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 U.S. Centers for Disease Control and Prevention said Thursday that TB prevalence in this country dropped 11.8% 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 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. But in some areas of the world, especially three provinces in Russia, more than 1 in every 4 cases of tuberculosis result from the hard-to-treat strain.
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% 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% drop to 2,472 cases.