A large proportion of UK healthcare workers may already have been infected with Covid-19, according to new research led by the University of East Anglia in collaboration with University College London.
In May, Public Health England added a new loss of taste or smell (anosmia) to the list of symptoms for Covid-19.
Research published today in The Lancet Microbe finds a high prevalence of anosmia cases among healthcare workers between mid-February and mid-April.
Senior author Prof Carl Philpott, from UEA's Norwich Medical School, said: "Smell loss as a symptom of Covid-19 is particularly important for healthcare professionals because they are at the frontline of pandemic - and at high risk of both contracting and spreading the virus.
"In many cases smell loss can be the only symptom of Covid-19, or accompanied by mild symptoms.
"We wanted to find out how widespread smell loss has been among healthcare workers."
The research team distributed questionnaires to staff at London's Barts Health NHS Trust - one of the largest NHS trusts in the UK.
The questionnaire was completed by 262 healthcare workers in the week April 17-23. At this time, anosmia was not yet listed as an official symptom and covid-19 testing among NHS workers was still limited to those displaying symptoms of a new continuous cough and/or a high temperature (>37.8°C) as per national guidance.
Nevertheless, 73 (27.9 per cent) of the participants had been tested for Covid-19, with 56 of these (76.7 per cent) confirmed positive.
In line with Public Health England guidance at the time of the study, staff who only had anosmia as a symptom would not have been required to isolate or be eligible for testing. Like other trusts, staff testing for Covid-19 at Barts Health has been available since late March 2020. Loss of smell was included as a symptom in national guidance since May 18 2020 and any staff with that symptom are required to have a test
and self-isolate for seven days.
Prof Philpot said: "The really interesting thing that we found was that 168 of the participants - nearly two thirds - said that they had lost their sense of smell or taste at some point between mid-February and mid-April.
"We also found a strong association between smell loss and the positive Covid-19 test results, with those who had lost their sense of smell being almost five times more likely to test positive.
"This suggests that a large proportion of healthcare workers may have already been infected with Covid-19, with only mild symptoms.
"We conducted this research at Barts Health, however we would expect to see similar results from other NHS trusts too.
"Cases like this most likely went undiagnosed at the time because of a lack of awareness about smell loss as a symptom.
"This is really important because healthcare professionals are at the frontline of the pandemic and are at high risk of both contracting and spreading coronavirus.
"There is a need for awareness and early recognition of anosmia as a means to identify, urgently test and isolate affected healthcare workers in order to prevent further spread of disease," he added.
Rupert Pearse, clinical director for research and development at Barts Health NHS Trust said: "We're delighted to play a central role in supporting key research studies which help us better understand Covid-19. We know that NHS trusts that carry out research deliver better quality patient care and we are one of the leading contributors to clinical research across the NHS.
"Our staff have also volunteered to participate in a variety of important projects too and we are pleased to be able to support studies that focus on our healthcare workers."
The study also involved a follow-up survey in May, in which 47 per cent of respondents reported that their sense of smell and taste had completely recovered. A further 42 per cent said they had partially recovered their sense of smell and taste, but just over 7 per cent still suffered anosmia.
The survey has also been running in two Norfolk hospitals and in two hospitals in the North West with the responses of over 1,000 healthcare workers due to be published soon.
The research was led by UEA in collaboration with Whipps Cross University Hospital (part of Barts Health NHS Trust), University College London, the Royal National ENT and Eastman Dental Hospitals (part of UCLH NHS Foundation Trust) and the Norfolk Smell & Taste Clinic, at Norfolk & Waveney ENT Service.
'Anosmia/hyposmia in healthcare workers with a SARS-CoV-2 infection' is published in The Lancet Microbe on August 6, 2020.
Peer reviewed - survey - people