Hospital staff may be carrying SARS-CoV-2, the coronavirus that causes COVID-19 disease, without realising they are infected, according to a study by researchers at the University of Cambridge.
Patients admitted to National Health Service (NHS) hospitals are now routinely screened for the SARS-CoV-2 virus, and isolated if necessary. But NHS workers, including patient-facing staff on the front line, such as doctors, nurses and physiotherapists, are tested and excluded from work only if they develop symptoms of the illness. Many of them, however, may show no symptoms at all even if infected, as a study demonstrates.
The Cambridge team pro-actively swabbed and tested over 1,200 NHS staff at Addenbrookes Hospital, Cambridge University Hospitals NHS Foundation Trust, throughout April. The samples were analysed using a technique called PCR to copy and read the genetic information of material present on the swab, producing a colour change whenever the coronavirus was present in a specimen. At the same time, staff members were asked about relevant coronavirus symptoms.
Of the more than 1,000 staff members reporting fit for duty during the study period, 3% nevertheless tested positive for the coronavirus. On closer questioning, around one in five reported no symptoms, two in five had very mild symptoms that they had dismissed as inconsequential, and a further two in five reported COVID-19 symptoms that had stopped more than a week previously.
To probe routes of possible transmission of the virus through the hospital and among staff, the researchers also looked at whether rates of infection were greater among staff working in “red” areas of the hospital, those areas caring for COVID-19 patients. Despite wearing appropriate personal protective equipment (PPE), “red” area staff were three times more likely to tested positive than staff working in COVID-19 free “green” areas.
It’s not clear whether this genuinely reflects greater rates of transmission from patients to staff in red areas. Staff may have instead transmitted the virus to each other or acquired it at home. Staff working in the “red” areas were also swabbed earlier in the study, closer to when the lockdown was first initiated, so the higher rates of infection in this group might just be a symptom of higher rates of virus circulating in the community at the time.
Nevertheless, extrapolating these results to the more than half a million patient-facing staff working across the NHS UK-wide suggests that as many as 15,000 workers may have been on duty and infected, with the potential to transmit the virus to co-workers, family members and patients, during the month of April. In fact, this figure could be even higher in settings where the supply of PPE has been very problematic.
The implications of the new study, say senior authors Dr Mike Weekes and Professor Stephen Baker from the Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID), are that hospitals need to be vigilant and introduce screening programmes across their workforces.
“Test! Test! Test! And then test some more,” Weekes explains. “All staff need to get tested regularly for COVID-19, regardless of whether they have any sort of symptoms – this will be vital to stop infection spreading within the hospital setting.”
The research was mainly funded by Wellcome and the Addenbrooke’s Charitable Trust.
Significant differences exist in the availability of healthcare worker (HCW) SARS-CoV-2 testing between countries, and existing programmes focus on screening symptomatic rather than asymptomatic staff. Over a 3-week period (April 2020), 1,032 asymptomatic HCWs were screened for SARS-CoV-2 in a large UK teaching hospital. Symptomatic staff and symptomatic household contacts were additionally tested. Real-time RT-PCR was used to detect viral RNA from a throat+nose self-swab. 3% of HCWs in the asymptomatic screening group tested positive for SARS-CoV-2. 17/30 (57%) were truly asymptomatic/pauci-symptomatic. 12/30 (40%) had experienced symptoms compatible with coronavirus disease 2019 (COVID-19) >7 days prior to testing, most self-isolating, returning well. Clusters of HCW infection were discovered on two independent wards. Viral genome sequencing showed that the majority of HCWs had the dominant lineage B∙1. Our data demonstrates the utility of comprehensive screening of HCWs with minimal or no symptoms. This approach will be critical for protecting patients and hospital staff.
Lucy Rivett, Sushmita Sridhar, Dominic Sparkes, Matthew Routledge, Nick K Jones, Sally Forrest, Jamie Young, Joana Pereira-Dias, William L Hamilton, Mark Ferris, M Estee Torok, Luke Meredith, Martin D Curran, Stewart Fuller, Afzal Chaudhry, Ashley Shaw, Richard J Samworth, John R Bradley, Gordon Dougan, Kenneth G C Smith, Paul J Lehner, Nicholas J Matheson, Giles Wright, Ian G Goodfellow, Stephen Baker, Michael P Weekes
The Guardian reports, meanwhile, that NHS bosses have told senior doctors and nurses that up to a fifth of patients with COVID-19 in several hospitals contracted the disease over the course of the pandemic while already being treated there for another illness. Some of the infections were passed on by hospital staff who were unaware they had the virus and were displaying no symptoms, while patients with coronavirus were responsible for the others.
The figures represent NHS England’s first estimate of the size of the problem of hospital-acquired COVID-19, which Boris Johnson last week said was causing an “epidemic” of deaths.
In a national briefing last month on infection control and COVID-19, NHS England told the medical directors and chief nurses of all acute hospitals in England that it had found that 10%-20% of people in hospital with the disease had got it while they were inpatients.
Senior doctors and hospital managers say that doctors, nurses and other staff have inadvertently passed on the virus to patients because they did not have adequate personal protective equipment (PPE) or could not get tested for the virus.
According to the report, doctors say that hospital-acquired COVID-19 is a significant problem and that patients have died after becoming infected that way. NHS chiefs remain concerned about the extent of a problem doctors call nosocomial infection.Cambridge University material eLie abstract Full report in The Guardian