Elsevier

Annals of Epidemiology

Volume 27, Issue 6, June 2017, Pages 371-376.e5
Annals of Epidemiology

Original article
Individual- and neighborhood-level contextual factors are associated with Mycobacterium tuberculosis transmission: genotypic clustering of cases in Michigan, 2004–2012

https://doi.org/10.1016/j.annepidem.2017.05.009Get rights and content

Abstract

Purpose

Using genotyping data of Mycobacterium tuberculosis isolates from new cases reported to the tuberculosis (TB) surveillance program, we evaluated risk factors for recent TB transmission at both the individual- and neighborhood- levels among U.S.-born and foreign-born populations.

Methods

TB cases (N = 1236) reported in Michigan during 2004 to 2012 were analyzed using multivariable Poisson regression models to examine risk factors for recent transmission cross-sectionally for U.S.-born and foreign-born populations separately. Recent transmission was defined based on spoligotype and 12-locus-mycobacterial interspersed repetitive unit–variable number tandem repeat typing matches of bacteria from cases that were diagnosed within 1 year of each other. Four classes of predictor variables were examined: demographic factors, known TB risk factors, clinical characteristics, and neighborhood-level factors.

Results

Overall, 22% of the foreign-born cases resulted from recent transmission. Among the foreign-born, race and being a contact of an infectious TB case were significant predictors of recent transmission. More than half (52%) of U.S.-born cases resulted from recent transmission. Among the U.S.-born, recent transmission was predicted by both individual- and neighborhood-level sociodemographic characteristics.

Conclusions

Interventions aimed at reducing TB incidence among foreign-born should focus on reducing reactivation of latent infection. However, reducing TB incidence among the U.S.-born will require decreasing transmission among socially disadvantaged groups at the individual- and neighborhood- levels. This report fills an important knowledge gap regarding the contemporary social context of TB in the United States, thereby providing a foundation for future studies of public health policies that can lead to the development of more targeted, effective TB control.

Introduction

Although the overall incidence of tuberculosis (TB) has been declining in the United States, stark disparities persist in the distribution of disease, particularly by race and nativity. Asian and Pacific Islanders (AI/PI) continue to have the highest incidence of TB in the United States and show no evidence of closing the gap with whites, whose incidence is lowest [1], [2]. Moreover, the rate of decline in TB incidence has recently begun to stagnate [3], particularly among foreign-born populations [4], and in both urban and rural populations [5], [6].

From a clinical perspective, measures of individual immune status and infectiousness are key to predicting transmission of Mycobacterium tuberculosis (MTB) [7]: individuals with underlying comorbidities, those with a positive sputum-smear, and those with abnormal chest radiography results are more likely to be associated with recent transmission. However, previous studies have also found both individual-level and neighborhood-level sociodemographic factors to be predictors of recent TB transmission. Individual-level sociodemographic characteristics such as younger age [8], [9], [10], minority race/ethnicity status [8], [11], male sex [9], [10], and being native-born [8], [11], [12], [13] have been associated with recent TB transmission. In addition, “known TB risk factors” as defined by the Centers for Disease Control and Prevention (CDC) surveillance forms [14], such as homelessness [8], [9], [13], incarceration [8], and drug use [13] have also been linked to recent transmission. Neighborhood-level studies have demonstrated that area-based measures of disadvantage are associated with increased incidence and transmission of TB, a finding particularly pronounced for those who are U.S.-born [15]. Several studies have also suggested the predictors of recent transmission are different for foreign-born and U.S.-born populations [16], highlighting the importance of investigating these two groups separately.

In 2012, Michigan had an annual incidence rate of 1.28 TB cases per 100,000 [17], notably lower than the U.S. national average incidence of 3.2 per 100,000 [4]. Despite Michigan's lower incidence, there is evidence of persistent disparities in TB risk, particularly by race and nativity [17]. Using TB surveillance data collected by the Michigan Department of Health and Human Services (MDHHS), we evaluated risk factors for recent transmission at both the individual- and neighborhood-levels among U.S.-born and foreign-born populations separately.

Section snippets

Study population and data collection

Our study subsample included only those cases with complete genotype data, both spacer oligonucleotide (spoligotype) and 12-locus-mycobacterial interspersed repetitive unit–variable number tandem repeat typing (MIRU-VNTR) results, and address information. The genotyping data are part of the CDC-based National Tuberculosis Genotyping Service [18]. Cases were excluded if they had incomplete genotyping data and/or were missing address information. The state of Michigan employs universal genotyping

Characteristics of the study population

A total of 1800 cases of TB were reported in Michigan from January 1, 2004 to December 31, 2012 (Supplementary Fig. 1). The final study sample consisted of 1236 cases, representing 69% of the 1800 total cases reported by MDHHS during this time period (Table 1). The racial/ethnic composition of these cases was 23% non-Hispanic white, 40% non-Hispanic black/African American, 25% Asian, 10% Hispanic, and 2% other. Most cases (72%) were between the ages of 18 and 64 years. The gender distribution

Discussion

We evaluated risk factors for recent transmission at both the individual and neighborhood levels among U.S.-born and foreign-born populations separately using a combination of genotyping and surveillance data from 1236 new TB cases reported in Michigan during 2004 through 2012.

Using time-restricted genotypic clusters as the proxy for recent transmission, we found significant differences between the U.S.-born and the foreign-born in the proportion of cases attributable to recent transmission.

Conclusions

Our findings point to the need for considering socioeconomic context in designing interventions aimed at reducing MTB transmission. Although a focus on individual-level factors in TB control may have reduced overall TB incidence in the United States during the last decades, our results suggest that this is insufficient to address enduring disparities in TB incidence that are largely patterned by social and economic disadvantages. Reducing disparities in TB incidence will require strategies that

Acknowledgments

The authors thank their collaborators at the TB Control Program at the Michigan Department of Health and Human Services for their contribution to the collection of the data used for this study. Dr. Noppert received partial support from the University of Michigan Rackham Graduate School and NIA grant 5 T32-AG000029-40.

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    1

    Present affiliation: Center for the Study of Aging and Human Development, Duke University, 201 Trent Dr. Durham, NC 27710; email: [email protected].

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