The race is on to identify one of the first people in the UK believed to have contracted a Brazilian strain of coronavirus.
Public Health England (PHE) said on Sunday that six cases of the P1 variant first detected in the city of Manaus have been found in the UK – three in England and three in Scotland.
But one of the cases in England has not yet been identified, with PHE saying the person did not complete their test registration card, leaving out their contact details.
Two of the three English cases were confirmed in South Gloucestershire but the third could be anywhere in the nation.
Anyone who took a test on 12 or 13 February and has not received a result, or has an uncompleted test registration card, is being asked to come forward immediately, as health officials try to track down the individual.
The Gloucestershire cluster was said to originate from one individual who travelled back from Brazil and arrived in London on 10 February – five days before the government’s quarantine hotel policy came into force.
PHE and NHS Test and Trace are contacting the passengers on Swiss Air flight LX318 travelling from Sao Paulo, through Zurich, and landing in London Heathrow on that date.
Surge testing will be carried out in the Bradley Stoke, Patchway and Little Stoke areas of South Gloucestershire.
The remaining unlocated case is not believed to be linked to the others because the virus was found to have slight genetic differences.
Officials said the individual’s test was processed on 14 February, so believe it is likely they took it a day or two earlier.
The Scottish government said three residents who returned to north-east Scotland from Brazil, via Paris and London, subsequently tested positive for the Manaus variant of COVID-19.
Officials are contacting the other passengers on their flight from London to Aberdeen. The cases are not thought to be connected to the three confirmed cases in England.
There are currently four variants of concern: the UK/Kent variant, the UK/Kent variant + E484K mutation, the South African variant, and the Brazilian variant.
Read more: What do we know about coronavirus variants?
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