Defective medical tests

Over 1 million people who were tested for the HIV virus in 1995 and 1996 were told that if they tested negative they would have to be retested because the particular brand of test was faulty. Four known HIV carriers produced negative test results, so the test was withdrawn in Britain, Germany, France, Spain, Denmark, Switzerland, Greece and the Netherlands. The chances of a false negative were 1 in 1000, as the test gave incorrect readings only for those with very high levels of HIV virus in their blood.