While the number of tuberculosis (TB) cases reported nationally has been declining since 1993, the incidence and epidemiology of TB in Minnesota are following different trends. In 2000, 178 new cases of TB disease (3.6 per 100,000 population) were reported. This is the second largest number of cases reported in 20 years, after the 201 cases reported in 1999. For the fourth consecutive year, the incidence of TB disease in Minnesota remains at or above the national goal of 3.5 cases per 100,000 for the year 2000.
During 2000, 25 of the 87 counties in Minnesota reported at least one case of TB disease. However, the majority (76%) of TB cases occurred in the seven-county Twin Cities metropolitan area, particularly among residents of Hennepin (9.4 per 100,000) and Ramsey (4.7 per 100,000) Counties. Approximately 20% of cases occurred in greater Minnesota, with increasing incidence in specific areas.
The most significant factor in the epidemiology of TB in Minnesota is the large and increasing percentage of TB cases that occur among foreign-born persons (Figure 9). The percentage continued to increase in 2000, with 146 (82%) cases occurring in this population. This trend reflects the changing demographics of immigrant populations arriving in the state, particularly persons arriving from regions of the world where TB is prevalent. Among the 146 foreign-born persons diagnosed with TB disease in Minnesota during 2000, 41 (28%) were diagnosed within 12 months of arrival in the United States; an additional 30 (21%) were diagnosed 2 to 5 years after arriving in this country. The most common regions of origin for foreign-born persons with TB disease reported in 2000 included sub-Saharan Africa (58%), South/Southeast Asia (22%), and Latin American/Caribbean countries (18%) (Figure 10). More than half of foreign-born TB cases were 20 to 39 years of age, while the most common (28%) age group among U.S.-born cases was those 60 years of age or older. Foreign-born TB cases were more likely than those born in the U.S. to have extra-pulmonary sites of disease (42% vs. 33%, respectively). Other less frequent risk factors among TB cases in Minnesota included HIV infection (4%), homelessness (3%), incarceration in a correctional facility (2%), and residence in a nursing home (2%).
The increasing incidence of drug-resistant TB is a critical public health and clinical concern globally. In 2000, Minnesota reported 37 (26%) cases of drug-resistant TB among the 140 culture-confirmed cases for whom drug susceptibility results were available, including 23 (16%) cases resistant to isoniazid and one (1%) case of multi-drug resistant (MDR) disease resistant to isoniazid, rifampin, pyrazinamide, and streptomycin. Compared to data from the past 5 years, these figures represent an increase in both overall drug resistance and INH-resistance. However, the specific drug which showed the largest increase in resistance was streptomycin (17% of cases were resistant), which is the least commonly used of the five first-line anti-TB medications. Foreign-born TB patients in Minnesota are approximately three times more likely than those born in the U.S. to have drug-resistant disease (Table 6). Of 37 persons with drug-resistant TB disease reported in 2000, 34 (92%) were born outside the U.S., including the case of MDR-TB. These cases likely represented primary drug resistance acquired overseas rather than secondary resistance resulting from nonadherence to prescribed therapy. Current national guidelines recommend initial four-drug therapy for all TB cases in areas where the prevalence of INH resistance is 4% or greater. Twelve percent of all TB cases reported in Minnesota from 1996 to 2000 were resistant to at least INH; therefore, all TB cases in Minnesota initially should receive four-drug therapy until drug sensitivities are known.
More detailed TB surveillance data and other TB-related resources are available on the MDH TB web site.