First nosocomial cluster of COVID-19 due to the Delta variant in a major acute care hospital in Singapore: investigations and outbreak response

Abstract

Objectives The first large nosocomial cluster of COVID-19 in Singapore in April 2021 led to partial closure of a major acute-care hospital. We report our investigations and evaluate the effectiveness of the BNT162.b2 and mRNA1273 vaccines against the Delta variant. Methods Close contacts of COVID-19 patients and the affected ward were identified and underwent surveillance for SARS-CoV-2 infection. Patient, staff and visitor cohorts were constructed and factors associated with infection evaluated. Phylogenetic analysis of patient samples was performed. Ward air exhaust filters were tested for SARS-CoV-2 virus. Results There were 47 cases in total, comprising 29 patients, 9 staff, 6 ward visitors and 3 household contacts. All infections were of the Delta variant. Ventilation studies showed turbulent airflow and swabs from air exhaust filters were positive for SARS-Cov2. Vaccine breakthrough infections were seen in both patients and staff. Among patients, vaccination was associated with a 79% lower odds of infection with COVID-19 (adjusted OR =0.21, 95%CI 0.05-0.95) Conclusions This cluster occurred despite an enhancement in infection control measures that the hospital had undertaken at the onset of this pandemic, but it was rapidly brought under control through case isolation, extensive contact tracing and quarantine measures, and led to enhancements in hospital personal protective equipment (PPE) use, introduction of routine rostered testing of inpatients and staff, and hospital infrastructure changes to improve ventilation within the general ward.

Nosocomial Outbreak by Delta Variant From a Fully Vaccinated Patient

“…Although vaccination is a critical tool for reducing transmission, other preventive strategies and infection control measures are still needed, as suggested by previous reports of nosocomial outbreaks during the delta era. 8 9 Testing of the index was performed 2 days after symptom onset; thus diagnosis and isolation were delayed. Previously, we found that the infectors who transmit the virus tended to have a longer duration from symptom onset to isolation than the non-infectors ( P = 0.083).…”

Prevention of SARS-CoV-2 and respiratory viral infections in healthcare settings: current and emerging concepts

“…Current hospital architectural standards stipulate a minimum of 6 air changes per hour in clinical spaces, more in procedural and operative areas. This is considerably more air changes compared to the estimates associated with well-documented superspreading events in hospitals, nursing homes, hospices, restaurants, and churches [14,15,61–65]. Higher air changes are associated with less recovery of SARS-CoV-2 from the air in hospitalized patients’ rooms, faster clearance of respiratory aerosols, and less viral exposure for healthcare personnel [66 ▪▪ ,67,68].…”

Genomic epidemiology of Delta SARS-CoV-2 during transition from elimination to suppression in Aotearoa New Zealand

“…The astonishing speed at which Delta spread led to outbreaks in many countries that had previously achieved elimination. For example, Delta outbreaks in Australia, Fiji, Vietnam, Singapore and Taiwan demonstrated how previous public health measures used to control COVID-19 were less effective against this highly transmissible variant [5][6][7][8][9] .…”