key: cord-0759228-ho6umj3p
authors: Wee, Liang En; Conceicao, Edwin Philip; Sim, Jean Xiang-Ying; Aung, May Kyawt; Oo, Aung Myat; Yong, Yang; Arora, Shalvi; Ko, Karrie Kwan-Ki; Venkatachalam, Indumathi
title: Sporadic outbreaks of healthcare-associated COVID-19 infection in a highly-vaccinated inpatient population during a community outbreak of the B.1.617.2 variant: the role of enhanced infection-prevention measures
date: 2022-01-30
journal: Am J Infect Control
DOI: 10.1016/j.ajic.2022.01.009
sha: 1f0f2dea42795c1f227eb29e8e76237d7eae38d3
doc_id: 759228
cord_uid: ho6umj3p

Sporadic clusters of healthcare-associated COVID-19 infection occurred in a highly vaccinated HCW and patient population, over a 3-month period during ongoing community transmission of the B.1.617.2 variant. Enhanced infection-prevention measures and robust surveillance systems, including routine-rostered-testing of all inpatients and staff and usage of N95-respirators in all clinical areas, were insufficient in achieving zero healthcare-associated transmission. The unvaccinated and immunocompromised remain at-risk and should be prioritized for enhanced surveillance.

Infection-prevention measures in healthcare settings may mitigate transmission of severe-acute-respiratory-syndrome-coronavirus-2 (SARS-CoV-2), resulting in lower secondary-attack-rates compared to community settings. 1 However, novel variants with higher transmissibility, including the SARS-CoV-2 delta variant (B.1.617.2), challenge containment efforts. Despite usage of appropriate personal-protective-equipment (PPE), healthcareassociated outbreaks of B.1.617.2 have occurred. [2] [3] In Singapore, hospitals instituted extensive infection-prevention measures early-on. [3] [4] However, community outbreaks of B.1.617.2 increased potential spillover into healthcare-facilities. A large nosocomial cluster arising from B.1.617.2 was reported in end-April 2021, 3 providing impetus for routinerostered-testing (RRT) via polymerase-chain-reaction (PCR) testing for inpatients and healthcare-workers (HCWs). 5 We evaluated healthcare-associated transmission of SARS-CoV-2 in a large healthcare-campus during an ongoing community surge of B.1.617.2.

Our healthcare-campus handles COVID-19 and non-COVID-19-admissions, hosting a 1785-bed acute-hospital, a 545-bed community-hospital, and 4 specialist centres. Patients were admitted in cohorted general-wards (5-12 beds/bay, ~1.5 metres apart). Almost 13,000 HCWs work on-campus. The study-period lasted from 27th June 2021-29 th September 2021.

Patients with epidemiological risk (close-contact) were admitted directly to the isolation-ward (negative-pressure isolation-rooms with antechamber), whereas patients without epidemiological risk presenting with clinical-syndromes compatible with COVID-19 were isolated in modified cohort cubicles with reduced bed-density in the "respiratory-surveillance-ward (RSW)" while awaiting PCR. 4 From 27 th June 2021, all inpatient admissions were additionally screened using the BD-Veritor-SARS-CoV-2-antigen rapid-test-kit. 6 Patients with positive antigen-tests were isolated till PCR confirmation.

From April 2021, RRT via PCR-testing of respiratory samples for SARS-CoV-2 was conducted fortnightly for asymptomatic vaccinated HCWs and weekly for non-vaccinated HCWs. 5 Symptomatic HCWs received free testing at our staff clinic. From 19th June 2021, universal inpatient screening was instituted. Asymptomatic patients were tested on admission and weekly subsequently; testing could be performed more frequently at clinician-discretion if patients turned symptomatic. 5

All HCWs in general-ward donned N95-respirators as a mandatory-minimum. HCWs in isolation-ward/RSW donned N95-respirators and disposable gloves, gowns and faceshields. COVID-19 vaccination uptake amongst HCWs was high, with 89.6% fully-vaccinated by end-April 2021. Similarly, 75.0% of inpatients were fully-vaccinated. Pre-pandemic inpatient-areas were cleaned with 1:1000 hypochlorite-based disinfectant 3x-a-day. Regular cleaning and hand-hygiene-compliance were reinforced. 4 UV-C disinfection was also utilized for terminal-cleaning in isolation-areas. All visitors donned masks and if visiting for ≥30 minutes, required antigen-testing. 7 Two asymptomatic, fully-vaccinated visitors/inpatient/day were allowed at maximum. 7 Epidemiological clusters were defined as ≥2 cases in patients or HCWs associated with the same setting, ending when no cases were diagnosed for 14 days. 8 Significant close-contact was defined as contact within 2-metres of the index-case for ≥15 minutes, during the index-case's infectious-period. 8 Infectious periods were defined from 4 days before to 7 days after a positive PCR. 9 Patients and HCWs with significant close-contact underwent PCR on D1/D4/D7/D10 post-exposure, regardless of symptoms. All exposed-patients were isolated; only HCWs who had not donned N95 respirators were furloughed. Whole-genome-sequencing (WGS) was performed for inpatient and HCW-cases in the epidemiological clusters (Supplementary Material 1).

Over a 3-month community surge (Figure 1a ), 6.7% (1219/17676) of admissions had concurrent COVID-19 infection. One-quarter (26.3%, 321/1219) were newly diagnosed during hospitalization (Figure 1b) ; the rest tested positive elsewhere prior. A minority of newly-diagnosed cases (6.9%, 22/321) were healthcare-associated, with the vast majority classified as community-onset (N=299). Antigen-testing combined with epidemiological/clinical risk-stratification was highly successful in triaging suspected community-onset cases to isolation, with a sensitivity of 98.3% (95% CI=96.1-99.5) (Supplementary Table 1 ). Almost all community-onset cases (95.0%, 284/299) were triaged to isolation from onset. Communityonset cases initially triaged outside of the isolation ward (N=15) spent 8.7 hours (S.D=14.6) prior to isolation, seeding two clusters. The first cluster involved an asymptomatic index-case admitted to a cohorted ward with a negative antigen-test/PCR; PCR on D2 of admission returned positive (Figure 2a) . A secondary cluster was seeded on another ward, with sequencing links between patients on both wards (Figure 2a) . The second cluster involved a symptomatic index-case in a cohorted RSW (Figure 2b) .

Amongst healthcare-associated cases (N=22), 7 cases were definite, 12 probable, and the remaining 3 cases indeterminate. The majority (12/22) were unvaccinated; one-third (36.3%, 8/22) received immunosuppression or had malignancy; and one-third (36.3%, 8/22) received hemodialysis. Two-fifths (36.3%, 9/22) were first identified outside of isolation; the remainder were already on enhanced surveillance due to significant inpatient-exposure. Healthcare-associated COVID-19 cases initially detected outside of isolation (N=9) spent 33.3 hours (S.D=22.2) prior to isolation, seeding three clusters. Two clusters comprised definite healthcare-associated inpatient-cases and fully-vaccinated HCWs, with sequencing links (Figure 2c) . A final cluster occurred on a cohorted renal ward (Figure 2d ).

Amongst the five clusters (Figure 2a-d) , 498 HCWs and 107 inpatients had significant close-contact; 1.7% (6/498) of HCWs and 13.1% (14/107) of exposed-inpatients subsequently tested positive. The odds-ratio (OR) of acquisition amongst exposed-inpatients, compared with HCWs, was 12.3 (95% CI=4.6-32.9, p<0.001). One-quarter (23.1%, 6/26) of unvaccinated/partially-vaccinated exposed-inpatients subsequently tested positive, compared with 9.8% (8/81) amongst fully-vaccinated exposed-inpatients (OR= 2.7, 95%CI=0.9-8.8, p=0.08).

Although enhanced infection-prevention measures mitigated potential healthcare-associated transmission of COVID-19, it was insufficient in achieving zero healthcare-associated transmission during widespread community spread. Admission-triage strategies ensured that 95% of community-onset cases were initially isolated, but a single asymptomatic case with negative antigen-testing still resulted in secondary transmission. Enhanced surveillance and rigorous contact-tracing remains crucial in outbreak containment; genomic analysis supplemented epidemiology investigations and facilitated rapid confirmation of clusters, allowing prioritization of infection-prevention resources. The small number of breakthrough infections amongst vaccinated HCWs caring for patients with unsuspected COVID-19 highlights the potential for transmission despite high PPE compliance (≥90%) 10 and widespread usage of N95 respirators. Asymptomatic visitors may escape detection at symptom-based triage and have been implicated in nosocomial clusters; however, screening asymptomatic visitors remains logistically challenging. 7 At our campus, ≥1200 visitors entered daily. No-visitor policies have been considered, but this poses potential psychological distress to patients. The unvaccinated and immunocompromised remain at-risk and should be prioritized for enhanced-surveillance.

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