Is Microbiological Sampling of Air in Central Sterile Service Necessary?

Routine measuring air quality by air sampling has been questioned since there is a poor association between air quality and nosocomial infections. In Switzerland, the standard called Good practice for the preparation of sterile medical devices-2005defines air quality standards determined by particle Class 8 (Norm EN ISO 14644-1) in idle state (nobody is in the room) and by microbiological test in operation (upper limit. 200 cfu/m3) to detect malfunction of air conditioning. Dangel and Widmer (2013) sought to investigate qualitatively and quantitatively the microbiological loads before and during work in the CSS of the University Hospital in Basel, Switzerland.

Air sampling was performed with the Microbial Air Sampler MAS-100®. A total of 160 liters of air was aspirated during 95 seconds on Columbia-Agar and Sabouraud plates. Agars were incubated during three days at 35°C followed by 5 percent CO2 for eight days at room temperature. Sabouraud plates were incubated for 21 days to 28°C to identify slow-growing molds. Samples were taken at 6 a.m. (idle), and during the day with maximum occupancy of CSS staff (in operation).

Between July 2008 and February 2013, a total of 209 samples were taken, 116 sample during working hours work and 93 in the absence of any staff. The Swissmedic limit of 200 cfu/m3 was fulfilled in 168 (80.4%) samples, respectively 75 (64.7%) during work and 93 (100%) in an idle state (p<0.001).

Data presented (mean cfu/m3 in idle state vs in work/ p value): Overall (38.9 vs 167.6/0.0001); Coagulase-negative staphylococci (21.5 vs 120.0/0.0001); Corynebacterium (4.0 vs 28.0/0.037); Aspergillus ssp (0.9 vs 2.5/0.030); Staphylococcus aureus (0.0 vs 0.5/0.003); Non-fermenter (0.4 vs 2.6/0.001); Gram-negative bacilli (0.1 vs 2.1/0.001); Other (e.g. Cladosporium ssp, Paecilomyces, Gram-positive Bacilli) (11.8 vs 11.59/0.406).

The researchers concluded that microbiological sampling in CSS during working hours commonly detects pathogenic bacteria and higher counts of molds challenging air conditioners much more than measurements in idle state. They suggest that routine sampling in the idle state should be abandoned; however, the in-operations measurements should be better defined since the number of staff likely influences the results. The researchers say their results indicate that routine measurement in operation should be performed as outlined in the standard.

Reference: Dangel M and Widmer AF. Oral abstract P395 presented at 2nd International Conference on Prevention and Infection Control (ICPIC 2013): The Swiss standard for air quality: does micorobiological air sampling makes sense in central sterilization services (CSS). Antimicrobial Resistance and Infection Control 2013, 2(Suppl 1):P395 doi:10.1186/2047-2994-2-S1-P395.