People have been urged to keep getting tested for coronavirus, despite a spate of positive rapid Covid tests being followed by negative PCR tests.
Public health bosses are investigating an upturn in people who have been getting a positive result in lateral flow tests and then a negative result when they get the results of samples sent to laboratory tests.
Those lab-based PCR tests are generally seen as the 'gold standard' for test results.
The UK Health Security Agency, which has replaced Public Health England, is investigating after it was made aware of false positives in a number of areas in the country.
Many of the reports stemmed from south west England, but there have been anecdotal reports of people in Norwich getting false positives.
Dr Louise Smith, director of public health in Norfolk, said she was aware of the "sporadic cases" nationally, but urged people to keep making use of tests.
She said: “While we are aware of sporadic cases nationally in which some batches of lateral flow test kits may deliver false positives, these are very rare and when used properly lateral flow tests remain reliable.
"A PCR test can be arranged to confirm any positive from a lateral flow test – just visit www.norfolk.gov.uk/covidtesting to book.”
Public health bosses say people who do get positive lateral flow test results should self-isolate and arrange the PCR test.
If people's tests come back as negative, they can stop isolating, but positive PCR tests mean people would need to complete their isolation period.
Virus expert Prof Paul Hunter, from the University of East Anglia's Medical School, said: "One of the possibilities around the false positives is that the tests are picking up another coronavirus - the common cold - which might be coming back harder.
"And if that is the case, then we might be in a position where were are excluding children from school because they have a cold, rather than coronavirus."
Another theory for the spate of false positives is that a batch of the tests could be faulty.
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