Hospital patients were more likely to be infected with Covid-19 by other patients than healthcare workers, research has suggested.
A study by the University of Cambridge found that the vast majority of infections were between patients, and scientists said their work supports that population being tested regularly and wearing masks.
They focused on data between March and June last year, during the UK’s first wave, from five wards at Addenbrooke’s Hospital in Cambridge University Hospitals (CUH) NHS Foundation Trust.
Researchers used statistical methods combining viral genome sequence data with clinical information about people’s locations, which allowed them to identify cases where the data was consistent with transmission occurring between individuals in the hospital.
The study, which is peer-reviewed and is due to be published in the eLife journal on Tuesday, found that out of 22 cases where patients were infected in hospital, 20 were the result of the virus spreading from patients to other patients.
Researchers said their data also suggested that around one fifth of people caused 80% of infection spread.
The paper states: “Based upon dates of individuals reporting symptoms, recorded individual locations, and viral genome sequence data, we show an uneven pattern of transmission between individuals, with patients being much more likely to be infected by other patients than by HCWs (healthcare workers).
“Further, the data were consistent with a pattern of superspreading, whereby 21% of individuals caused 80% of transmission events.”
They said their study “sheds light on the need for intensive and pervasive infection control procedures”.
Dr Estee Torok, senior programme officer in surveillance, data and epidemiology at the University of Cambridge, said: “What we found was that patients were more likely to be infected by other patients than by healthcare workers, and the vast majority of infections occurred in this group.
“Healthcare workers were much less likely to be infected and, if they were, they were equally likely to be infected by other patients or healthcare workers.”
Dr Chris Illingworth, a lead author on the study, who carried out his research while at Cambridge’s MRC Biostatistics Unit, said: “The fact that the vast majority of infections were between patients suggests that measures taken by hospital staff to prevent staff transmitting the virus to patients, such as the wearing of masks, were likely to have been effective.
“But it also highlights why it is important that patients themselves are screened for Covid-19 regularly, even if asymptomatic, and wear face masks where possible.”
Dr William Hamilton, an infectious diseases clinician at the trust and co-lead author on the study, said: “Preventing new cases of hospital-based infection is a critical part of our work.
“Here we have shown that analysing clinical and viral genome sequence data can produce insights that inform infection control measures, which are so important for protecting patients and healthcare workers alike.”
Earlier this month separate research suggested more than one in 10 patients in the UK were infected with Covid-19 during the first wave of the pandemic while being treated in hospital for another reason.
Residential community care hospitals and mental health hospitals were found to have higher levels of hospital-acquired infections, at 61.9% and 67.5% respectively, compared with hospitals providing acute and general care (9.7%) between March and August 2020.
When the research was published rates of hospital-acquired infections had fallen to somewhere between 2% and 5%.