BACKGROUND: Renovation of a general medical ward provided an opportunity to study health care facility design as a factor for preventing hospital-acquired infections.OBJECTIVE: To determine whether a hospital ward designed with predominantly single rooms was associated with lower event rates of hospital-acquired infection and colonization.METHODS: A prospective controlled trial with patient allocation incorporating randomness was designed with outcomes on multiple ‘historic design’ wards (mainly four-bed rooms with shared bathrooms) compared with outcomes on a newly renovated ‘new design’ ward (predominantly single rooms with private bathrooms).RESULTS: Using Poisson regression analysis and adjusting for time at risk, there were no differences (P=0.18) in the primary outcome (2.96 versus 1.85 events/1000 patient-days, respectively). After adjustment for age, sex, Charlson score, admitted from care facility, previous hospitalization within six months, isolation requirement and the duration on antibiotics, the incidence rate ratio was 1.44 (95% CI 0.71 to 2.94) for the new design versus the historic design wards. A restricted analysis on the numbers of events occurring in single-bed versus multibed wings within the new design ward revealed an event incidence density of 1.89 versus 3.47 events/1000 patient-days, respectively (P=0.18), and an incidence rate ratio of 0.54 (95% CI 0.15 to 1.30).CONCLUSIONS: No difference in the incidence density of hospital-acquired infections or colonizations was observed for medical patients admitted to a new design ward versus historic design wards. A restricted analysis of events occurring in single-bed versus multibed wings suggests that ward design warrants further study.