While the number of cases of tuberculosis (TB) disease reported nationally has decreased each year since 1993, the incidence of TB in Minnesota increased throughout much of the 1990s and peaked at 239 TB cases (4.8 cases per 100,000 population) in2001. In 2004, 199 new cases of TB disease (3.9 cases per 100,000 population) were reported in Minnesota, representing a 7% decline from 2003 and the third consecutive year of decreasing incidence since 2001 (Figure 4). The incidence of TB disease in Minnesota, however, exceeds the U.S. Healthy People 2010 objective of 1.0 cases per 100,000 population.
In several ways, the epidemiology of TB in Minnesota is distinct from other states and has been a precursor of trends that now are emerging nationally. The most significant such factor is the very large proportion of TB cases reported among foreign-born persons in Minnesota, which has averaged 80% over the past 5 years. In 2004, 163 (82%) new TB cases in Minnesota occurred in persons born outside the United States. In contrast, 54% of TB cases reported nationwide in 2004 were foreign-born.
The 163 foreign-born TB case-patients reported in 2004 represent 33 different countries of birth. The most common region of birth among foreign-born TB cases reported in 2004 was sub-Saharan Africa (59%), followed by South/Southeast Asia (15%) and Latin America/Caribbean (15%) (Figure 5). The ethnic diversity among these foreign-born TB cases reflects the unique and constantly changing demographics of immigrant and other foreign-born populations arriving in Minnesota.
Persons 15 years of age or older who arrive in the United States as immigrants or refugees receive a medical evaluation overseas that includes screening for pulmonary TB disease. Among 161 foreign-born persons who were diagnosed with TB disease in Minnesota during 2004 and whose date of arrival in the United States was known, 96 (60%) were diagnosed less than 5 years after arriving in this country. Of 36 TB case-patients 15 years of age or older who were diagnosed within 12 months of their arrival in the United States and who arrived as immigrants or refugees, only six (17%) had any TB-related conditions noted in their pre-immigration medical exams performed overseas. These findings highlight the need for clinicians to have a high index of suspicion for TB among newly arrived foreign-born persons, regardless of the results of medical exams performed overseas. Health care providers should pursue thorough screening, evaluation, and, if indicated, treatment of active TB disease or latent TB infection among patients who originate from regions where TB is endemic.
Both demographic and clinical characteristics of TB cases reported in Minnesota differ between foreign-born and U.S.-born patients. For example, the majority (71%) of foreign-born TB case-patients reported in Minnesota in 2004 were 15 to 44 years of age, whereas the majority (58%) of U.S.-born TB cases occurred among persons 45 years of age or older. The proportions of pediatric cases (less than 15 years of age) and those 65 years of age or older were larger among U.S.-born TB cases than among foreign-born cases (22% versus 9% and 25% versus 9%, respectively). The relatively high proportion of U.S.-born pediatric cases can be attributed primarily to children born in the U.S. to foreign-born parents. Also, extrapulmonary TB disease is reported more frequently among foreign-born TB cases than among U.S.-born cases in Minnesota. In 2004, extrapulmonary TB was the most common (52%) form of TB disease among foreign-born TB cases, whereas 44% of U.S.-born TB cases had an extrapulmonary site of disease (Figure 6).
Aside from country of birth, other less common risk factors among TB cases reported in Minnesota during 2004 included HIV infection (7%), substance abuse (i.e., illicit drug use and/or alcohol abuse) (5%), homelessness (2%), and residence in a nursing home (1%). Notably, the prevalence of HIV infection among TB cases reported in 2004 was the highest since MDH began collecting this information in 1993. Ten (77%) of the 13 TB case-patients reported in 2004 with HIV co-infection were foreign-born persons, nine (90%) of whom were born in Africa. In 2004, no new TB cases were reported among inmates at correctional facilities in Minnesota.
Twenty-seven (31%) of the state’s 87 counties reported at least one case of TB disease in 2004, with the majority (79%) of cases occurring in the seven-county Twin Cities metropolitan area, particularly in Hennepin (52%) and Ramsey (14%) Counties, both of which have public TB clinics. Thirteen percent of TB cases occurred in the five suburban Twin Cities metropolitan counties (i.e., Anoka, Dakota, Carver, Scott, and Washington). Olmsted County, which maintains a public TB clinic staffed jointly by the Olmsted County Health Department and Mayo Clinic, represented 7% of TB cases reported statewide in 2004. The remaining 15% of cases occurred in primarily rural areas of Greater Minnesota.
Drug-resistant TB is a critical and growing concern in the prevention and control of TB in Minnesota, as well as nationally and globally. The prevalence of drug-resistant TB in Minnesota, particularly resistance to isoniazid (INH) and multi-drug resistance, exceeds comparable national figures. In 2004, 22 (16%) of 138 culture-confirmed TB cases with drug susceptibility results available were resistant to at least one first-line anti-TB drug (i.e., INH, rifampin, pyrazinamide, or ethambutol). In particular, 17 (12%) cases were resistant to INH, and five (4%) cases were multidrug-resistant (i.e., resistant to at least INH and rifampin). As of 2004, MDH updated its definition of first-line TB drug resistance to exclude streptomycin resistance, in accordance with recently revised national recommendations for the treatment of TB disease, which no longer include streptomycin as a first-line anti-TB drug. Drug resistance is significantly more common among foreign-born TB cases in Minnesota than among U.S.-born cases. The prevalence of drug-resistance among foreign-born TB cases reported in 2004 was 18%, compared to 5% among U.S.-born cases. Of particular concern, eight (38%) of 21 multidrug-resistant TB (MDR-TB) cases reported during the past 5 years (2000-2004) were resistant to all four first-line drugs. These eight pan-resistant MDR-TB case-patients represented seven different countries of birth (i.e., one each from Ethiopia, Laos, Moldova, Somalia, South Korea, Thailand, and two from the U.S.). One of the two U.S.-born pan-resistant patients had resided in Africa for several years; the other was a young child infected by a foreign-born family member.
The epidemiology of TB in Minnesota highlights the need to support global TB elimination strategies, as well as local TB prevention and control activities targeted to foreign-born persons. MDH is among 22 sites funded by the CDC to conduct a study designed to identify missed opportunities for preventing TB disease among foreign-born populations in the United States and Canada. This study, which includes conducting more than 50 1hour interviews with foreign-born TB case-patients diagnosed in Minnesota, began in the summer of 2004 and will continue throughout 2005.
TB-related resources for patients and health care providers (including patient education materials translated in nine languages) are available on the MDH Tuberculosis (TB) Programís web site.
Note: For up to date information on Tuberculosis see Tuberculosis (TB)
Go to full issue: DCN, July/August 2005: Volume 33, Number 4