American Journal of Epidemiology Advance Access published online on July 11, 2007
American Journal of Epidemiology, doi:10.1093/aje/kwm135
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PRACTICE OF EPIDEMIOLOGY |
What's Driving the Decline in Tuberculosis in Arkansas? A Molecular Epidemiologic Analysis of Tuberculosis Trends in a Rural, Low-Incidence Population, 1997–2003
1 Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, MI
2 Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR
3 Central Arkansas Veterans' Healthcare Center, Little Rock, AR
4 Departments of Internal Medicine and Microbiology, College of Public Health, University of Arkansas for Medical Sciences, Little Rock, AR
5 Division of Health, Arkansas Department of Health and Human Services, Little Rock, AR
Correspondence to Dr. Zhenhua Yang, Department of Epidemiology, School of Public Health, University of Michigan, 109 Observatory Street, Room 3542, Ann Arbor, MI 48109-2029 (e-mail: zhenhua{at}umich.edu).
Received for publication November 9, 2006. Accepted for publication March 19, 2007.
Incident cases of tuberculosis may result from a recently acquired Mycobacterium tuberculosis infection or from the reactivation of a latent infection acquired in the remote past. The authors used molecular fingerprinting data to estimate the relative contributions of recent and remotely acquired infection to the yearly incidence of tuberculosis in Arkansas, a state with a largely rural population where the incidence of tuberculosis declined from 7.9 cases per 100,000 population to 4.7 cases per 100,000 between 1997 and 2003. The authors used a time-restricted definition of clustering in addition to the standard definition in order to increase the specificity of the clustering measure for recent transmission. The greatest overall declines were seen in non-Hispanic Blacks (from 13.8 cases per 100,000 in 1997 to 6.5 cases per 100,000 in 2003) and persons aged 65 years or more (from 19.9 cases per 100,000 in 1997 to 8.5 cases per 100,000 in 2003). In both groups, the incidence of nonclustered cases declined more dramatically than the incidence of clustered cases. This suggests that the decline in rates resulted primarily from declining rates of disease due to reactivation of past infections. Declines in the overall incidence of tuberculosis in a population may not necessarily result from declines in active transmission.
Arkansas; cohort effect; DNA fingerprinting; epidemiology, molecular; infection control; Mycobacterium tuberculosis; rural health; tuberculosis
Abbreviations: MSA, Metropolitan Statistical Area; RFLP, restriction fragment length polymorphism; TB, tuberculosis
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