Trends in Respiratory Virus Infections During the COVID-19 Pandemic in Singapore, 2020

This cross-sectional study assessed the changes in respiratory virus prevalence in 2020 vs 2019 associated with the COVID-19 pandemic.


Introduction
The COVID-19 pandemic brought unprecedented challenges to the world. Many jurisdictions implemented control measures, such as border closures, lockdowns, school and business closures, travel restrictions, mask wearing, and social distancing. This was associated with changes in the prevalence of other respiratory viruses, predominantly influenza viruses 1,2 but others as well. 3 Singapore represents a unique setting that is credited with having a successful COVID-19 response. It went through different response phases, from prelockdown (pandemic level 3) to a full lockdown (known as circuit breaker), followed by a phased reopening, during which schools and businesses reopened but social distancing measures and universal mask wearing remained in place (eTable in the Supplement). Our aim in this study was to assess the associated changes in respiratory virus prevalence in 2020 compared with the prepandemic year 2019.

Methods
In this cross-sectional study, data from respiratory virus multiplex polymerase chain reaction tests from 3 major public hospitals in Singapore for 2019 and 2020 were compiled (eMethods in the Supplement). This included hospital A, a women's and children's hospital (800 beds); hospital B, offering pediatric and adult services (1200 beds); and hospital C, with adult services (1700 beds).
Weekly numbers of tests and positive results for each virus were collated. Institutional review board application and informed consent were not required under SingHealth institutional rules. We followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline. A 1-tailed t test (with significance set at P = .05) was used to compare means.
Data were compiled using Excel 2013 (Microsoft) and analyzed using R version 3.6.2 (R Project for Statistical Computing).

Discussion
COVID-19 pandemic control measures in Singapore were associated with changes across a broad range of respiratory viruses; the changes were most substantial during lockdown. However, the patterns of decrease and subsequent reemergence differed between viruses and pandemic response phases.     For enterovirus/rhinovirus and adenovirus, reductions were only seen after lockdown, and these viruses rebounded earlier than others. Continued mandatory mask wearing did not appear to prevent this. These are small, hydrophilic, nonenveloped viruses that are hardier than others, and we hypothesize that greater relative propensity for contact transmission, in addition to droplet transmission, at a time of increasing social contacts during reopening may have contributed to these findings. 6 The multitude of different enterovirus/rhinovirus and adenovirus types may be another factor contributing to their reemergence.

JAMA Network Open | Infectious Diseases
This study has limitations. The data were obtained from routine diagnostic tests and thus depend on prevailing test requesting patterns. Changes in health care-seeking behavior during the pandemic may have influenced the trends observed.
In conclusion, Singapore's COVID-19 response represents a unique situation of effectively en-