Twice as many people were diagnosed with both HIV and tuberculosis in 2007 than were in 2006, according to a report released today by the World Health Organization (WHO). But the dramatic increase comes from improved surveillance, not an actual rise in cases, the report stresses.
Mycobacterium tuberculosis, the bug that causes TB, infects one-third of the world's population, but it usually causes no harm. And even people with "active" TB typically confine the infection to the lungs and can be cured with antibiotics. HIV, which destroys the immune system, helps TB in several ways, turning latent TB infections active and allowing the bug to spread outside the lungs. In addition, the drugs used to treat HIV can interfere with TB antibiotics.
In 2006, 700,000 people were diagnosed with both HIV and active TB, and 28% of those people died, making TB the leading cause of death in HIV-infected people.
But the new report recognizes that those figures badly underestimate the actual extent of the problem, leading to seemingly much more dire numbers for 2007. According to Global Tuberculosis Control 2009, released on World TB Day (24 March), 9.27 million people developed active cases of TB that year, and 1.37 million of these people also had HIV infections. TB killed 1.8 million people in 2007, with the HIV-infected accounting for one-fourth of those deaths. "We now have very good and certainly much better data than before showing the incredible impact of HIV on tuberculosis and particularly TB-related deaths," says epidemiologist Richard Chaisson, who directs the Johns Hopkins University Center for TB Research in Baltimore, Maryland, and who was not involved with the WHO report.
The jump in coinfections is primarily due to improved surveillance. Many more TB clinics now test for HIV infection, notes the report, and in 2007 WHO relied on data from four times as many of these clinics as it did in 2006. WHO also emphasizes that back calculations for previous years indicate that the number of new HIV/TB cases actually peaked in 2005 at 1.39 million, slightly above this year's figure.
All told, the number of new TB cases per capita has dropped slightly from a peak of 142 cases per 100,000 in 2004 to 139 per 100,000 in 2007. TB prevalence--which combines new cases with active ones from previous years--also dropped from 13.9 million in 2006 to 13.7 million in 2007. But Chaisson says he suspects these numbers still underestimate the actual problem. "They're working with the best stuff they have, and the best stuff they have is not good," he says.
Chaisson and others stress that global donors must do more to support TB control programs that integrate HIV prevention and treatment. A second report issued today by Advocacy to Control TB Internationally, a partnership of advocates from eight countries, claimed that the four largest TB funding donors--including the U.S. President's Emergency Plan for AIDS Relief and the Global Fund to Fight AIDS, Tuberculosis and Malaria--made it difficult to discern where they spent money on HIV/TB and whether the programs were effective. "It's impossible to say what the four are collectively providing," says Paul Jensen, who helped write the report and is the global research coordinator for the TB campaign led by RESULTS Educational Fund, a nonprofit advocacy group based in Washington, D.C.
More funding is necessary, Chaisson and other TB specialists say, to improve TB diagnosis and treatment. The most commonly used diagnostic tests were developed decades ago, says Chaisson, and miss roughly half the cases of active TB in HIV-infected people. The field also desperately needs new anti-TB drugs, as resistance has developed against all of the commonly used antibiotics. According to the WHO report, multidrug-resistant TB--against which the two first-line drugs do not work--accounted for 500,000 cases in 2007. "Extensively" drug resistant TB cases, which do not respond to many second-line treatments and were first described in 2006, now have been reported by 55 countries.
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