Continuous monitoring of aerial bioburden within intensive care isolation rooms and identification of high-risk activities

Abstract

Background: The spread of pathogens via the airborne route is often underestimated, and little is known about the extent to which airborne microbial contamination levels vary throughout the day and night in hospital facilities.

Aims: To evaluate airborne contamination levels within intensive care unit (ICU) isolation rooms over 10-24-h periods in order to improve understanding of the variability of environmental aerial bioburden, and the extent to which ward activities may contribute.

Methods: Environmental air monitoring was conducted within occupied and vacant inpatient isolation rooms. A sieve impactor sampler was used to collect 500-L air samples every 15 min over 10-h (08:00-18:00 h) and 24-h (08:00-08:00 h) periods. Samples were collected, room activity was logged, and bacterial contamination levels were recorded as colony-forming units (cfu)/m³ air.

Findings: A high degree of variability in levels of airborne contamination was observed across all scenarios in the studied isolation rooms. Air bioburden increased as room occupancy increased, with air contamination levels highest in rooms occupied for the longest time during the study (10 days) (mean 104.4 cfu/m³, range 12-510 cfu/m³). Counts were lowest in unoccupied rooms (mean 20 cfu/m³) and during the night.

Conclusion: Peaks in airborne contamination were directly associated with an increase in activity levels. This study provides the first clear evidence of the extent of variability in microbial airborne levels over 24-h periods in ICU isolation rooms, and found direct correlation between microbial load and ward activity.

Keywords: Air sampling; Airborne; Bacteria; Bioburden; Contamination; Environment.

Figure 1

Statistical control charts (Minitab v17) demonstrating levels of airborne bacteria over a 10-h period (08:00–18:00 h) in patient-occupied isolation rooms within an intensive care unit. Rooms were occupied by patients for differing periods prior to the commencement of air sampling: (a) 8 days, (b) 7 days and (c) 3 days. Each data point represents the probable colony-forming units (cfu)/m³ from air samples taken at 15-min intervals and incubated for 48 h. ‘Out-of-control’ data points are highlighted in red. ‘High-risk’ activities leading to increased airborne bioburden above the mean are identified as follows: a, presence of more than three staff; b, patient personal hygiene/turn; c, bed/sheet changes; d, visiting; e, movement of large equipment into/around room; f, cleaning. UCL, upper control limit; $\overline{\text{X}}$, mean; LCL, lower control limit. N=41.

Figure 2

Statistical control charts (Minitab v17) demonstrating levels of airborne bacteria over a 24-h period (08:00–08:00 h) in occupied and unoccupied inpatient isolation rooms of an intensive care unit. In patient-occupied rooms, rooms were occupied by patients for differing periods prior to the commencement of air sampling: (a) 10 days, (b) 6 days and (c) 1 day. Monitoring of an empty patient room was also included for comparison (d). For analysis, periods of day and night were categorized as 08:00–20:00 h and 20:00–08:00 h, respectively. Each data point represents the probable colony-forming units (cfu)/m³ from air samples taken at 15-min intervals and incubated for 48 h. ‘Out-of-control’ data points are highlighted in red. High-risk activities leading to increased airborne bioburden above the mean are identified as follows: a, presence of more than three staff; b, patient personal hygiene/turn; c, bed/sheet changes; d, visiting; e, movement of large equipment into/around room; f, cleaning. UCL, upper control limit; $\overline{\text{X}}$, mean; LCL, lower control limit. N=97.