This study attempted firstly to correlate environmental contamination of air and surfaces in the intensive care unit (ICU); and secondly, to examine any association between environmental contamination and ICU-acquired staphylococcal infection.
We screened patients, air and surfaces on 10 sampling days in a mechanically ventilated 10-bed ICU during 10 months.
Near-patient hand-touch sites (n=500) and air (n=80) were screened for total colony count and Staphylococcus aureus using dipslides, settle plates (passive air sampling) and an MAS-100 slit-sampler (active air sampling). Air counts were compared with surface counts according to proposed standards for air and surface bioburden. Patients were monitored for ICU-acquired staphylococcal infection throughout.
Overall, 235 of 500 (47%) surfaces failed the standard for aerobic counts (≤2.5 cfu/cm2). Half of passive air samples (20 of 40: 50%) failed the ‘Index of Microbial Air’ contamination (2 cfu/9cm plate/hr), and 15/40 (37.5%) active air samples failed the clean air standard (<10 cfu/m3). Settle plate data was closer to the pass/fail proportion from surfaces and also provided the best agreement between air parameters and surfaces when evaluating surface benchmark values between 0-20 cfu/cm2. The surface standard most likely to reflect hygiene pass/fail results compared with air was 5 cfu/cm2. Rates of ICU-acquired staphylococcal infection were associated with surface counts/bed during 72 hours encompassing sampling days (p=0.012).
Passive air sampling provides quantitative data analogous to that obtained from surfaces. Settle plates could serve as a proxy for routine environmental screening to determine the infection risk in ICU.