolization of fungi and the presence of these conditions and activities help to focus on the source of spikes. On the other hand, monitoring may reveal spikes not related to any apparent activity and may indicate the need for more extensive investigations.
Prevention of hospital contamination and patient infection is a multifaceted task. The outdoor air must be filtered, the systems supplying outdoor air to the hospital environment must be maintained so that they are water free, activities within the hospital that raise dust must be minimized or isolated, and patients may have to be protected directly through medications and/or masking. All of these precautions apply especially to immunocompromised patients.
HEPA filtration of the outdoor air is almost universally recommended (Araujo 2008; Benet et al., 2007; Brenier-Pinchart et al., 2009; Falvey & Streifel 2007). Comparing outdoor air, HEPA-filtered air and other hospital locations, Falvey & Streifel (2007) found Aspergillus species in 95% of outdoor air samples, 33% of HEPA-filtered locations, and 50% of other hospital areas.
Laminar air flow is also sometimes used to protect immunocompromised patients, but it involves high air exchange rates, is expensive, and causes noise and drafts (Humpfreys 2004).
Air purifiers and mobile units have been marketed to protect immunosuppressed patients either routinely or under especially hazardous conditions. Poirot et al. (2007) tested a mobile unit that provided an environment with no detectable airborne fungi regardless of levels outside of the unit's influence. Bergeron et al. (2007) tested a mobile nonthermal plasma air treatment unit that significantly reduced airborne spore concentrations. However, portable air filtration units were not capable of significantly reducing air concentrations in rooms (Englehart et al., 2003). Of course the amount of air processed per unit time and the amount of disturbance of dust during unit operation would contribute to these results. On the other hand, compliance was poor due to noise and thermal discomfort.
Protection from activities within the hospital that may produce fungal aerosols is extremely important. Many hospitals have installed anterooms next to rooms housing at-risk patients in part so that gowning and hand washing activities can take place outside of the patient's environment (Araujo 2008; Brenier-Pinchart et al., 2009). Activity with rooms without anterooms and other restrictions on aerosol production led to a direct correlation between activity and fungal spore levels. On the other hand, aerosols in rooms with control measures were related to outdoor concentrations, emphasizing the need for high quality filtration.
One activity in hospitals that is well known to produce fungal aerosols is construction. Many approaches have been used to prevent construction-related outbreaks of aspergillosis in hospitals. Most follow the same principles of containment that should be used for all occupied spaces. Given the greatly enhanced susceptibility of immunosuppressed patients, additional efforts may need to be made. Cornet et al. (1999) used laminar flow and HEPA filtration in rooms adjacent to the construction and no Aspergillus was found in any subsequent air sample in these protected spaces. In addition to HEPA filtration, Loo et al. (1996) used biocide containing paint and non-perforated ceiling tiles, sealed all windows, replaced horizontal blinds with roller shades, and called for systematic and regular cleaning of surfaces. With these efforts he was able to reduce the incidence of aspergillosis to levels below pre-construction levels, and far below those that had pertained during the initial phase of construction. Use of water to reduce airborne dust concentrations in construction areas has been used, but the risk of mold growth resulting from damp conditions must be considered (Berthelot et al., 2006). Daily particle count measurements in high risk areas can encourage compliance with infection control measures during construction (Prezant et al., 2005).
Finally, one can act directly at the patient level to prevent infection. Removing patients from high risk areas and the use of well fitted masks are two approaches that are commonly used (Maschmeyer et al., 2009; Chang et al., 2008; Berthelot et al., 2006; Raad et al., 2002). In addition, some physicians use prophylactic anti-fungal agents in their patients to reduce the risk of fungal infections (Chang et al., 2008).
There are currently no specific guidelines for acceptable concentrations of any individual opportunistic fungus in hospitals. It appears that any guideline would have to be in a range less than 1 cfu/m3 to be effective for immunocompromised patients. Alberti et al. (2001) reviewed the literature on "safe" levels of Aspergillus. He found opinions on decreased levels that ranged from 0.009 - <0.2 cfu/m3 (total Aspergillus spores). On the other hand, risk appears to start increasing near 1 cfu/m3.
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This article was originally published on January 2010.