Investigating the variability of airborne bacteria in a hospital Intensive Care Unit over a 24 hour period

Current knowledge of the clinical microflora is limited, however it is currently estimated that 10-33% of nosocomial infections are transmitted via air. This study aims to assess the variability and dynamics of airborne contamination in a hospital setting, and contribute to an improved understanding of the airborne bioburden in clinical environments.
Environmental air monitoring, using a sieve-impactor air sampler, was conducted in an Intensive Care Unit, with 500L air samples collected every 15-min over 24-h periods (08:00-08:00h). Room activity was logged and bacterial contamination levels were recorded as CFU/m3 of air. A cascade impactor and aerosol spectrometer were also used to separate particles into size fractions correlating to human lung deposition.
A high degree of variability in airborne contamination was observed over the course of a 24-h period in the hospital ICU. Contamination counts ranged from 12-510 CFU/m3 over 24-h in an isolation room occupied for 10 days by a patient with C. difficile infection. Levels were lowest during the night and in unoccupied rooms, with an average value of 20 CFU/m3. Peaks in airborne contamination showed a direct relation to an increase in room activity, such as bed changes and visiting times.

This study demonstrates the variation and degree of airborne contamination that can occur in an ICU over a 24-h period. Numerous factors contributed to increasing microbial air contamination and consideration should be given to potential improved infection control strategies and decontamination technologies to reduce airborne contamination, with the ultimate aim of reducing healthcare-associated infections from environmental sources.