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Prevention of nosocomial aspergillosis
1Department of Medicine, School of Public Health, University of Minnesota, Minneapolis 55455.
Abstract:
Unfiltered outside air averages 1-15 pathogenic Aspergillus sp. colony forming units (cfu) m-3 although short-term fluctuations are substantial. Seasonal variation reflects increased spore prevalence during periods of greater availability of non-viable matter. In hospital, airborne spores reflect incomplete filtration, infiltration of outside air and shedding of adherent spores from introduced objects. In highly protected hospital areas supplied with air filtered at high efficiency, where aspergillus cfus may be as low as 0.01 cfu m-3, infiltration and shedding contribute a high fraction of ambient spores. Nosocomial aspergillosis occurs in linear proportion to the mean ambient hospital airborne spore content. An analysis presuming a steady-state dynamic equilibrium is imperfect because repeated sampling produces occasional high counts which violate a Poisson distribution. 'Mini-bursts' arise from disturbance of settled spores in dust, shedding spores from clothes or other subtle sources. These sources are best mitigated by increasing the air change rate. It is most important to protect bone marrow transplant patients, leukaemia and lymphoma patients undergoing intensive, potentially curative therapy. The optimal protective environments include high filtration efficiency, point-of-use filters, protection against infiltration and filter bypass, elimination of in-hospital sources, and high air change rates.
Insights
Hospital airborne Aspergillus spores, measured in colony forming units (cfu) per cubic meter, correlate with nosocomial aspergillosis risk. High air change rates and filtration are crucial for protecting vulnerable patients.
Area of Science:
- Environmental microbiology
- Hospital infection control
- Medical mycology
Background:
- Airborne Aspergillus spores are prevalent outdoors and indoors, posing a risk in healthcare settings.
- Hospital airborne spore levels are influenced by outdoor air, filtration efficiency, and internal sources.
- Nosocomial aspergillosis incidence correlates with ambient airborne Aspergillus spore concentrations.
Purpose of the Study:
- To analyze airborne Aspergillus spore dynamics in hospital environments.
- To identify sources and contributing factors to airborne Aspergillus in hospitals.
- To inform strategies for preventing nosocomial aspergillosis.
Main Methods:
- Air sampling to quantify Aspergillus colony forming units (cfus) per cubic meter.
- Analysis of spore prevalence, seasonal variations, and hospital-specific factors.
- Evaluation of environmental controls and their impact on spore levels.
Main Results:
- Outdoor air contains 1-15 Aspergillus sp. cfus m-3, with seasonal variations.
- In hospitals, infiltration and shedding contribute significantly to airborne spores, even with high-efficiency filtration.
- Occasional high spore counts ('mini-bursts') violate steady-state models and are linked to dust disturbance and shedding.
Conclusions:
- Airborne Aspergillus spore levels are a critical factor in nosocomial aspergillosis.
- Increasing air change rates effectively mitigates 'mini-bursts' from subtle sources.
- Optimal protection for immunocompromised patients requires high-efficiency filtration, infiltration control, and high air change rates.