A pilot study to evaluate the airborne bacterial load in veterinary surgical theatres without controlled ventilation systems

Abstract

With an estimated 98% of the bacterial load in a clean surgical incision being derived from airborne pathogens, the bioaerosol composition of the theatre environment plays a determining role in the development of surgical site infections. From literature, focusing on human surgical theatres, it has been demonstrated that the concentration of viable airborne bacteria is influenced by the level of room occupancy, utilization of appropriate surgical attire and proper ventilation systems. Only limited information is however available for the veterinary profession. This pilot study was aimed at evaluating the airborne bacterial load in veterinary practices which did not have the financial means for surgical theatre ventilation systems. Antimicrobial testing was furthermore performed to evaluate overall resistance of circulating bacteria in theatres. Four veterinary facilities were recruited into the study. The sites differed in their surgical attire requirements, staff present during procedures and total daily throughput. As a way of quantifying the organisms that could settle in an incision, blood agar settle plates were placed within one meter of the incision site, from first incision to last suture, for routine canine or feline sterilizations. A total of 45 settle plates were collected and subjected to manual bacterial colony forming unit counts. Species were identified using the Sensititre ARIS 2x automated system; while antimicrobial susceptibility testing followed standard CLSI methodology. After a total sampling time of 843 minutes, 487 bacterial isolates from 53 species were identified. Micrococcus (28.8%) and Staphylococcus (16.8%) represented nearly half of the isolates. A further 61.8% (24 species) could be classified as human and/or small animal commensals, with all but 4 being Gram-positive. Ten of the 53 isolated species (37.2% of isolates) were previously implicated in small animal surgical site infections (SSI’s). Sensitivity testing was possible for 20.9% of the isolates representing 77.4% of the identified species. Resistance was detected in 58.8% of samples (80.5% of species). Of the organisms previously implicated in SSI’s, 7 were tested for their antimicrobial susceptibility. Micrococcus isolates were resistant to kanamycin (7.1%), cephalothin (14.3%) and sulfisoxazole (28.6%). Trimethoprim/sulpha (20.0%) and erythromycin (20%) resistance was detected in Staphylococcus pseudintermedius whilst S. aureus was susceptible to all antimicrobials. The single coagulase-negative Staphylococcus isolate was resistant to enrofloxacin, the Pseudomonas organism to cephalothin and Enterococcus to kanamycin, enrofloxacin, sulfisoxazole and tetracycline. Resistance to all 6 antimicrobials were detected in the single Enterobacter isolate. Due to the limited sample size and variables between the facilities, it was not possible to make a statistically supported conclusion. Specific trends were however evident. A high level of room occupancy, lack of appropriate surgical attire, in conjunction with exposure to the outside environment, were factors associated with the high bacterial count. A correlation between the total occupancy time and commensal load was evident, with the higher throughput facilities yielding more commensal organisms per time period sampled, likely as a result of organism accumulation during consecutive procedures. For these reasons, it is concluded that current infection mitigation practices were not ideal to minimize the SSI risk. The routine wearing of correct attire and the implementation of routine cleaning procedures to reduce the bioburden for patient benefit are recommended.