['Transmission-based precautions (TBPs) are infection control measures designed to interrupt pathogen transmission. Success relies on early recognition of patients with potentially infectious syndromes, then the implementation of appropriate TBPs. We are aware of no literature evaluating interventions to facilitate healthcare workers (HCWs) in implementing TBPs.', "To evaluate the impact of a TBP guidance summary card on HCWs' decision-making about the appropriate implementation of TBPs.", "A prospective audit was carried out to assess HCWs' ability to make decisions about TBP implementation. Following the first audit phase, staff were issued with a guidance card summarizing local TBP guidelines, identifying and addressing relevant TBP measures for infectious syndromes and specific organisms. The audit cycle was then completed to assess the impact of this intervention.", 'Baseline knowledge of appropriate TBP measures was low. Provision of a TBP summary card was significantly associated with the ability of staff carrying the card to correctly decide what TBPs are required in a variety of clinical situations, including Clostridium difficile infection [N = 107; odds ratio (OR): 27.0; 95% confidence interval (CI): 8.37-86.8; P < 0.0001], norovirus diarrhoea and vomiting (N = 107; OR: 94.3, 95% CI: 25.0-356; P < 0.0001), influenza-like illness (N = 107; OR: 85.2; 95% CI: 4.94-1470; P < 0.0001) and the difference between surgical and FFP3 masks (N = 107; OR: 412; 95% CI: 23.4-7246; P < 0.0001).'] Is healthcare workers ' decision-making about transmission-based infection control precautions improved by a guidance summary card?