Cross Sectional investigation of a COVID-19 outbreak at a London Army barracks: neutralising antibodies and virus isolation

Taylor, Hannah; Wall, William; Ross, David; Janarthanan, Roshni; Wang, Liyang; Aiano, Felicity; Ellis, Joanna; Gopal, Robin; Andrews, Nick; Patel, Monika; Lackenby, Angela; Myers, Richard; Ramsay, Mary E; Chow, J. Yimmy; Zambon, Maria; Ladhani, Shamez N

Background Military personnel in enclosed societies are at increased risk of respiratory infections. We investigated an outbreak of Coronavirus Disease 2019 in a London Army barracks early in the pandemic. Methods Army personnel, their families and civilians had nasal and throat swabs for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) by reverse transcriptase -polymerase chain reaction, virus isolation and whole genome sequencing, along with blood samples for SARS-CoV-2 antibodies. All tests were repeated 36 days later. Findings During the first visit, 304 (254 army personnel, 10 family members, 36 civilians, 4 not stated) participated and 24/304 (8%) were SARS-CoV-2 RT-PCR positive. Infectious virus was isolated from 7/24 (29%). Of the 285 who provided a blood sample, 7% (19/285) were antibody positive and 63% (12/19) had neutralising antibodies. Twenty-two (22/34, 64%) individuals with laboratory-confirmed infection were asymptomatic. Nine SARS-CoV-2 RT-PCR positive participants were also antibody positive but those who had neutralising antibodies did not have infectious virus. At the second visit, no new infections were detected, and 13% (25/193) were seropositive, including 52% (13/25) with neutralising antibodies. Risk factors for SARS-CoV-2 antibody positivity included contact with a confirmed case (RR 25.2; 95%CI 14-45), being female (RR 2.5; 95%CI 1.0-6.0) and two-person shared bathroom (RR 2.6; 95%CI 1.1-6.4). Interpretation We identified high rates of asymptomatic SARS-CoV-2 infection. Public Health control measures can mitigate spread but virus re-introduction from asymptomatic individuals remains a risk. Most seropositive individuals had neutralising antibodies and infectious virus was not recovered from anyone with neutralising antibodies. Funding PHE