U.S. Tuberculosis Rate Falls to Record Low, Possibly Due to Improved Testing of Immigrants

The prevalence of tuberculosis (TB) cases on the U.S. fell by more than 10% from 2009 to 2008 -- the greatest single-year decrease ever recorded and the lowest rate since TB surveillance began in 1953, according to the latest data from the CDC's National TB Surveillance System reported in the March 19, 2010 issue of Morbidity and Mortality Weekly Report.

Each year the Centers for Disease Control and Prevention (CDC) reports results from the National TB Surveillance System for the previous year. Preliminary surveillance data are available for 2009; drug resistance data are typically available 1 year after surveillance data.

Summary Findings

·      A total of 11,540 TB cases were reported in the U.S. in 2009, compared with 12,904 in 2008.

·      The 2009 TB rate was 3.8 cases per 100,000 people, a decrease of 11.4% from the rate of 4.2 per 100,000 reported for 2008.

·      TB case numbers and rates decreased substantially among both U.S.-born and foreign-born individuals:

o      Foreign-born TB cases declined to 6806, or 18.6 per 100,000 people, a drop of 10.5% from 2008

o      U.S.-born TB cases fell to 4499, or 1.7 per 100,000 people, a decrease of 15.8% from 2008.

·      Foreign-born people continued to have disproportionately high TB rates compared with U.S.-born people:

o      The TB rate of foreign-born people was nearly 11 times higher than that of U.S.-born people.

o      Foreign-born people accounted for 60.2% of all U.S. TB cases in 2009.

·      Among U.S.-born people, non-white racial/ethnic groups continued to have disproportionately high TB rates:

o      TB rates among black and Hispanic people were approximately 8 times higher than that of non-Hispanic whites.

o      Blacks, accounted for the 41.4% percent of all U.S.-born TB cases in 2009.

o      Hispanics had the largest total number of TB cases (3386).

o      Asians had the highest TB rate (23.4 per 100,000 people), nearly 26 times higher than that of whites.

o      Whites saw the largest annual TB rate decrease in 2009 (15.2%), followed by blacks (14.0%), Hispanics (13.6%), and Asians (9.0%).

·      By state, 2009 TB rates ranged from 0.4 per 100,000 people in Wyoming to 9.1 per 100,000 in Hawaii.

·      36 states and Washington, D.C. had lower rates in 2009 compared with 2008, while 14 states had higher rates.

·      4 states (California, Florida, New York, and Texas) reported more than 500 cases each in 2009, and together accounted for 50% of all TB cases.

·      4 countries accounted for 50% of TB cases in foreign-born people: Mexico (1574), Philippines (799), India (523), and Vietnam (514).

·      10.2% of people with TB who had a known HIV test status were HIV/TB coinfected.

·      A total of 107 cases of multidrug-resistant TB (MDR TB) were reported in 2008, represented 1.1% of all culture-positive cases with drug-susceptibility testing.

·      To date, no new cases of extensively drug-resistant TB (XDR TB) were reported for 2009.

"The large decrease in reported cases during 2009 might represent a decrease in TB disease resulting from changes in population demographics or improved TB control," the investigators stated. "However, increased under-reporting or under-diagnosis of TB also is possible."

"CDC currently is investigating possible causes for the sharp decrease in reported TB cases," they continued. "Diagnosing and reporting all TB cases is essential to ensure treatment of patients with TB and implementation of other public health interventions that interrupt transmission."

One possible explanation for the large decrease may be changes in pre-immigration TB testing requirements implemented in 2007, according to an accompanying editorial note. Prospective immigrants suspected of having pulmonary TB based on a chest X-ray must now also receive a culture test of a respiratory specimen, rather than the less sensitive microscope smear test. Potential immigrants with TB are required to receive treatment and must be determined to no longer be infectious before the can enter the U.S.

Rate (per 100,000 population) of tuberculosis (TB) cases, by state/area - United States, 2009 (Source: National TB Surveillance System)



C Winston, R Pratt, L Armstrong, and T Navin. Decrease in reported tuberculosis cases - United States, 2009. Morbidity and Mortality Weekly Report (MMWR) 59(10): 289-294 (Free full text). March 19, 2010.