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U.S. Tuberculosis cases on the decline
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admin on 03/20/2010 13:20:00
 
MORBIDITY AND MORTALITY WEEKLY REPORT (MMWR)
DECREASE IN REPORTED TUBERCULOSIS CASES --- UNITED STATES, 2009
WEEKLY
March 19, 2010 / 59(10);289-294
Every year, CDC reports results from the National TB Surveillance System for the
previous year. For 2009, a total of 11,540 tuberculosis (TB) cases were reported
in the United States. The TB rate was 3.8 cases per 100,000 population, a
decrease of 11.4% from the rate of 4.2 per 100,000 reported for 2008. The 2009
rate showed the greatest single-year decrease ever recorded and was the lowest
recorded rate since national TB surveillance began in 1953 (1). TB case counts
and rates decreased substantially among both foreign-born and U.S.-born persons,
although foreign-born persons and racial/ethnic minorities continued to have TB
disease disproportionate to their respective populations. The TB rate in
foreign-born persons was nearly 11 times higher than in U.S.-born persons. The
rates among Hispanics and blacks were approximately eight times higher than
among non-Hispanic whites, and rates among Asians were nearly 26 times higher.
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. However, increased underreporting or underdiagnosis of TB also is
possible. CDC currently is investigating possible causes for the sharp decrease
in reported TB cases. 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.
Health departments in the 50 states and the District of Columbia (DC)
electronically report to CDC the TB cases that meet the CDC/Council of State and
Territorial Epidemiologists case definition.* Reports include the patient's
race, ethnicity (i.e., Hispanic or non-Hispanic), treatment information, and,
whenever available, drug-susceptibility test results. CDC calculates national
and state TB rates overall and by racial/ethnic population using current U.S.
Census population estimates. Annual estimates were used to calculate the
national TB rate and the percentage change from 2008 to 2009. Population
denominators used to calculate TB rates and percentage changes over time
according to national origin (U.S.-born versus foreign-born persons) were
obtained from the Current Population Survey. A U.S.-born person was defined as
someone born in the United States or in its associated jurisdictions, or someone
born in a foreign country but having at least one U.S.-born parent. Persons not
meeting this definition were classified as foreign born. For 2009, patients with
unknown country of birth represented 2.0% (235 of 11,540) of total cases. For
this report, persons identified as white, black, Asian, American Indian/Alaska
Native, native Hawaiian or other Pacific Islander, or of multiple races were all
classified as non-Hispanic. Persons identified as Hispanic might be of any race.
In 2009, TB rates in the 51 reporting areas ranged from 0.4 (Wyoming) to 9.1
(Hawaii) cases per 100,000 population (median: 2.7 cases per 100,000 population)
(Figure 1). Thirty-six states and DC had lower rates in 2009 than 2008; 14
states had higher rates. Four states (California, Florida, New York, and Texas)
reported more than 500 cases each for 2009. Combined, these four states
accounted for half (50.3% [5,801]) of all TB cases in 2009.
In 2009, a total of 4,499 TB cases were reported in U.S.-born persons
(representing 39.8% of the 11,305 cases with known national origin), compared
with 5,282 reported in 2008. The 2009 rate in U.S.-born persons was 1.7 per
100,000, a decrease of 15.8% compared with 2008, and a decrease of 77% compared
with 1993 (Figure 2). In 2009, a total of 1,861 cases were reported among
blacks, representing the highest number of TB cases among U.S.-born persons and
41.4% of all U.S.-born cases in 2009. A total of 3,386 cases were reported among
Hispanics, more than any other racial/ethnic group, followed by Asians and
blacks (Table). Asians had the highest TB case rate among all racial/ethnic
groups. From 2008 to 2009, TB rates decreased for all racial/ethnic minorities.
The greatest annual decrease in TB rate was among whites (15.2%), followed by
blacks (14.0%) and Hispanics (13.6%). The smallest decrease in 2009 was among
Asians (9.0%).
A total of 6,806 TB cases were reported in foreign-born persons in 2009,
compared with 7,602 reported in 2008, a decrease of 10.5%. For 2009, these cases
represented 60.2% of all cases with known national origin, compared to 59.0% of
cases with known origin in 2008. The TB rate among foreign-born persons in 2009
was 18.6 per 100,000 population, a 9.0% decrease compared to 2008 and a 45.3%
decrease since 1993. In 2009, four countries accounted for 50.1% of TB cases in
foreign-born persons: Mexico (1,574), the Philippines (799), India (523), and
Vietnam (514).
In 2009, among persons with TB with a known human immunodeficiency virus (HIV)
test result, 10.2% (690 of 6,743) were coinfected with HIV. California and
Vermont data were not available for this calculation.†
TB cases are classified by site of disease (pulmonary or extrapulmonary) and
whether Mycobacterium tuberculosis was cultured from a patient specimen (i.e.,
culture positive or culture negative). In 2009, a total of 8,535 TB cases were
pulmonary TB, of which 7,133 (83.6%) were culture positive. Of 2,297
extrapulmonary TB cases, 1,630 (71.0%) were culture positive. Site of disease or
culture status was unknown for 708 cases. From 2008 to 2009, culture-positive
pulmonary cases decreased 13.6% (8,257 to 7,133), culture-negative pulmonary TB
cases decreased 17.5% (1,700 to 1,402), culture-positive extrapulmonary TB cases
decreased 8.3% (1,777 to 1,630), culture-negative extrapulmonary TB cases
decreased 3.1% (688 to 667), and cases with unknown site of disease or culture
status increased 48.7% (476 to 708).
Drug-susceptibility data generally are available 1 year later than provisional
surveillance data. The most recent year for which complete drug-susceptibility
data are available is 2008. Drug-susceptibility test results for isoniazid and
rifampin were reported for 96.0% (9,628 of 10,034) of culture-confirmed TB cases
in 2008, compared with 97.9% (10,251 of 10,468) in 2007. A total of 107 cases of
multidrug-resistant TB (MDR TB)§ were reported in 2008, which represented 1.1%
of all culture-positive cases with drug-susceptibility testing, compared with
1.2% [123 of 10,251 cases] in 2007. For persons with a previous history of TB,
the percentage of cases with MDR TB remained approximately four times higher
than for persons without a prior history of TB. In 2008, foreign-born persons
accounted for 77.6% of MDR TB cases. Foreign-born persons had higher percentages
of MDR TB than U.S.-born persons, both among persons with (4.3% versus 1.4%) and
without (1.0% versus 0.4%) a previous history of TB. To date, no new cases of
extensively drug-resistant TB (XDR TB)¶ have been reported in 2009.
The recommended length of drug therapy for most types of TB is 6--9 months. In
2006, the latest year for which end-of-treatment data are complete, 83.7% of
patients for whom