A team of 40 people, armed with just a single bar code and limited test data, spent days using "dogged determination" to track down the mystery person in the UK infected with the Manaus coronavirus variant.
Data analytic experts and laboratory and logistic resources were drafted in to help identify the individual who tested positive for the variant of concern, with the team narrowing in on them among thousands of potential households.
Three cases of the P1 variant, first identified in the Brazilian city of Manaus, were detected in England on 26 February, along with three more in Scotland.
A public appeal was launched for one of those people to come forward after they left no contact details.
The P1 variant, which was also detected in travellers from Brazil to Japan, was associated with a surge of cases in Manaus late last year.
It is among a total of four variants of concern being tracked by scientists in the UK.
Speaking at a Downing Street press conference, Public Health England's Dr Susan Hopkins detailed how the person was successfully found.
She explained that the unnamed person, who lives in Croydon, south London, had attempted to register his test online, but "had failed to do so effectively".
Dr Hopkins continued: "Specialist teams from NHS Test and Trace and Public Health England immediately launched an investigation to identify the individual concerned.
"An incident team of 40 people from across the system made up of laboratories, logistics, data analytic experts was mobilised to trace the individual.
"The team began with very little information."
She said, on Sunday morning, they were only in possession of a single barcode and the date and time that the test was processed at the Cambridge Lighthouse laboratory.
The discovery, via reading the test barcode, that the sample had arrived at the Cambridge Lighthouse through the DHL service for home delivery helped narrow it down to two regions made up of 10,000 possible households.
Even though NHS Test and Trace delivers "many thousands" of kits a week, the team were able to compare the test in question to others in the system and work "backwards" from when it arrived in the laboratory, to which testing hub it had come from and through the postal service.
Their intelligence was then "overlaid with the geographical spread to look for the correlation of sequential barcodes", Dr Hopkins said.
Once the region and "time window" for the test were combined, experts tracked down "every single" distribution centre to filter down options.
These were narrowed to 379 households with "enhanced contact tracing" then kicking-in, with call handlers phoning and emailing those who could have received a test in that time interval.
This scaled it down to 27 individuals who received further calls and text messages.
Dr Hopkins said: "On Wednesday at 3pm, an individual phoned the 119 service.
"They were able to give the missing barcode number that they had held securely for the whole time.
"This individual has been interviewed extensively and lives within a household that had recently returned from Brazil and all had quarantined at home.
"Further precautionary testing will occur in the neighbourhood and we have already started testing all of the samples from the neighbourhood through whole genome sequencing to ensure there is no further distribution of cases in the community."
She added: "This is a testament to the NHS Test and Trace teams, the call handlers and the Public Health England health protection team working together to find an individual and prevent further transmission."
UK Health Secretary Matt Hancock also hailed the "brilliant" team who had been "working so hard over the past week".
He said: "Using the latest technology and with the dogged determination of our Testing and Tracing scheme, we have successfully identified the person in question.
"The best evidence is that this person in question stayed at home and there is no sign that there's been any onward transmission but as a precaution we are putting more testing in in Croydon where they live to minimise the risk of spread."