The incidence of tuberculosis infections in the United States dropped by an unusual and unexpectedly large 11.4% in 2009, the largest one-year decrease since federal agencies began tracking the disease in 1953, the Centers for Disease Control and Prevention reported Thursday in its Morbidity and Mortality Weekly Report. The largest previous drop was 11.1% in 1956. Since 2000, the rate has declined by an average of 3.8% annually, so the large decrease last year seemingly came out of the blue.
In 2009, a total of 4,499 TB cases were reported in U.S.-born people, with the rest in immigrants. The rate in native Americans was 1.7 cases per 100,000 people, a 15.8% decrease from the previous year and a 77% decrease since 1993. The rate in foreign-born people was 11 times higher than that in native Americans. Ethnic minorities also suffered more heavily. The rates in blacks and Hispanics were about eight times higher than in whites, while the rate in Asians was 26% higher. A total of 107 cases of multidrug-resistant TB were reported in 2008, the most recent year for which data are available. Such cases are resistant to isoniazid and rifampin, the two drugs most commonly used to treat TB. No cases of extensively drug-resistant TB, the most dangerous form of the disease because it is extremely difficult to treat, were reported in 2009.
Experts are mystified about the sharp drop in cases in 2009. Although it may be due in part to under-reporting or under-diagnosis, that seems unlikely given the past history of monitoring. Beginning in 2007, however, new rules for pre-immigration screening for TB were instituted, which required sputum cultures for TB diagnosis in potential immigrants who are suspected of having TB and pre-immigration treatment of those identified. The decreases might also have been a result of the poor economy, which led to reductions in immigration and increases in recent immigrants returning to their home countries, particularly Mexico. Anecdotal reports from state and local health departments indicate they have seen fewer TB patients who are recent immigrants.
Four states -- California, Florida, New York and Texas -- reported having more than 500 TB cases each for 2009. Combined, these four accounted for 50.3% of all cases reported that year.
[Updated: 3 p.m. The number of TB cases in California dropped by the largest margin in nearly a decade, the California Department of Public Health said Thursday. In 2009, 2,472 cases of TB were recorded in the state, a decrease of 8.6% from 2008. The decline was the largest since 2000. About three-quarters of the cases were among people bornin other countries.]
-- Thomas H. Maugh II