While the number of tuberculosis (TB) cases reported nationally has decreased each year since 1993, the incidence of TB in Minnesota has increased significantly during the same time period. In 2002, 237 new cases of TB disease (4.8 cases per 100,000 population) were reported statewide. This is comparable to the 239 cases (4.9 cases per 100,000) reported in 2001, the largest number of cases reported since the early 1970s.
The epidemiology of TB in Minnesota is distinct. The most significant factor is the very high percentage of TB cases that occur among foreign-born persons. In 2002, 181 (76%) cases occurred in persons born outside the U.S. For the first time since 1993, however, the percentage of foreign-born TB cases in Minnesota declined slightly in 2002, from 81% in 2001 and a high of 82% in 2000 (Figure 7). These data reflect the unique and changing demographics of immigrant populations arriving in the state, particularly persons from regions of the world where TB is prevalent. The most common regions of origin for foreign-born persons with TB disease reported in 2002 include sub-Saharan Africa (e.g., Somalia and Ethiopia) (56%) and South/Southeast Asia (e.g., Laos and Vietnam) (27%). The percentage of foreign-born TB case-patients who originated from sub-Saharan Africa decreased (from a peak of 61% in 2001) for the first time since 1993, when such data first were reported (Figure 8). (Similarly, data from the MDH Refugee Health Program indicate that the number and percentage of new refugees who arrived in Minnesota from sub-Saharan Africa during 2002 decreased to levels lower than any year since the mid-1990s.) The largest proportion of foreign-born TB cases were young adults 25 to 44 years of age; the proportion of pediatric cases (less than 15 years of age) was higher among U.S.-born cases than among foreign-born cases (23% versus 8%), although all U.S.-born pediatric cases reported in 2002 occurred in house-holds with foreign-born parents or other family members. The proportion of cases among persons 65 years of age or older was higher among U.S.- born persons than among foreign-born persons (25% versus 7%). Among 173 foreign-born persons diagnosed with TB disease in Minne sota during 2002 and whose date of arrival in the U.S. was known, 31 (18%) were diagnosed within 12 months of arrival in the U.S., and an additional 84 (49%) were diagnosed 2 to 5 years after arriving in this country. All individuals who arrive in the U.S. as either immigrants or refugees receive a medical evaluation overseas to identify conditions (such as infectious pulmonary TB disease) of public health concern. In 2002, only two (7%) of 27 immigrants/refugees diagnosed in Minnesota with TB disease within 12 months of their arrival in the U.S. had any TB-related condition noted in the results of their pre-immigration medical exams. These findings highlight the need for clinicians not to rely exclusively on the overseas exam to identify TB disease among newly arrived foreign-born persons; providers should thoroughly pursue screening, evaluation, and, if indicated, treatment of active TB disease or latent TB infection among patients who originate from areas where TB is endemic. Other less frequent risk factors among TB cases in Minnesota included homelessness (6%), HIV infection (4%), incarceration in a correctional facility (1%), and residence in a nursing home (1%). The percentage of homeless TB case-patients in 2002 was the highest since 1995.
Twenty-five (29%) of the state's 87 counties reported at least one case of TB disease in 2002, with the majority (78%) of TB cases in the seven-county Twin Cities metropolitan area, particularly among residents of Hennepin (54%) and Ramsey (16%) Counties. However, the percentage of cases reported from Greater Minnesota (22%) increased in 2002, while the percentage of cases from Hennepin County decreased to the smallest proportion in more than 5 years.
Drug-resistant TB is a critical public health and clinical concern, both globally and locally. The prevalence of drug resistance among TB cases reported in Minnesota exceeds comparable figures nationally. In 2002, 52 (28%) cases of drug-resistant TB were reported in Minnesota among 187 culture-confirmed cases for whom drug susceptibility results were available, including 25 (13%) cases resistant to isoniazid and six (3%) cases of multidrug-resistant TB (MDRTB) (i.e., resistant to at least isoniazid and rifampin) (Table 5). This is the highest prevalence of MDR-TB statewide since such data have been reported and considerably higher than the prevalence of MDR-TB nationally (1.2%) in 2001. The prevalence of drug-resistance among foreign-born cases (31%) increased slightly. The prevalence of drug resistance among U.S.-born cases (15%) decreased from 2001 yet was comparable to recent years. Forty-six (88%) of the 52 persons with drug-resistant TB disease reported in 2002 were born outside the U.S., including 23 (88%) of 26 isoniazid- resistant cases and five (83%) of six MDR-TB cases. The one U.S.- born MDR-TB case was resistant to all five first-line TB medications. This case was the first U.S.-born MDR-TB case ever reported in Minnesota. However, this patient had resided outside the U.S. for many years.
More detailed TB surveillance data and other TB-related resources (including patient education materials translated in nine languages) are available on the MDH TB Program's web site.