``There is still insufficient understanding of the close link between TB andHIV,'' says Peter Piot, executive director of UNAIDS. ``The two epidemicswork hand in hand. In some parts of Africa, their deadly synergy hasquadrupled the number of TB cases over the past 10 years,'' he says. UNAIDSdecided to join the `Stop TB' Initiative, a programme sponsored by the WorldHealth Organization (WHO), which is also a co-sponsor of UNAIDS. Theinitiative was launched on March 24, the World TB Day.

About a third of the world's population (around 2 billion people) carry theTB bacteria but most never develop the active disease. ``Usually no morethan 10 per cent of the people infected with the TB bacteria develop thedisease,'' says Piot. ``However, that is changing. HIV severely weakens thehuman immune system making people highly vulnerable to diseases such as TB.When healthy carriers of TB bacteria get HIV infection, their risk ofdeveloping active TB increases by a factor of over 30.''

More than 33 million people worldwide are infected with HIV. Ninety five percent are in developing countries, where the highest rates of TB infectionare found. And about 11 million people are dually infected with TB and HIV.For example, in South Africa and Uganda, half of all the TB patients arealso HIV positive. In Zambia, one in five is infected with HIV, and new TBcases have increased from 7,000 a year in 1984 to 40,000 in 1995, with anestimated 30,000 of the new TB cases due to HIV.

In Asia, the TB-HIV epidemic is causing concern. Almost 70 per cent of allthe TB cases are concentrated in Asia. In Cambodia, a estimated 20 per centof the TB patients are HIV positive, while in India, 60 per cent of AIDSpatients have TB. In Thailand too, TB has become the most common infectionamong AIDS patients.

The TB epidemic, some of it related to HIV, is also resurfacing inindustrialised nations, where were once thought to have become TB-free. Anadditional danger in developed and developing countries alike is theemergence of new strains that may resist many antibiotics, and cannot bereadily or cheaply treated.

In addition to affecting the poorest and most vulnerable, TB is a severeobstacle to the development since it hits society's most economically activegroup-those aged between 15 and 45. ``The cost of inaction will be veryhigh,'' Piot says.

TB, unlike HIV, can be treated and often cured. A simple strategy ofDirectly Observed Treatment Short-course (DOTS) has achieved cure rates of80 per cent and costs as low as Rs 450 to Rs 900 per patient. If leftuntreated, a person with infectious TB will infect between 10 to 15 peopleper year.