FOUR in 10 healthcare workers who test positive for Covid show no symptoms of the disease, raising fears over "silent transmission" of the virus in settings such as hospitals and care homes.

Researchers called for precautionary screening of all healthcare workers exposed to the virus, regardless of symptoms, adding that the evidence underlined the importance of quality personal protective equipment (PPE) for staff.

The findings are based on an analysis of 97 existing studies, up to July 8, covering more than 230,000 healthcare workers in 24 countries.

The study found that 10 per cent of healthcare workers had tested positive for the virus using the PCR antigen test, which detects a current or recent infection, while a further 7% tested positive for SARS-CoV-2 antibodies - indicating that they had been infected in the past.

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Of those who known to have had Covid, nearly half (48%) were nurses, followed by physicians (25%) and other healthcare workers.

Pooled data from 15 studies showed that 40% of those healthcare workers who had tested positive on the PCR test were not displaying any symptoms of infection - such as loss of taste or smell, fever, muscle pain, or a persistent cough - at the time of diagnosis.

Oscar H Franco, co-author of the study and professor of epidemiology and public health at the University of Bern's Institute of Social and Preventive Medicine (ISPM) in Switzerland, said: "Health care workers are the frontline response to Covid-19, exposing themselves to a higher risk of acquiring the disease, and subsequently, exposing patients and colleagues."

He added that the findings highlighted the need for universal testing.

Prof Franco said: "Because we might miss a large proportion of Covid-19 cases if screening targets only symptomatic healthcare workers, universal screening for all exposed healthcare workers regardless of symptoms should be the standard strategy.

"While more research is needed to understand specific interventions that can help reducing SARS-CoV-2 infection among healthcare personnel, it is clear that providing healthcare workers with adequate personal protective equipment and training is essential."

Co-author and colleague at the ISPM, Dr Taulant Muka, added: "A significant proportion of healthcare workers are positive for Covid-19 while asymptomatic, which leads to the silent transmission of the disease."

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The study also found that one in 20 healthcare workers with Covid infection developed severe complications, and one in 200 died.

The study, co-authored by Dr Sergio Gómez-Ochoa, of the Cardiovascular Foundation of Colombia, is due to be published in The American Journal of Epidemiology.

The findings will be presented this week at the ESCMID Conference on Coronavirus Disease, the first major international conference on the virus, which is being hosted online from today until Friday.