'People should not be alarmed. We are confident the risk is almost zero,' a department spokesman said. 'We are working with other countries to get information as soon as possible to see how different testing kits perform against this new strain.'
Scientists in France and Belgium have so far detected the mutant strain of HIV in 11 patients and found that several kits, including ones used in Britain, failed to detect antibodies to the virus or gave ambiguous results.
The French health authorities have recalled one blood test and ordered an urgent re-evaluation of others used by their blood transfusion service, as revealed yesterday by the Independent on Sunday.
Health officials in Britain have contacted Murex Diagnostics, the manufacturers of the blood test most commonly used in the UK, to see how to improve the test kit's ability to detect antibodies to the group O strain of HIV, which emerged in the west African state of Cameroon a few years ago.
Officials from Murex flew to Paris two weeks ago to be briefed by Francois Simon, the virologist at the Bichat Claude Bernard Hospital, who identified the new strain in French patients. A spokesman for Murex was unavailable for comment.
Dr Simon said current test kits were very good at detecting antibodies to typical strains of HIV, but were more inaccurate in picking out less-common variants, such as those belonging to group O.
The situation is reminiscent of the decision in 1990 to introduce tests for HIV-2, the second major family of HIVs, as a result of the accidental discovery that a blood donor in Britain was infected with the HIV-2 virus.
Dr Simon said that of the 10 French patients with the group O strain of HIV, nine had lived in Cameroon, where scientists estimated that between 5 and 10 per cent of HIV-positive people are infected with that strain.
The tenth patient was a French woman who worked as a barmaid in a garrison town in the east of France where some of the soldiers may have spent time in Cameroon. He said the risk of a blood donor infected with group O HIV in Britain or France was 'very, very low'.
Professor John Cash, director of the Scottish Blood Transfusion Service, said all potential blood donors were asked whether they had visited Africa or had had sex with someone from that continent. This was the first line of defence against contamination by a mutant strain of HIV.