Heating, ventilation and air conditioning (HVAC) system, microbial air contamination and surgical site infection in hip and knee arthroplasties: the GISIO-SItI Ischia study.

BACKGROUND: Recent studies have questioned the role of unidirectional airflow ventilation system in reducing surgical site infection (SSI) in prosthetic implant surgery. The aim of the ISChIA study ("Infezioni del Sito Chirurgico in Interventi di Artroprotesi" which means "Surgical site infections in arthroplasty surgery") was to evaluate, as a contribution to this debate, the association between heating, ventilation and air conditioning systems, microbial air contamination and surgical site infection in hip and knee arthroplasty.

METHODS: The study was performed from March 2010 to February 2012 in 14 hospitals, for a total of 28 operating theatres: 16 were equipped with vertical unidirectional airflow ventilation (U-OTs), 6 with mixed airflow ventilation (M-OTs), 6 with turbulent airflow ventilation (T-OTs). Microbial air contamination in the operating theatre was evaluated by means of passive (Index of Microbial Air contamination, IMA) and active (Colony Forming Units per cubic metre, cfu/m3) sampling. SSI surveillance was carried out according to the Hospitals in Europe Link for Infection Control through Surveillance protocol.

RESULTS: A total of 1,285 elective prosthesis procedures (61.1% hip and 38.9% knee) were included in the study. The results showed a wide variability of the air microbial contamination in operating theatres equipped with unidirectional airflow. The recommended values of ≤2 IMA and ≤10 cfu/m3 were exceeded, respectively, by 58.9% and 46.4% of samples from U-OTs and by 87.6% and 100% of samples from M-OTs. No significant difference was observed between SSI cumulative incidence in surgical procedures performed in U-OTs compared with those performed in T-OTs. A lower risk of SSI, even though not statistically significant, was shown in surgical procedures performed in U-OTs with a microbial air contamination within the recommended values (≤2 IMA and ≤10 cfu/m3) compared with those performed in U-OTs where these limits were exceeded, and compared with those performed in T-OTs with microbial air contamination within the recommended values for this type of OTs (≤25 IMA, ≤180 cfu/m3.

CONCLUSION: ISChIA study did not show a protective effect of unidirectional airflow compared with turbulent airflow in arthroplasty surgery. However, the frequent exceeding of recommended air microbial contamination values in OTs equipped with unidirectional airflow, and the lower SSI risk in surgical procedures performed in compliant U-OTs compared with those performed in non-compliant U-OTs and with those performed in compliant T-OTs, suggest the need of further studies, which should consider air microbial contamination and other aspects of SSI prevention that may negate the potential benefits of the ventilation system; differences in intrinsic and extrinsic risk factors, medical treatment and surgical technique are also to be considered. Training interventions aimed at improving the behaviour of operators are essential.