High Prevalence of SARS-CoV-2 Antibodies in Care Homes Affected by COVID-19; Prospective Cohort Study, England

Abstract

Background: We investigated six London care homes experiencing a COVID-19 outbreak and found high rates of SARS-CoV-2 infection among residents and staff. Here we report follow-up investigations including antibody testing in the same care homes five weeks later. Methods: Residents and staff in the initial investigation had a repeat nasal swab for SARS-CoV-2 RT-PCR and a blood test for SARS CoV-2 antibodies using ELISA based on SARS-CoV-2 native viral antigens derived from infected cells and virus neutralisation. Findings: Of the 518 residents and staff in the initial investigation, 186/241 (77.2%) surviving residents and 208/ 254 (81.9%) staff underwent serological testing. Almost all SARS-CoV-2 RT-PCR positive residents and staff were seropositive five weeks later, whether symptomatic (residents 35/35, 100%; staff, 22/22, 100%) or asymptomatic (residents 32/33, 97.0%; staff 21/22, 95.5%). Symptomatic but SARS-CoV-2 RT-PCR negative residents and staff also had high seropositivity rates (residents 23/27, 85.2%; staff 18/21, 85.7%), as did asymptomatic RT-PCR negative individuals (residents 61/91, 67.0%; staff 95/143, 66.4%). Neutralising antibody was detected in 118/ 132 (89.4%) seropositive individuals and was not associated with age or symptoms. Ten residents (10/79 retested, 12.7%) remained RT-PCR positive but with higher RT-PCR cycle threshold values; 7/10 had serological testing and all were seropositive. New infections were detected in three residents and one staff. Interpretation: RT-PCR provides a point prevalence of SARS-CoV-2 infection but significantly underestimates total exposure in outbreak settings. In care homes experiencing large COVID-19 outbreaks, most residents and staff had neutralising SARS-CoV-2 antibodies, which was not associated with age or symptoms.

SARS-CoV-2 infection and transmission in educational settings: a prospective, cross-sectional analysis of infection clusters and outbreaks in England

“… 28 Recent serological investigations in care homes have highlighted the extent to which swabbing might underestimate the extent of an outbreak in institutional settings. 29 Moreover, only a few educational settings were selected for wider testing, yet the identification of additional cases suggests that the extent of some outbreaks might have been underestimated. Finally, whole genome sequencing could help to determine whether the outbreaks were caused by a single strain or due to multiple separate introductions and, therefore, not due to transmission within the educational setting.…”

Infection and transmission of SARS-CoV-2 in London care homes reporting no cases or outbreaks of COVID-19: Prospective observational cohort study, England 2020

“…Ongoing investigations in the London care homes offer a unique opportunity to understand factors contributing to the varying outcomes between similar high-risk populations. [ 1 , 18 , 23 ] Follow-up investigations are planned to inform the longevity of antibody responses and the role of cellular immunity, while regular RT-PCR screening will detect SARS-CoV-2 infections and help with our understanding of the risk and frequency of re-infections in care home residents and staff. These data will be critical for informing vaccine strategy in this highly vulnerable group.…”

“…Evidence of virus exposure by either nasal swab SARS-CoV-2 reverse transcription polymerase chain reaction (RT-PCR) positivity or SARS-CoV-2 antibody positivity were compared between these seven ‘non-outbreak’ homes and the initial six outbreak homes. [ 4 , 7 ]…”

Diagnostic tool or screening programme? Asymptomatic testing for SARS-CoV-2 needs clear goals and protocols

“…to diagnose disease), whereas many of those now being tested are asymptomatic. Although a clinically significant proportion of those with infection have no symptoms (with estimates varying from under 50% to around 75%) [ 15 , 20 , 21 ], nevertheless the proportion of the entire asymptomatic general population with infection will be much smaller than the proportion of the symptomatic population with infection. Further, the absence of symptoms suggests different within-host viral dynamics and immune response, meaning it is not possible to extrapolate reliably from a test's performance in symptomatic individuals to ascertain a performance in asymptomatic individuals.…”