In a prospective cohort study of high-risk front-line health care workers (HCWs) in a UK hospital, 44 per cent showed evidence of SARS-CoV-2 infection either by reverse transcription polymerase chain reaction (RT-PCR) or serology, according to results published in The Lancet.
Researchers enrolled 200 patient-facing staff between 26 March 2020 and 8 April 2020 for the SARS-CoV-2 Acquisition in Frontline Healthcare Workers—Evaluation to inform Response study in an acute NHS hospital trust in London.
They collected nasopharyngeal swabs for RT-PCR twice per week, symptom data and blood samples monthly for high-sensitivity serology assays (enzyme-linked immunosorbent assay and flow cytometry for spike glycoprotein).
Total 87 (44%) of the 200 HCWs had evidence of SARS-CoV-2 infection at any time point, detected either by serology or RT-PCR.
Of the 200, 181 gave a valid blood sample at two time points, and 82 (45%) were seropositive after one month: 36/181 (20%) seroconverted during the study and 46/181 (25%) were already seropositive at study entry.
Meanwhile, 42 (21%) of 200 HCWs tested positive for SARS-CoV-2 by RT-PCR in at least one swab. Twenty (48%) reported symptoms within seven days of the positive test, which were consistent with Public Health England's COVID-19 case definition, and 16 (38%) did not report any symptoms in the same time frame.
The median age of study participants was 34 (interquartile range, 29-44) years. There was a trend towards a higher infection rate in participants under 30 years (31 [55%] of 56 positive) compared with those older than 50 years (10 [33%] of 30 positive), with a reduction in log odds of positivity by 0.035 per year (P=.0199).
The mean duration of detection of SARS-CoV-2 RNA by RT-PCR was 12.9 days (first positive to last positive swab; 95% CI, 9.4-17.3). The longest observed duration of SARS-CoV-2 detection was 29 days.
The findings highlight the "urgent need" for better strategies to protect HCWs and patients from nosocomial transmission of COVID-19, the authors said.