Descriptive analysis of airborne levels of Aspergillus fumigatus present in high-risk critical care patient areas; an eleven-year (2010 – 2021) surveillance study.
Author ORCID Identifier
Date of Award
Master of Public Health (MPH)
Lisa M Casanova, Ph.D.
Scott R. Weaver, Ph.D.
INTRODUCTION: As part of a microbial surveillance effort conducted over an eleven-year period, 38,765 culture samples were collected from various indoor and outdoor spaces within a children’s hospital to determine the baseline levels of a fungus called Aspergillus fumigatus. A. fumigatus is an opportunistic fungus that has proven to be a highly dangerous microorganism; it is ubiquitous in the environment, it is an opportunistic and potent human pathogen and has a high mortality rate in hospitalized immune-compromised patients. In 2014, A. fumigatus was the leading cause of invasive mold infections in the United States in hospitalized patients causing 15,000 cases at the cost of $1.2 billion. Conducting surveillance of this organism in high-risk patient areas, such as intensive care units and operating rooms, is, therefore, a vital component of an effective invasive aspergillosis prevention program.
AIM: The study aimed to determine the level of A. fumigatus present in select areas of a children’s hospital and determine the organism's baseline or “normal” level during periods of no outbreaks. The areas selected to be studied included high-risk areas where patients receive care and treatment and are therefore susceptible to infection; they include: (1) the outdoor environment; (2) intensive care units [ICUs] such as neonatal, cardiac, and pediatric; and (3) operating rooms [ORs], operating theatres or surgical suites. If baseline levels cannot be determined, the results can be compared to published threshold limits to determine if the levels observed in the hospital pose a risk of invasive aspergillosis infection.
METHODS: The hospital provided for evaluation an electronic file consisting of a Microsoft Excel (Excel) spreadsheet containing microbial surveillance data in the form of total viable count (TVC). The TVC data was collected from viable samples obtained throughout the hospital property, explicitly looking for culture results for A. fumigatus. Sample results were reported as Colony Forming Units (CFUs) and collected from outdoor and indoor locations throughout the hospital. The study focused on identifying the locations within the hospital that posed the highest risk of infection by this organism; outdoor, intensive, and critical care areas, and operating room theatres. Next, culture results from each area were segregated using Excel by sorting all samples by location and omitting data if descriptions were incomplete. Finally, a descriptive statistical analysis was performed using the Excel data analysis tool pack to estimate various statistical parameters.
RESULTS: Of the 38,765 culture samples collected, 831 total viable counts (TVC) were positive for A. fumigatus. Of the total positives observed, the outdoor samples comprised 30.3% (252/831), the ICU comprised 9.7% (81/831), and the OR samples comprised 38.9% (323/831). Concerning the number of CFUs per sample, the outdoor sample contained a mean value of 8.3 CFUs, 95% CI (7.90 to 8.75), the ICU samples contained a mean value of 2.4 CFUs, 95% (1.77 to 3.02), and the OR samples contained a mean value of 3.1 CFUs, 95% CI (2.82 to 3.38). The outdoor sample result of 8.3 CFUs had an upper range of 75 CFUs, with a minimum of 1 CFU and a maximum of 76 CFUs. This high variability within the outdoor bioaerosol data is expected and a common observation likely influenced by spatial and temporal variations. The ICU result of 2.4 CFUs and the OR result of 3.1 CFUs contained a far smaller spread, as noted by the range of 30 and 36, respectively. In the case of the ICU and OR, both high-risk areas exceed published threshold limits. The ICU result exceeds the “alert” threshold of 0.5 CFUs and the “action” threshold of 1.0 CFU. The OR result also exceeds the “alert” threshold of 0.1 CFU (with HEPA filtration), 0.6 CFU (without HEPA filtration), and the “action” threshold of 1.0 CFU.
DISCUSSION: Because ICUs and ORs are generally accepted as the clean patient care areas in the hospital, the ICU and OR are expected to contain the lowest concentrations of A. fumigatus. In the case of the OR, it is commonly accepted as the cleanest area of the hospital as it is engineered to be cleaned regularly, typically HEPA filtered, is positively pressurized, contains laminar flow, and undergoes significant air changes per hour. However, microbial surveillance data collected over an eleven (11) year period indicated that culture data within the ICUs and ORs were statistically higher than published threshold limits. When these thresholds are exceeded, the culture data should no longer be characterized as a normal or baseline level since the result is non-compliant and may present a significant risk of invasive aspergillosis. It is not known what the “safe” threshold level of A. fumigatus is, whereby there is no risk of invasive aspergillosis. However, it is clear that the presence of this organism in high-risk areas, such as the ICU and especially the OR, should be prevented and minimized to levels below 0.1 CFU.
Pineda, George H., "Descriptive analysis of airborne levels of Aspergillus fumigatus present in high-risk critical care patient areas; an eleven-year (2010 – 2021) surveillance study.." Thesis, Georgia State University, 2023.
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