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US M. bovis rates remain stable between 2006-2013
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The annual percentage of tuberculosis cases attributable to Mycobacterium bovis has remained stable in the United States and primarily affected children, Hispanic or foreign-born citizens, and those who reside in states near the Mexican border, according to a recently published analysis.
“Mycobacterium bovis is one of several mycobacteria of the Mycobacterium tuberculosis complex that are closely related and pathogenic,” Colleen Scott, DrPH, MPH, epidemic intelligence service officer at the CDC, and colleagues wrote. “Because M. bovis and M. tuberculosis disease are clinically indistinguishable, genotyping can be used to help differentiate between the two causative agents. Determining this distinction is epidemiologically valuable for TB control because disease caused by M. bovis may require distinct interventions to interrupt transmission.”
Scott and colleagues examined TB cases reported through the National Tuberculosis Genotyping Service (NTGS) from 2008 to 2013. They included all cases with genotyping data indicating either M bovis or M. tuberculosis infection, and excluded those with M. tuberculosis complex isolates with other Mycobacteria species. From these, the researchers calculated the annual proportion of TB cases resulting from M. bovis, and identified characteristics independently associated with the infection.
There were 862 M. bovis and 58,411 M. tuberculosis cases with appropriate culture and genotyping data included in the study. The national proportion of TB cases caused by M. bovis was similar each year (range, 1.3% to 1.6%), and 93.6% of cases were among Hispanics. Of these, 74.1% were born in Mexico, although annual incidence among this group declined over the study period.
In multivariate analysis comparing cases among U.S.-born cases, females, Hispanics, children aged 14 years or younger, patients with any extrapulmonary disease and patients living in U.S.-Mexican border counties were associated with increased M. bovis prevalence. Analyses among foreign-born cases indicated similar trends.
The findings are in line with surveillance data from previous years, the researchers wrote, and could help guide interventions targeting these highly effected groups.
“Interagency and cross-border collaborations can enhance and optimize the effectiveness of current importation laws regarding unpasteurized milk products entering the United States,” they wrote. “While M. bovis is predominately characterized by an extrapulmonary clinical presentation, our finding that one-third of all cases in the United States present with exclusively pulmonary disease demonstrates the need for more research on airborne transmission of M. bovis, especially regarding its relative infectiousness compared to M. tuberculosis.” – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures.
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