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British clinicians who worked in different departments around the hospital were more likely to have been exposed to COVID-19 than those working exclusively on critical care units, a researcher said.

Those who worked in such fields as "diagnostics," (echocardiographers and radiographers), "therapies" (physiotherapists and occupational therapists), and "general" (healthcare assistants and dietitians) were more likely to be SARS-CoV-2 antibody positive than other critical care staff, reported Kate El Bouzidi, MRCP, a PhD candidate at University College London.

Notably, housekeeping staff had the highest prevalence ratio, with all five surveyed staff members seropositive for SARS-CoV-2. All 10 administrators, meanwhile, were seronegative.

The late-breaking study was presented at the Society of Critical Care Medicine's virtual Critical Care Congress, and published in

El Bouzidi said she wanted to determine SARS-CoV-2 seroprevalence in critical care staff, as well as look at the correlation between antibody status, prior swab testing, and COVID-19 symptoms. She added that the critical care department was a good choice for this study, since they had adequate availability of personal protective equipment (PPE) for staff in intensive care units and staff were tested via polymerase chain reaction (PCR) swabs if they became symptomatic.

All staff who worked in the critical care unit in Kings College Hospital in London participated. Serum samples were tested via six different assays to measure receptor-binding domain, nucleoprotein, and tri-spike, with one antibody result determined for each sample.

Overall, of the 625 samples, 21% were positive for SARS-CoV-2 antibodies. During previous PCR testing, about 20% were positive, and all 37 who were PCR-positive were seropositive. However, of the 81 who were PCR-negative, about 19% were now seropositive.

When surveying staff about symptoms, El Bouzidi said researchers were "quite surprised to find 61% of staff reported symptoms they felt could be consistent with COVID-19," with fatigue, headache, and cough as the most common symptoms. Seroprevalence was reported in 31% of symptomatic staff and 5% of asymptomatic staff.

They also found seroprevalence differed by role in a critical care unit, though not significantly by age, sex, ethnicity, or underlying conditions. Consultants were twice as likely to be antibody-positive as junior doctors, for example.

El Bouzidi offered up several hypotheses for these differences, noting that senior doctors "performed more aerosol-generating procedures in the ICU but also maybe in other departments, like the emergency department." They also may have had more household exposure, she said, as those with symptomatic household contacts reported twice the seroprevalence as those without symptomatic household contacts.

She also hypothesized on why staff working in different departments (diagnostics, therapies, and general) were more likely to be seropositive, including different PPE provision around different areas of the hospital, increased mixing with other staff groups and patients, as well as socioeconomic factors.

Researchers examined timing of staff infections, and found they preceded peak of patient admissions by 3 weeks, with peak onset of staff symptoms in early March.

El Bouzidi noted only 10 COVID-19 patients at that point, and "good PPE was available throughout this time."

"Staff were unlikely to be infected by ICU patients, and therefore PPE was largely effective," she added, saying other sources of infection were more likely. Indeed, routine mask wearing was only encouraged in all areas of the hospital as of June 15, 2020.

She concluded that structural approaches to pandemic management were required, such as mitigating risk by staggering breaks and holding virtual meetings and handovers.

El Bouzidi warned that these results may not even apply within Kings College Hospital anymore, since this study was conducted before the more transmissible "U.K. variant" had emerged.

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