LONDON (BLOOMBERG) - A large proportion of UK healthcare workers may have been infected with coronavirus early in the pandemic, according to a survey suggesting that loss of smell and taste may be a guide to determining its prevalence in populations.

About two-thirds of the London National Health Service staffers surveyed reported diminished ability to taste or smell - one of the prominent, early symptoms of Covid-19 - just weeks after the coronavirus arrived in the UK, according to research published on Thursday (Aug 6) in The Lancet Microbe journal.

Healthcare professionals on the front lines are far more likely to contract the virus compared with individuals in the general community, earlier studies have found.

Yet it's unclear how many NHS staff have contracted the virus as testing has been limited. The high rate of the loss of smell, called anosmia, suggests that a larger proportion may have been infected than previously thought.

"Some people get smell loss before other symptoms, or as the only symptom," of Covid-19, said Carl Philpott, professor of rhinology at the University of East Anglia's Norwich Medical School, in an interview.

"It has a sudden onset, so people really notice the difference."

Anosmia should be used more frequently to identify Covid-19 outbreaks and patients, Philpott said.

Data from coronavirus tracking apps has shown that smell loss and fatigue are more likely to occur than cough and fever in patients, he said.

Philpott said he's collected more data showing that anosmia was widespread among health workers in other UK regions, including including Norfolk and the North West.

Greater recognition of the early symptom might allow more infected people to be isolated early on, rather than spreading the virus unaware of their status, he said.

People who experience the symptom also risk longer term sensation deficits, he said.

"We think about 60 per cent of people with coronavirus are experiencing smell loss and 10-15 per cent of those have permanent smell loss that doesn't resolve in 3-4 weeks," he said. "These are unprecedented numbers."

The survey was completed by 242 health workers in the week ending April 23, before the UK officially added smell loss to Covid-19's symptoms on May 17.