摘要：Objectives. We sought to compare prevalence and determinants of multidrug-resistant tuberculosis (MDR-TB) between tuberculosis patients in Baja California, Mexico, and Hispanic patients in California. Methods. Using data from Mexico’s National TB Drug Resistance Survey (2008–2009) and California Department of Public Health TB case registry (2004–2009), we assessed differences in MDR-TB prevalence comparing (1) Mexicans in Baja California, (2) Mexico-born Hispanics in California, (3) US-born Hispanics in California, and (4) California Hispanics born elsewhere. Results. MDR-TB prevalence was 2.1% in Baja California patients, 1.6% in Mexico-born California patients, 0.4% in US-born California patients, and 2.7% in Hispanic California patients born elsewhere. In multivariate analysis, previous antituberculosis treatment was associated with MDR-TB (odds ratio [OR] = 6.57; 95% confidence interval [CI] = 3.34, 12.96); Mexico-born TB patients in California (OR = 5.08; 95% CI = 1.19, 21.75) and those born elsewhere (OR = 7.69; 95% CI = 1.71, 34.67) had greater odds of MDR-TB compared with US-born patients (reference category). Conclusions. Hispanic patients born outside the US or Mexico were more likely to have MDR-TB than were those born within these countries. Possible explanations include different levels of exposure to resistant strains and inadequate treatment. Tuberculosis (TB) is an important health concern along the 1950-mile international border shared by Mexico and the United States. The neighboring states of Baja California, Mexico, and California, United States, have TB incidence rates that far exceed those of their respective countries. In 2008, the incidence rate for TB in Baja California was 50.9 per 100 000, versus 17.1 per 100 000 nationally in Mexico. 1 In California, the incidence of TB that same year was 7.4 per 100 000, compared with 4.2 cases per 100 000 persons in the United States. 2 Multidrug-resistant tuberculosis (MDR-TB) is TB disease associated with Mycobacterium tuberculosis strains that are resistant to isoniazid and rifampin, the 2 most effective TB medications available. 3 MDR-TB is found in Mexico and California, and significantly increases treatment and societal costs of TB, with case fatality rates ranging from 12% in HIV-negative to 90% in HIV coinfected persons. 3 Although TB control efforts worldwide are starting to decrease TB incidence and mortality, 4,5 the emergence of MDR-TB is “threatening to destabilize global TB control,” 6 (p261) and could rapidly turn TB into an untreatable disease, even in high-income countries. 7 California had an average of 41 MDR-TB cases per year from 1994 to 2003—the highest incidence of MDR-TB in the United States. 8 More than 85% of the incident MDR-TB cases in California from 1993 to 2006 were among foreign-born individuals, 28% of whom were born in Mexico. 7 In Mexico, although some studies of MDR-TB prevalence in specific populations have been conducted, 9–12 there is no routine surveillance data on MDR-TB for comparison. California and Baja California share a strong migratory dynamic. Translocation and contact between inhabitants of both sides of the border are frequent, and familial and other social relations extend across the border. 13 This condition affects the binational epidemiology of TB and MDR-TB, which is heavily influenced by social networks. 14 The regular contact between residents of Baja California and California involves people of all ethnicities and social groups, but it is most intense for those identified as “Hispanics,” a group that, in California, is composed mainly of persons of Mexican origin. Susceptibility testing is not routinely conducted in all TB cases in Mexico. However, from 2008 through 2009, as part of a national survey, all newly diagnosed TB cases were tested for drug resistance. 15 Taking advantage of this, we studied differences in the prevalence and determinants of newly diagnosed MDR-TB cases among TB patients in Baja California as compared with Hispanics (a proxy for patients with ties to Mexico) in California, from 2004 through 2009. Although the concepts of ethnicity and race can be questioned when they imply that real genetic differences exist between different human groups, 16 and the label “Hispanic” has been criticized for its lack of specificity, 16,17 in the absence of other information, self-reported ethnicity can be used as an indicator of certain social and cultural characteristics. 16 It can also be an index for social inequalities, including discrimination, that reflect inequalities in health. 18 In the study of TB transmission between contiguous states on either side of the US–Mexico border, self-identified ethnicity can be used in this way as a proxy for people who might share social networks, related TB strains, and some social conditions. The TB control programs of Baja California and California are different in terms of resources, mainly in terms of capacity for bacterial culture and sufficiency of staff. Also, completion of treatment is mandated by law in California, which should make it less likely for recently diagnosed cases to have a history of previous treatment. 19,20 The objective of this study was to compare the prevalence of risk factors for MDR-TB, including previous treatment and country of birth, among newly diagnosed TB cases (both previously treated and never treated) in Baja California, with those among Hispanics living in California. Recognizing the differences in resources between California and Baja California health systems, we hypothesized that (1) the overall prevalence of MDR-TB would be higher in Baja California than in California, (2) the proportion of TB cases with previous treatment would be higher in Baja California than in California, and (3) the prevalence of MDR-TB would be the same in Baja California and California after adjusting for previous antituberculosis treatment, one of the strongest predictors for MDR-TB globally.
