Tuberculosis, 2013

In 2013, 151 cases of active tuberculosis (TB) disease (2.8 cases per 100,000 population) were reported. This represents a 7% decrease in both the number of cases (162) and the incidence rate (3.0) compared to 2012, as well as a 37% decrease in the number of cases since 2007, when the highest number (238 cases) in the past decade was reported. As seen in most years, Minnesota’s TB incidence rate in 2013 was below the national rate of 3.0 cases per 100,000 population. Two (1%) of the cases died due to TB or TB-related causes.

Twenty-one (24%) of the state’s 87 counties reported at least 1 new TB case in 2013. The majority (73%) of cases occurred in the metropolitan area, primarily in Hennepin (34%) and Ramsey (26%) Counties. Thirteen percent of cases in 2013 were reported in the other five metropolitan counties (i.e., Anoka, Carver, Dakota, Scott, and Washington). The remaining 27% of cases were reported from outside the metropolitan area, which is higher than in previous years. Among metropolitan area counties, the highest TB incidence rate in 2013 was reported in Ramsey County (7.5 cases per 100,000 population), followed by Hennepin County (4.3 cases per 100,000), and Anoka County (2.4 cases per 100,000 population). The TB incidence rate for all Greater Minnesota counties combined was 1.7 per 100,000 population.

The majority (82%) of cases in 2013 were identified as a result of individuals seeking medical care due to symptoms of TB disease. Various targeted public health interventions identified a portion of the remaining cases. Such methods of case identification are considered high priority, core TB prevention and control activities; they include TB contact investigations (3%), domestic refugee health assessments (1%), and follow-up evaluations resulting from abnormal findings on pre-immigration exams performed overseas (1%). An additional 10% were identified through a variety of other means (e.g., occupational screening). Four (3%) cases were diagnosed with active TB disease while being evaluated for another medical condition.

The incidence of TB disease is disproportionately high in racial minorities in the United States and in Minnesota. In 2013, 16 TB cases occurred among non-Hispanic whites (incidence rate: 0.4/100,000 population). In contrast, 60 cases occurred among blacks (incidence rate: 18.1/100,000), 55 among Asians (incidence rate: 21.9/100,000), and 4 among American Indians (incidence rate: 5.0/100,000). The vast majority of black cases (95%) and Asian cases (95%) reported in Minnesota in 2013 were foreign-born.

The most distinguishing characteristic of TB disease in Minnesota continues to be the large proportion of cases occurring among persons born outside the United States. Eighty-one percent of cases reported in 2013 occurred among foreign-born persons. In contrast, 65% of TB cases reported nationally in 2013 were foreign-born. The 123 foreign-born TB cases reported in Minnesota represented 23 different countries of birth; the most common region of birth among these patients was sub-Saharan Africa (47% of foreign-born cases), followed by South/Southeast Asia (36%), and Latin America (including the Caribbean) (10%) (Figure 7). All 6 U.S.-born pediatric (<15 years of age) cases had at least one foreign-born parent. The ethnic diversity among foreign-born TB cases in Minnesota reflects the unique and constantly changing demographics of immigrants and other foreign-born populations arriving in the state.

Among the foreign-born TB cases reported during 2013, 14% were diagnosed within the first 12 months after arriving in the United States, and an additional 14% were diagnosed 1 to 2 years after their arrival. These cases most likely acquired TB infection prior to immigrating and started progressing to active TB disease shortly after arrival. Of the 11 TB cases ≥15 years of age who arrived as immigrants or refugees and diagnosed in Minnesota within 12 months of arriving in the United States, only 2 had any TB-related condition noted in their pre-immigration medical examination reports. 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.

Fifty-eight percent of Minnesota cases reported had TB disease exclusively in the lungs, or pulmonary TB. Another 7% had both pulmonary and extrapulmonary sites of disease. Almost half (46%) of foreign-born and 29% of U.S.-born TB cases had at least one extrapulmonary site of disease (including those who also had pulmonary disease). Among cases with an extrapulmonary site of disease, the most common sites were lymphatic (45%), followed by bone/joint (23%), and pleural (9%).

Aside from foreign-born persons, individuals in other high risk groups comprise a smaller proportion of the cases in Minnesota. Among cases reported in 2013, 23% occurred among persons with certain medical conditions (excluding HIV infection) that increase the risk for progression from latent TB infection (LTBI) to active TB disease (e.g., diabetes, prolonged corticosteroid or other immunosuppressive therapy, end stage renal disease). Following the presence of these underlying medical conditions, the next most common risk factor was substance abuse (including alcohol abuse and/or injection and non-injection drug use), with 6% of TB cases reported in 2013 having a history of substance abuse during the 12 months prior to their TB diagnosis. Four (3%) were co-infected with HIV. The percentage of new TB cases with HIV co-infection in Minnesota remains lower than that reported nationally (7%). Other high risk groups accounting for the remainder of cases reported in Minnesota included homeless persons (3%) and residents of long-term care facilities (1%).

In 2013, of 113 culture-confirmed TB cases with drug susceptibility results available, 24 (21%) were resistant to at least one first-line anti-TB drug (i.e., isoniazid (INH), rifampin, pyrazinamide, or ethambutol), including 13 (12%) cases resistant to INH. There were no cases of multidrug-resistant TB (MDR-TB, or resistance to at least INH and rifampin) reported in 2013. In comparison, 19% of culture-confirmed cases in 2012 with susceptibility results available were resistant to at least one first-line anti-TB drug, 10% were resistant to INH, and 1 (0.8%) had MDR-TB.

• For up to date information see>> Tuberculosis (TB)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2013