, a new study has found.
“Other staff, other areas of the hospital, and the wider community are more likely sources of infection,” said lead authorSouth London Specialist Virology Centre, King’s College Hospital NHS Foundation Trust, London.
She noted that 60% of critical care staff were symptomatic during the first wave of the coronavirus pandemic and 20% were antibody positive, with 10% asymptomatic. “Staff acquisition peaked 3 weeks before the peak of COVID-19 ICU admission, and personal protective equipment (PPE) was effective at preventing transmission from patients.” Working in other areas of the hospital was associated with higher seroprevalence, Dr. El Bouzidi noted.
The findings were presented at the Critical Care Congress sponsored by the Society of Critical Care Medicine.
The novel coronavirus was spreading around the world, and when it reached northern Italy, medical authorities began to think in terms of how it might overwhelm the health care system in the United Kingdom, explained Dr. El Bouzidi.
“There was a lot of interest at this time about health care workers who were particularly vulnerable and also about the allocation of resources and rationing of care, particularly in intensive care,” she said. “And this only intensified when our prime minister was admitted to intensive care. About this time, antibody testing also became available.”
The goal of their study was to determine the 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.
The survey was conducted at Kings College Hospital in London, which is a tertiary-care teaching center. The critical care department is one of the largest in the United Kingdom. The authors estimate that more than 800 people worked in the critical care units, and between March and April 2020, more than 2,000 patients with COVID-19 were admitted, of whom 180 required care in the ICU.
“There was good PPE available in the ICU units right from the start,” she said, “and staff testing was available.”
All staff working in the critical care department participated in the study, which required serum samples and completion of a questionnaire. The samples were tested via six different assays to measure receptor-binding domain, nucleoprotein, and tri-spike, with one antibody result determined for each sample.
Of the 625 staff members, 384 (61.4%) had previously reported experiencing symptoms and 124 (19.8%) had sent a swab for testing. COVID-19 infection had been confirmed in 37 of those health care workers (29.8%).
Overall, 21% were positive for SARS-CoV-2 antibodies, of whom 9.9% had been asymptomatic.
“We were surprised to find that 61% of staff reported symptoms they felt could be consistent with COVID-19,” she said, noting that fatigue, headache, and cough were the most common symptoms reported. “Seroprevalence was reported in 31% of symptomatic staff and in 5% of those without symptoms.”
Seroprevalence differed by role in a critical care unit, although it did not significantly differ by factors such as age, sex, ethnicity, or underlying conditions. Consultants, who are senior physicians, were twice as likely to test positive, compared with junior doctors. The reason for this finding is not clear, but it may lie in the nature of their work responsibilities, such as performing more aerosol-generating procedures in the ICU or in other departments.
The investigators looked at the timing of infections and found that they preceded peak of patient admissions by 3 weeks, with peak onset of staff symptoms in early March. At this time, Dr. El Bouzidi noted, there were very few patients with COVID-19 in the hospital, and good PPE was available throughout this time period.
“Staff were unlikely to be infected by ICU patients, and therefore PPE was largely effective,” she said. “Other sources of infection were more likely to be the cause, such as interactions with other staff, meetings, or contact in break rooms. Routine mask-wearing throughout the hospital was only encouraged as of June 15.”
There were several limitations to the study, such as the cross-sectional design, reliance on response/recall, the fact that antibody tests are unlikely to detect all previous infections, and no genomic data were available to confirm infections. Even though the study had limitations, Dr. El Bouzidi concluded that ICU staff are unlikely to contract COVID-19 from patients but that other staff, other areas of the hospital, and the wider community are more likely sources of infection.
These findings, she added, demonstrate that PPE was effective at preventing transmission from patients and that protective measures need to be maintained when staff is away from the bedside.
In commenting on the study, Greg S. Martin, MD, professor of medicine in the division of pulmonary, allergy, critical care and sleep medicine, Emory University, Atlanta, noted that, even though the study was conducted almost a year ago, the results are still relevant with regard to the effectiveness of PPE.
“There was a huge amount of uncertainty about PPE – what was most effective, could we reuse it, how to sterilize it, what about surfaces, and so on,” he said. “Even for people who work in ICU and who are familiar with the environment and familiar with the patients, there was 1,000 times more uncertainty about everything they were doing.”
Dr. Martin believes that the situation has improved. “It’s not that we take COVID more lightly, but I think the staff is more comfortable dealing with it,” he said. “They now know what they need to do on an hourly and daily basis to stay safe. The PPE had become second nature to them now, with all the other precautions.”