Influence of the operating theatre ventilation system on prosthetic joint infections: the ISChIA study of the Italian Group of Study GISIO – SItI

Background The role of unidirectional air flow (UAF) in preventing surgical site infections (SSI) following interventions of hip replacements has been challenged by recent studies showing no benefit and even greater risk. These studies did not evaluate the air microbiological quality of operating theatres (OT) presuming its coherence with the characteristic of the Heating, Ventilation and Air Conditioning (HVAC) system. Aim(s)/Objective(s) The multicentre ISChIA (Infezioni del Sito Chirurgico in Interventi di Artroprotesi) study funded by the Italian Ministry of Health was aimed at evaluating the association between HVAC used in OTs, microbial air contamination and risk of SSI in hip and knee prosthesis in order to give a contribution to the debate about the protecting role of UAF. • Method Microbial air contamination was evaluated in the patient area of OT, once when empty and during each operation by passive (Index of Microbial Air contamination, IMA) and active sampling (colony forming unit, cfu/m3). SSI surveillance was conducted according to the HELICS protocol (2004). • Results 1,232 interventions were included, 60.2% of hip and 39.8% of knee replacements. In 42.9% an UAF was available. Microbial contamination was shown to increase significantly during the interventions; in more than half air samplings collected in UAF-OT, microbial contamination was higher than the recommended levels. IMA values positively correlated with the number of persons and the number of door openings. No association was shown between risk of SSI and the characteristic of the HVAC, even though a lower risk of SSI was observed in operations performed in OTs with the microbial air quality consistent with the UAF, although not significantly. • Discussion, and/or Conclusion Our study failed in showing any protective role of UAF on SSI. However, despite the high costs of UAF system the levels of air contamination were often higher than expected; therefore, an evaluation of the UAF technology cannot be performed without an appraisal of the level of air contamination levels.