Academic journal article Bulletin of the World Health Organization

Cross-Sectional Assessment Reveals High Diabetes Prevalence among Newly-Diagnosed Tuberculosis cases/Une Evaluation Transversale Revele Une Prevalence De Diabete Elevee Dans Les Cas De Diabete Nouvellement diagnostiques/La Evaluacion De Una Muestra Aleatoria Y Representativa Revela Una Elevada Prevalencia De la Diabetes Entre Los Casos De Tuberculosis Recien Diagnosticados

Academic journal article Bulletin of the World Health Organization

Cross-Sectional Assessment Reveals High Diabetes Prevalence among Newly-Diagnosed Tuberculosis cases/Une Evaluation Transversale Revele Une Prevalence De Diabete Elevee Dans Les Cas De Diabete Nouvellement diagnostiques/La Evaluacion De Una Muestra Aleatoria Y Representativa Revela Una Elevada Prevalencia De la Diabetes Entre Los Casos De Tuberculosis Recien Diagnosticados

Article excerpt

Introduction

Tuberculosis (TB) continues to be the leading killer among bacterial diseases worldwide. In 2009, more than 9 million new cases were diagnosed and 1.7 million people died from the disease. (1) The World Health Organization (WHO) suspects that TB control is being undermined by the growing number of patients with diabetes mellitus in the world, which currently stands at an estimated 285 million but is anticipated to reach 438 million by 2030. (2,3) Prior to the 1950s reports of an association between diabetes (primarily type 1) and TB were frequent in the literature, but they waned as insulin and drugs against TB became available. (4,5) This association (now with type 2 diabetes) was rccognized again in the 1990s (6-9) and is currently supported by a growing body of literature. (6-17) According to a recent meta-analysis, diabetes patients have three times the risk of contracting TB as non-diabetics (95% confidence interval, CI: 2.3-4.3) (18) and studies report the fraction of TB cases attributable to diabetes to be between 15% and 25%. (9,13,16) The biological basis for the association between both diseases is not fully understood but studies suggest that diabetes depresses the immune response, which in turn facilitates infection with Mycobacterium tuberculosis and/or progression to symptomatic disease. This is corroborated by the fact that diabetes is generally diagnosed before TB develops. (4,19-22)

Despite the suggested importance of diabetes as a risk factor for TB, most contemporary studies ate based on secondary data or self-reported diabetes status. (6-17) The contribution of diabetes to the burden of TB may be more conspicuous in countries where both diseases are highly prevalent: Bangladesh, Brazil, China, India, Indonesia, Pakistan, and the Russian Federation ate high-burden countries and rank among the 10 countries with the highest numbers of diabetes patients (2,23) and also classified as high-burden for TB. However, the risk of TB attributable to diabetes has only been reported for India and it was estimated from secondary data. (13) We need to gain a deeper understanding of the differences between TB patients with and without diabetes to assist in the development of guidelines to prevent co-morbidity.

Our research team is strategically located on the Texas-Mexico border, where TB is endemic. In 2007 the overall incidence of TB was 10.5 cases per 100 000 in south Texas and 38 per 100 000 in north-eastern Mexico (personal communications, JL Robles, Secretaria de Salud de Tamaulipas [SSA-Tamaulipas]; Brian Smith and Nita Ngo, Texas Department of State and Health Services [DSHS]). Diabetes prevalence among adults over the age of 20 years is 19.4% in South Texas and 15.1% in northeastern Mexico. (24,25) Our previous studies were conducted with data extracted from existing surveillance databases for TB control and were based on self-reported diabetes. (17) In this study our objective was to estimate the risk of TB attributable to diabetes in this population along the Mexican border using primary data from patients newly diagnosed with TB and tested for diabetes.

Methods

Patient enrolment

Referral patients with probable TB were enrolled between March 2006 and September 2008 at the TB clinics in Hidalgo and Cameron County Health Departments, which are the TB reference centres for South Texas counties (South Texas), and the SSA-Tamaulipas in Matamoros, Mexico (north-eastern Mexico). Jail inmates and individuals < 20 years of age were excluded. Individuals fulfilling the inclusion criteria but refusing to participate (n = 80; 95% from South Texas) did not differ with respect to age, gender, race or ethnicity from those enrolled (data not shown). Participants signed informed consent. The study was approved by the institutional review boards of the participating institutions in Mexico and the United States.

For TB diagnosis we used standard WHO definitions: culture positive for Mycobacterium tuberculosis (confirmed case), sputum smear positive for acid-fast bacilli when culture data were not available (smear-positive case), of clinical diagnosis only when microbiological test results were negative or not available (clinical case: symptoms compatible with TB and documentation of anti-TB treatment for at least 6 months). …

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