The risk of Covid-19 infection among staff at the height of the coronavirus pandemic was lowest among intensive care clinicians, contrary to expectations, according to findings in one UK hospital.
In contrast, coronavirus risk was found to be highest among acute and general medicine clinicians, staff from Black, Asian and minority ethnic (BAME) backgrounds, and cleaners.
“All these factors are important for considering what’s going to happen this winter”
Researchers suggested the type of personal protective equipment (PPE) worn may be key to the differences and was, therefore, likely to be relevant for any second surge or seasonal flu this winter.
The findings, published in the journal Thorax, are based on a study at University Hospitals Birmingham NHS Foundation Trust, one of the largest acute trusts in the UK with over 20,000 staff.
Five patients with serious Covid-19 infection were being admitted every hour at the height of the pandemic, according to the study authors from University of Birmingham College of Medical and Dental Sciences.
They noted that, at the time, there was no national NHS staff testing capacity, so no way of knowing who was infected and at risk of passing it on to patients, or who had already had the infection.
For the study, staff with no Covid-19 symptoms were offered a test for both current and previous infection – using throat and nose swabs to detect antigen, and a blood test to detect antibodies.
All the staff were at work over the course of 24 hours between 24 and 25 April 2020, around a month after the UK went into lock down.
They were asked to report any illnesses consistent with Covid-19 that they had had in the previous four months. Information on ethnicity and department of work was also collected.
Nearly 2.5% of the 545 staff with no symptoms at the time tested positive, of which 38% subsequently developed symptoms.
Around 26% of the 516 for whom serum samples were available said they had previously had symptoms consistent with Covid-19.
Staff with previous symptoms were significantly more likely to have antibodies than those who had not had symptoms – 37% versus 17% – and they had higher levels of antibodies.
The overall prevalence of antibody positivity among the participants was 24%, compared with 6% generally in the Midlands at the time.
When the researchers looked at the figures by staff area, they said striking differences in antibody positivity emerged.
Cleaners had the highest seroprevalence (34.5%), followed by clinicians working in acute medicine (33%) or general internal medicine (30%).
The lowest seroprevalence was found among staff working in intensive care medicine (15%), emergency medicine (13%), and general surgery (13%).
There was also an ethnic divide, as has previously been highlighted by earlier studies and evidence, prompting significant concerns around equality.
According to the Birmingham study, staff from BAME backgrounds were nearly twice as likely to have already had the infection as their White colleagues.
Lead study author Professor Alex Richter said: “We presumed intensive care workers would be at highest risk. But workers in ITU are relatively well protected compared with other areas.”
The researchers suggested the reasons underlying the findings were likely to be “multi-factorial”.
“In accordance with national guidelines, intensive care units were designated high-risk environments and the use of enhanced PPE including filtered face piece (class 3) respirators mandated.
“In contrast, fluid-resistant surgical masks were recommended in other clinical areas,” noted the researchers.
Professor Richter added: “All these factors are important for considering what’s going to happen this winter.
“Cases [of coronavirus] are on the rise. Are we going to have another surge? If there is one, how do we protect healthcare workers this winter?” she said in a podcast on the study.
“And let’s think not just about SARS-CoV-2 and the lessons we can learn for other pandemics, but seasonal infection,” she said. “Influenza has a massive impact on the NHS every winter.”