Effectiveness of downflow ultraclean air in operating theatres: a correlation study between heating, ventilation and air conditioning (HVAC) systems and surgical site infections

Background: Air quality in operating theatres (OTs) is crucial for preventing surgical site infections (SSIs). HVAC systems should ensure high air quality, minimizing microbial contamination. Recently, the effectiveness of downflow ultraclean air (UCA) systems in preventing SSIs has been debated. Aim: To analyse the correlation between OT HVAC systems and SSI incidence using data from 12 hospitals in the Marche Region (2018–2019). Methods: The data were correlated with the incidence of SSIs following 899 surgical procedures. Logistic regression analysis showed that UCA systems were associated with a reduced risk of SSI (odds ratio: 0.37; 95% confidence interval (CI): 0.15–0.92). Findings: Thirty-eight SSIs were observed, yielding a total incidence of 4.2% (95% CI: 3.0–5.8). Of these, 29 occurred under non-UCA systems (5.17%; 95% CI: 3.5–7.4), and nine occurred in UCA environments (2.66%; 95% CI: 1.2–5.0). Technical data were collected from validation tests in each OT, focusing on UCA HVAC systems with unidirectional airflow meeting ISO 5 class standards. Conclusion: These data suggest the potential effectiveness of UCA in reducing microbial air contamination, thus improving air quality and decreasing the risk of SSIs compared to non-UCA ventilation systems.