Health officials in Hertfordshire are understood to be examining around 240 cases in the week to October 3 where people who tested positive and were included in its figures were living in postcodes outside the county.
Many of them could be students. The officials are also examining figures for the following week to see if the problem continued.
In the St Albans district, out of around 110 cases in that seven-day period, some 50 are believed to be students living elsewhere.
Chris White, leader of St Albans district council, stressed: “Just under half of the cases turned out to be due to students at university outside of Hertfordshire.
“This level of discrepancy could make a significant difference to policy making.”
Jim McManus, director of public health at Hertfordshire county council, said: “There is a nationwide issue with some students’ positive coronavirus tests being attributed to their permanent home address rather than their term-time address, and this is undoubtedly having an impact on the reported figures for Hertfordshire.”
The problem first emerged in Richmond after the borough saw cases soar to give it the highest Covid-19 rate in London, though now officials believe more than 16 per cent of the cases may be students outside the area.
The errors mean some local authority areas with universities could have their case numbers appearing lower than they really are because students will be linked to their family addresses, although they are encouraged to register with a GP in their university area.
The problem is understood to be due to a “data enrichment” process in which data of people who test positive is run through NHS databases to identify any problems such as missing contact details. This can reportedly override addresses given by people at test centres.
A government spokesman said: “NHS Test and Trace uses the most up-to-date information available, including the address held by their GP, and the postcode provided when someone registers for a test. This information is provided to the relevant local authority and helps minimise any discrepancies in local data.”
