After more than 2,000 NHS staff across Hertfordshire were tested to see if they have had COVID-19 – one in five tested positive for having had the virus.

The data – presented to the board of the Herts Valleys Clinical Commissioning Group (CCG) last week shows that by July 1, 12,268 staff had been tested for antibodies with 2,424 – or 19.75 per cent – testing positive.

The snapshot of testing, which was scheduled to continue until July 10 as part of a national study – also suggests that infection rates vary between trusts.

At West Hertfordshire NHS Hospitals Trust – which operates Watford General, St Albans City and Hemel Hempstead hospitals – 34 per cent of the 2,790 staff tested were found to be positive for the COVID-19 antibody.

Meanwhile at Hertfordshire NHS Comunity Trust – which provides services in clinics, schools and community hospitals – eight per cent of the 1,362 staff tested were positive.

At the East and North Hertfordshire NHS Trust – which operates Stevenage’s Lister, Hertford County, Welwyn Garden City’s New QEII hospitals and the Mount Vernon Cancer Centre – 15 per cent of the 4,498 staff tested were positive.

Nineteen per cent of the 537 staff tested at the Central London Community Healthcare Trust and the Hertfordshire Partnership Foundation Trust, with 3,081, were also positive.

A spokeswoman for the NHS in Hertfordshire stressed that it was not unusual for antibody rates to vary between trusts as they are different facilities with varying conditions treated.

She said: “Acute hospital trusts across the East of England region have seen different rates of antibody prevalence of between 20 and 40 per cent – so the Hertfordshire area is not unusual in its prevalence of the virus.

“We can’t compare the other local Hertfordshire NHS Trusts with each other because these trusts do not provide facilities for critically ill patients or manage the same types of patients as the acute trusts.

“Therefore, their staff would have had different rates of contact with the virus than the acute hospitals.

“In general those that have experienced symptoms suggestive of a COVID-19 infection are more motivated to get tested which ends up skewing the overall results until they are adjusted to take this into account and these are raw unadjusted figures.”

The national testing is also due to open up to opticians and pharmacists, with testing for home care and social care staff to follow.

In addition the data presented to the CCG board also shows that 13 per cent of tests on 933 staff working in primary care in West Hertfordshire tested positive.