Background The Hawthorne effect, or behaviour change due to awareness of being observed, is assumed to inflate hand hygiene compliance rates as measured by direct observation but there are limited data to support this.

Objective To determine whether the presence of hand hygiene auditors was associated with an increase in hand hygiene events as measured by a real-time location system (RTLS).

Methods The RTLS recorded all uses of alcohol-based hand rub and soap for 8 months in two units in an academic acute care hospital. The RTLS also tracked the movement of hospital hand hygiene auditors. Rates of hand hygiene events per dispenser per hour as measured by the RTLS were compared for dispensers within sight of auditors and those not exposed to auditors.

Results The hand hygiene event rate in dispensers visible to auditors (3.75/dispenser/h) was significantly higher than in dispensers not visible to the auditors at the same time (1.48; p=0.001) and in the same dispensers during the week prior (1.07; p<0.001). The rate increased significantly when auditors were present compared with 1–5 min prior to the auditors’ arrival (1.50; p=0.009). There were no significant changes inside patient rooms.

Conclusions Hand hygiene event rates were approximately threefold higher in hallways within eyesight of an auditor compared with when no auditor was visible and the increase occurred after the auditors’ arrival. This is consistent with the existence of a Hawthorne effect localised to areas where the auditor is visible and calls into question the accuracy of publicly reported hospital hand hygiene compliance rates.