31% of African TB now due to HIV epidemic

A new WHO study of the burden of tuberculosis has found that most of the world's largest and fastest-growing epidemics of TB, in Africa, are increasingly attributable to the effects of HIV.

The researchers, based at the London School of Hygiene and Tropical Medicine, use mathematical models to compile and assess information from published studies and a network of experts to estimate that 9% of the estimated 8.3 million new cases of TB in the year 2000 would not have happened, but for HIV. (They stress that all of their figures are subject to uncertainty: for example, the range for those just given is 7% to 12% out of a total of 7.3-9.2 million.)

However, this proportion rises to 31% in Africa south of the Sahara, the region with the highest proportion of people living with HIV. It is no coincidence that this is also the WHO region with the highest global TB incidence, at 290/100,000 people per year, and the fastest-growing case load, increasing by 6% per year.

Half of all new TB cases, 4.4 million, were in five Asian countries where only a small proportion are currently attributed to HIV: India, China, Indonesia, Bangladesh and Pakistan. In all five countries, TB rates declined between 1997 and 2000. However, in India 3.4% of TB cases and 4.8% of TB deaths are due to HIV - and the total number of co-infected people in Asia exceeds 2 million.

In Southern Africa, the balance looks very different. In South Africa, 50% of tuberculosis cases (and almost 59% of TB deaths) are attributed to HIV and the number of people co-infected with HIV and MTb is 2 million - 8.3% of the adult population. South Africa's TB incidence grew by 8.7% per year between 1997 and 2000. Other countries in the region, from Namibia and Botswana through to Zimbabwe, Zambia, Malawi and Mozambique, have problems on a similar or even greater scale.

Although absolute figures are much smaller in more developed countries, the impact of HIV on TB is very substantial in the USA, where 26% of TB cases are attributed to HIV, and even in parts of western Europe such as Spain, where both diseases are concentrated among injecting drug users.

In contrast, the largest European epidemic, in Russia, has yet to show any connection between HIV and TB. (This is likely to change dramatically, however, considering the rates of both diseases among populations of injecting drug users and prisoners.)

The report notes that the most successful public health campaigns against TB in recent years - in China, Peru and Vietnam - have been in countries with relatively low levels of HIV. It stresses that TB can still be treated where HIV is widespread but admits that turning the epidemic around will require more than the WHO DOTS programme. ARV treatment for HIV is identified as one of a number of measures that can reduce the rate of active TB among those exposed to TB and also save lives among those who do have active TB.

"There is urgent need to implement a strategy of extended scope combining intensified TB case finding and treatment, HIV prevention, and the identification and treatment of latent MTB in coinfected individuals. Controlling HIV-related TB will require a massive global effort. The estimates in this article provide a measure of this challenge, and suggest ways to monitor the impact of efforts to control HIV-related TB."