A survey from London hospitals has shown that patients who are diagnosed with both HIV and tuberculosis (TB) are among the most difficult group to treat. The study looked at 188 London patients diagnosed with TB and HIV between 1996 and '99. Four out of 10 had no idea they were HIV positive when diagnosed with TB. Most had advanced HIV illness: their average CD4 count was 94, and 39 per cent fell ill with Aids while they were on TB therapy. The study's authors recommended that HIV/TB co-infected patients with CD4 counts under 100 should be started on HIV therapy immediately - regardless of the risk of side effects.

In practice, however, over half were not prescribed HIV therapy while on TB treatment, because patients receiving TB and HIV therapy together were almost twice as likely to experience bad reactions to HIV drugs. The women in the group were four times more likely. This meant that either the TB or the HIV therapy had to be stopped. Bad reactions to TB drugs mainly occurred in the first two months of therapy, so the study's authors suggested that HIV therapy could be delayed for two months in all but the most immune-compromised patients

A US study has shown that, alone among Aids-defining infections, TB has not become less common since 1996. A Spanish study has shown that TB/HIV co-infected patients with CD4 counts under 100 are much more likely than others to develop multi-drug-resistant TB. And a New York study says that HIV/TB co-infected patients are four times more likely to fail their therapy, and recommends TB treatment should be maintained for as long as a year.