BackgroundWe conducted a detailed epidemiological investigation of a linked 2-ward COVID-19 Delta variant outbreak to elucidate its source, risk factors, and control measures.MethodsInvestigations included epidemiologic analysis, detailed case review serial SARS-CoV-2 RT-PCR testing of patients and healthcare workers (HCWs), viral culture, environmental swabbing, HCW-unaware personal protective equipment (PPE) audits, ventilation assessments, and the use of whole genome sequencing (WGS).ResultsThis linked 2-ward outbreak resulted in 17 patient and 12 HCW cases, despite an 83% vaccination rate. In this setting suboptimal adherence and compliance to PPE protocols, suboptimal hand hygiene, multi-bedded rooms, and a contaminated vital signs cart (VSC) with potential fomite or spread via the hands of HCWs were identified as significant risk factors for nosocomial COVID-19 infection.Sudden onset of symptoms, within 72h, was observed in 79% of all Ward 2 patients and 93% of all cases (patients and HCWs) on Ward 2 occurred within one incubation period, consistent with a point source outbreak. RT-PCR assays showed low Cycle threshold (Ct) values, indicating high viral load from environmental swabs including the VSC. WGS results with ≤ 3 SNP differences between specimens were observed.ConclusionsOutbreaks on both wards settled rapidly, within 3 weeks, using a ‘back-to-basics’ approach without extraordinary measures or changes to standard PPE requirements. Strict adherence to recommended PPE, hand hygiene, education, assistance from infected cases (interviews and testing), and additional measures such as limiting movement of patients and staff temporarily were all deemed to have contributed to prompt resolution of the outbreak.