Evaluation of the airborne contamination levels in an intensive care unit over a 24 hour period

L. Dougall, E. Khoo, H. Hood, M. MacLean, M. G. Booth, S.J. MacGregor

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Airborne transmission of infectious microorganisms poses a critical threat to human health, particularly in the clinical setting where it is estimated that 10-33% of nosocomial infections are spread via the air. Within the clinical environment, microorganisms originating from the human respiratory tract or skin can become airborne by coughing and sneezing, and periods of increased activity such as bed and dressing changes, movement, staff rounds and visiting hours. Current knowledge of the clinical airborne microflora is limited and there is uncertainty surrounding the contribution of airborne microorganisms to the transmission of nosocomial infection. This study aims to establish an improved understanding of the variability in the dynamics and levels of airborne microbial contamination within an operational intensive care unit (ICU).

Environmental monitoring of airborne contamination levels was conducted in Glasgow Royal Infirmary ICU, in the open ward and in both occupied and unoccupied patient isolation rooms. Monitoring was performed using a sieve impactor air sampler, with 500 L air samples collected every 15 minutes over 10 hour (08:00-18:00 h) and 24 hour (08:00-08:00 h) periods. Samples were collected on tryptone soya agar (TSA) plates, and the bacterial contamination levels were recorded as CFU/m3 of air. An activity log was also collated over the 10 hour and 24 hour sampling periods in order to record any activity occurring in the ward/room that might contribute to spikes in airborne contamination levels.

Results highlight the degree of variability in levels of airborne contamination over the course of both a working day and a 24 hour period in a hospital ICU. A high degree of variability was observed across the 24 hour period, with counts ranging from 12-510 CFU/m3 in one study in an occupied patient room. Peaks in airborne contamination showed a direct relation to an increase in room activity. Monitoring found contamination levels to be lower overall during the night, and in unoccupied isolation rooms, with an average value of 20 CFU/m3. The highest counts were observed in an isolation room occupied for 10 days by a patient with C. difficile infection which generated an average microbial load of 104 CFU/m3 and a peak value of 510 CFU/m3.

This study has demonstrated the degree of airborne contamination that can occur in the ICU environment over a 24 hour period. Numerous factors were found to contribute to the microbial air contamination levels, including patient status, length of room occupation, time of day and room activity, and further work is required to establish the extent to which this airborne bioburden contributes to cross-infection of patients.
Original languageEnglish
Number of pages1
Publication statusPublished - 25 Jan 2018
Event 27th Scottish Intensive Care Society Annual Scientific Meeting - Fairmont Hotel, St Andrews , United Kingdom
Duration: 25 Jan 201826 Jan 2018


Conference 27th Scottish Intensive Care Society Annual Scientific Meeting
Country/TerritoryUnited Kingdom
CitySt Andrews


  • airborne contamination
  • ICU
  • intensive care units
  • microbial contamination
  • air study


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