HIV kit falsely cleared four victims of virus

Four people who tested negative for HIV with a faulty testing kit have been told they are infected with the Aids virus, the Department of Health revealed yesterday.

No details of the four individuals have been released, but efforts to trace their sexual contacts to offer them HIV tests are now underway.

The confirmation of the false negatives follows the re-testing of more than 20,000 blood samples tested for HIV between July1995 and March this year, with the IMX HIV 1/2 3rd generation kit.

Sir Kenneth Calman, the Chief Medical Officer, said in a statement: "I would like to extend my sympathies to [the four] individuals in what must be a very difficult situation."

The IMX kit, one of several used by the NHS, was withdrawn from sale worldwide on 25 March by its manufacturers, Abbott Laboratories Ltd in Chicago, after some European laboratories reported inaccurate results with it. A doctor in Portsmouth was among the first to query its reliability when a patient he knew to have full-blown Aids tested negative.

News of the kit's withdrawal was leaked at the start of the Easter bank holiday when clinics and GP surgeries were closed, leaving thousands of people - initial estimates suggested that up to 40,000 were at risk - desperate for more information and advice.

Aids charities were inundated with calls, and health ministers were severely criticised for sitting on information about the faulty kits for a week as the Department of Health tried to organise re-testing facilities before making an announcement.

The Department said that since July last year a total of 23,620 blood samples in the UK had tested negative using the IMX kit. All available stored samples - 20,900 - had been re-tested and four of the negative results found to be wrong.

Stored samples were not available to re-test the remaining 2,720 negative results. About 800 of these were done in NHS clinics and the people concerned had been invited to provide fresh blood samples. The remaining 1,920 samples were provided for private tests, mainly for insurance purposes and visa applications on behalf of people considered to be at low risk of HIV infection.

It is believed that only people with a very high number of antibodies to HIV in their blood were at risk of testing negative instead of positive with the IMX test. Antibody status may be related to the stage of infection with people only recently exposed to HIV and those on the verge of Aids being most likely to fit this profile.

Tom Lawson, spokesman for the Terrence Higgins Trust, said the Government had done well to carry out the re-testing of samples quickly. However, he said there were lessons to be learned about the Department's co-ordination with journalists and support groups during a public health crisis.

"Four people who re-tested positive is four people too many. We have to ensure nothing like this is going to happen again," Mr Lawson said. "It must be enormously distressing for the people concerned. This is a terrible way to learn that you are HIV positive."

A spokesman for Abbott Laboratories Ltd in Chicago said last night that more than 2.5 million tests had been carried out worldwide with the IMX kit. The company had, until yesterday, been aware of one confirmed false negative in the UK and three others in Spain and France.