Air sampling methods to evaluate microbial contamination in operating theatres: results of a comparative study in an orthopaedics department

https://doi.org/10.1016/j.jhin.2011.10.011Get rights and content

Summary

Aim

To evaluate the level of microbial contamination of air in operating theatres using active [i.e. surface air system (SAS)] and passive [i.e. index of microbial air contamination (IMA) and nitrocellulose membranes positioned near the wound] sampling systems.

Methods

Sampling was performed between January 2010 and January 2011 in the operating theatre of the orthopaedics department in a university hospital in Southern Italy.

Findings

During surgery, the mean bacterial loads recorded were 2232.9 colony-forming units (cfu)/m2/h with the IMA method, 123.2 cfu/m3 with the SAS method and 2768.2 cfu/m2/h with the nitrocellulose membranes. Correlation was found between the results of the three methods. Staphylococcus aureus was detected in 12 of 60 operations (20%) with the membranes, five (8.3%) operations with the SAS method, and three operations (5%) with the IMA method.

Conclusion

Use of nitrocellulose membranes placed near a wound is a valid method for measuring the microbial contamination of air. This method was more sensitive than the IMA method and was not subject to any calibration bias, unlike active air monitoring systems.

Introduction

Air biocontamination and related health effects are an emerging public health problem. Airborne bacteria, fungi and viruses can cause infection in diverse living or working environments. This is particularly relevant in medical facilities where there are susceptible patients and tissues are exposed to the air during surgery. As such, there is a need for various systems to minimize the introduction, generation and retention of particles in these environments.1, 2 In this context, microbiological monitoring of air quality is useful in order to determine the potential exposure of individuals at risk.

The control of air biocontamination was first deemed to be necessary in order to reduce the risk of deep wound infections in prodedures such as hip arthroplasties.3, 4 It is generally accepted that bacterial contamination of the air in operating theatres, predominantly caused by contaminated skin scales shed from the surgical team, is the main factor causing surgical site infection after clean operations.1, 5, 6

Whilst the procedures for microbiological assessment of other environmental matrices are established in European Law (e.g. methods are specified for the identification of microbes from water samples), there are no established regulations for air monitoring other than the international norm ISO 14698. This states that different sampling methods exist and different types of devices are commercially available, each with limitations, thus leaving the choice of system open.7, 8 Microbiological content of the air can be monitored by two principal methods: active and passive monitoring of air flows.8 In active monitoring, a microbiological air sampler physically draws a known volume of air through or over a particle collection device, which can be liquid or solid, and the number of micro-organisms present is given in colony-forming units (cfu)/m3 of air. This system is applicable when the concentration of micro-organisms is not very high, such as in an operating theatre.2, 9, 10 Passive monitoring uses ‘settle plates’ (i.e standard Petri dishes containing culture media) that are exposed to the air for a given time to collect biological particles; these ‘sediment’ out and are subsequently incubated. Results are expressed in cfu/plate/time or cfu/m2/h.11

Several studies have compared the two sampling methods with discordant results; some studies have found significant correlation between the methods,11, 12, 13, 14 while other studies have found no correlation.15, 16 In particular, Friberg et al. proposed an equation that permits the transformation of the number of cfus settling on a plate over 1 h (cfu/plate/h) into air contamination units (cfu/m3).11, 17

One of the most important questions that still needs to be resolved is whether the data from these monitoring systems are actually relevant to what is happening on the operating table. If one of the principal causes of air biocontamination is the surgical team, the results from the general room monitoring systems may underestimate the real risk of exposure to the patient on the surgical table, which may be surrounded by air with a higher level of micro-organisms.

To evaluate this hypothesis, the present study investigated and compared the levels of air contamination measured with active and passive systems, and also evaluated the level of air contamination near the wound using nitrocellulose membranes.18, 19

Section snippets

Methods

This study was undertaken between January 2010 and January 2011 in the operating theatre of the Department of Orthopaedics and Traumatology of the University Hospital ‘Policlinico Consorziale’, Bari, Italy. Microbial sampling was undertaken during 60 total hip arthroplasties, all performed in the same operating theatre (dimensions 8.7 m × 4.3 m, height 3.14 m, total volume 117.467 m3). The operating theatre is equipped with a turbulent ventilation system of four low-level inlets with air forced

Results

The mean bacterial load for the IMA samplings was 2232.9 (SD 859.7) cfu/m2/h (range 786–4246), which was significantly lower than the results obtained with the nitrocellulose membranes [mean 2768.2 (SD 1325.4) cfu/m2/h, range 1153–6344; t = −2.62, P = 0.0049]. A mean value of 123.2 (SD 58.7) cfu/m3 (range 40–288) was measured with the SAS sampler.

A significant correlation was found between the IMA values and the SAS values (r2 = 0.73, P < 0.0001, Figure 2), and both of these were significantly

Discussion

Infections can be debilitating complications of primary hip arthroplasty, and have been cited as the most common cause of implantation failure.23 Many contributing factors have been implicated such as patient factors, surgical technique and postoperative factors,24 but the environment, progress of the operation, clothes worn, etc. are also important. In this context, the microbiological quality of the air in operating theatres is a significant parameter to control surgical infection, and

Conflict of interest statement

None declared.

Funding sources

University of Bari financial support for scientific research.

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