Table 1 Potential sources and contributing events to transmission of SARS-CoV-2 contributing to the outbreak on the cardiac wards

Lapses in routine practices and additional precautions

Failure to isolate symptomatic patients at symptom onset (10 symptomatic patients in hospital were not isolated for a total of 38 days (range 1–10 days) before outbreak were declared)

Failure to recognize initial cases with illness symptoms compatible with COVID-19 due to crossover with symptoms common to cardiac patients with heart failure (symptomatic patients were not isolated for a total of 15 days (range 1–3) after the outbreaks were declared)

Inappropriate discontinuation of contact/droplet precautions in five patients identified as close contacts of known cases, who initially tested negative (only to test positive later)

Premature (prior to 14-day incubation period) discontinuation of contact/droplet precautions

Suboptimal donning/doffing and hand hygiene by healthcare workers

Uncertainty around performance of a point-of-care risk assessment

Increased patient-to-patient exposures

Shared rooms and bathrooms among 34 (89.5%) patients leading to close contact between patients and potential transmission events through either respiratory droplets/particles across a continuum of sizes and/or contact (direct or indirect)

Transfer of seven patients, identified as close contact to other wards resulting in two forward transmission events

Lapses in environmental cleaning

Potential lapses in environmental cleaning leading to fomite transmission

HCW and visitor exposures

Healthcare worker-related transmission events (e.g., shared breakrooms, carpooling, socializing outside of work) and transmission events related to HCWs interacting with patients between wards up until the outbreak was declared and for several days thereafter before cohorting was strictly enforced

Potential visitor-to-patient transmission with observed visitor non-compliance with masking and distancing recommendations