Correspondence on "The Low Yield of SARS-CoV-2 Rapid Antigen Testing in Screening Asymptomatic Hospital Visitors in Low-incidence Settings".

To the Editor,

We note the interest by Boddeti et al. (Boddeti et al., 2022) in our article that reported the use of rapid-antigen detection (RAD) in screening asymptomatic hospital visitors for SARS-CoV-2 at the point-of-entry during the COVID-19 pandemic (Wee et al., 2022).

During the study period 0.3% (31/9679) of admitted inpatients tested positive for COVID-19. In contrast, retrospective contact tracing together with RAD testing for visitors staying ≥30 minutes identified COVID-19 cases among <0.01% (6/72605) of hospital visitors. In June 2021, Singapore was at Level 1 of the US Centers for Disease Control and Prevention (CDC)’s Travel Health Notice Thresholds (CDC, 2020), with an incidence of <50 cases of COVID-19 over the past 28 days per 100,000 population. Singapore raised to Level 3 only at the end of September 2021 (100-500 cases over the past 28 days per 100,000 population). As of June 2021, 58.1% of the local population had received a single vaccine dose, with 36.8% of the population having had 2 doses (MOH, 2021). Only visitors who intended to visit for ≥30 minutes received RAD testing. A single test result was taken as valid for the purposes of entry triage for 24 hours; whereas frequent visitors would have had serial daily testing, it was infeasible to require 2 separate negative tests 24-48 hours apart for a single hospital visit. As previously cited, the use of the national digital contact-tracing tool to register entry/exit to hospital premises was made compulsory for all visitors who had to pass through mandatory perimeter screening regardless of visit duration (Wee et al., 2021), allowing retrospective contact tracing of potential exposures arising from all visitors who subsequently tested positive for COVID-19 elsewhere. Although most visitors (82.4%, 10521/12763) remaining on hospital premises for ≥30 minutes did undergo RAD testing, a small minority of them were not tested because they overstayed beyond the initial visit duration that was declared. Only visitors with recent previous polymerase chain reaction (PCR)-confirmed COVID-19 infection received an exemption from RAD testing. No CONSORT (Consolidated Standards of Reporting Trials) flow diagram was included as this was an observational study.

During the study period, a total of 6 visitors with PCR-confirmed COVID-19 infection were thus identified, and the epidemiological details are given in Table 1 of the study. Identifying information for visitors was omitted as most of them were not patients at our hospital, and this was not relevant for contact-tracing investigations. For the single case of PCR-confirmed COVID-19 infection picked up on RAD screening (Case 6), RAD tests on preceding visits were negative.

Funding source

This research was not grant funded.

Ethics approval

Because this study was conducted as part of an outbreak investigation, ethics approval was not required under our institutional review board guidelines.

Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.