TB rate down in U.S., but drug-resistant cases rise elsewhere

Even with tuberculosis cases falling sharply in the United States to historic lows, strains of drug-resistant disease are gaining ground elsewhere in the world, the Centers for Disease Control Prevention and the World Health Organization report.

The CDC said March 18 that TB prevalence in this country dropped 11.8 percent last year, the largest yearly decline since the government began monitoring the disease in 1953. But on the same day, the World Health Organization reported that an estimated 440,000 people worldwide had multi-drug-resistant tuberculosis (MDR-TB) in 2008, and a third of them died.

Nearly half of the cases were in China and India, which have been hit hardest by the outbreak. In Africa, estimates show 69,000 cases emerged, the vast majority of which went undiagnosed, the WHO reported.

In some areas of the world more than one in every four cases of tuberculosis result from the hard-to-treat strain.

For example, 28 percent of all people newly diagnosed with TB in one region of northwestern Russia had the multidrug-resistant form of the disease in 2008. This is the highest level ever reported to the WHO. Previously, the highest recorded level was 22 percent in Baku City, Azerbaijan, in 2007.

Overall, there were 9.4 million new TB cases in 2008 and 1.8 million deaths, so the drug-resistant strains are a relatively small problem. But experts fear that they will displace conventional strains of the TB mycobacterium, vastly complicating treatment.

Conventional TB treatment costs about $20 and requires six months. The drug-resistant strains can cost as much as $500 to treat and take as long as two years.

The CDC said there were 11,540 U.S. TB cases reported in 2009, 40 percent of them in people born in this country. The rate of disease was 11 times as high in foreign-born people as in native-born Americans. The rates in blacks and Latinos were eight times as high as the rate in whites, and the rate in Asians was 26 times as high.

A total of 108 U.S. cases of multi-drug-resistant TB were reported in 2008, the most recent year for which data are available.

Experts suspect that the sharp decline in TB cases is related both to improved screening for the disease among potential immigrants and the weak economy, which has slowed immigration and caused many immigrants to return to their homes soon after arrival.

The California Department of Public Health said the state had seen the largest decline in TB cases since 2000: an 8.6 percent drop to 2,472 cases.

In the new WHO's Multidrug and Extensively Drug-Resistant Tuberculosis: 2010 Global Report on Surveillance and Response, officials said there are encouraging signs that even in the presence of severe epidemics, governments and partners can turn around MDR-TB by strengthening efforts to control the disease and implementing WHO recommendations.

The WHO is engaged in a five-year project to strengthen TB laboratories with rapid tests in nearly 30 countries. This will ensure more people benefit early from life-saving treatments. It is also working closely with the Global Fund to Fight AIDS, Tuberculosis and Malaria and the international community on increasing access to treatment.

Previous reports found high levels of mortality among people living with HIV and infected with MDR-TB and XDR-TB. In KwaZulu Natal in South Africa, an outbreak of XDR-TB killed 52 out of 53 people, most of whom were HIV positive, within three weeks.

The report highlights several reasons why drug-resistant TB may be associated with HIV, particularly in some Eastern European countries. However, more research is needed to determine whether there is an overlap between the MDR-TB and HIV epidemics worldwide.

MDR-TB is caused by bacteria that are resistant to at least isoniazid and rifampicin, the most effective anti-TB drugs. MDR-TB results from either primary infection with resistant bacteria or may develop in the course of a patient’s treatment.

Extensively drug-resistant TB (XDR-TB) is a form of TB caused by bacteria that are resistant to isoniazid and rifampicin (i.e. MDR-TB) as well as any fluoroquinolone and any of the second-line anti-TB injectable drugs (amikacin, kanamycin or capreomycin).

These forms of TB do not respond to the standard six-month treatment with first-line anti-TB drugs and can take up to two years or more to treat with drugs that are less potent, more toxic and much more expensive.