Mini epidemic of isoniazide resistant TB in rural TN: a need for supervised preventive therapy

With the resurgence of tuberculosis (TB) in the late 1980s, multi-drug-resistant TB (MDR-TB) also became a serious challenge to the TB control programs across the United States (US). While the incidence of TB resumed a downward trend in the mid 1900s, drug-resistant TB continues to be a national and international problem. We reviewed the public health data of drug-resistant TB cases (1996-2002) in Greene County, TN, with a detailed analysis of their contact investigation. Our study included demographic data of age, sex, race, human immunodeficiency virus (HIV) status and other known risk factors for drug-resistant TB. Contact investigation of two patients with isoniazide-resistant active pulmonary TB led to the discovery of two additional cases of active pulmonary tuberculosis, one of them being a 14-month-old child. All four of the patients were U.S. born, had negative HIV tests, and lacked other risk factors for drug-resistant TB. In all four cases, the Mycobacterium tuberculosis isolates were resistant to isoniazide, three were streptomycin resistant, and was ethambutol resistant. A total of 65 close contacts were identified, 11 of whom had a positive purified protein derivative (PPD) skin test indicating latent TB infection. Based on the American Thoracic Society's recommendations, the contacts with a positive PPD were prescribed rifampin for chemo-prevention rather than INH. However, one active case was detected from this infected contact who had failed to comply with chemo-preventive therapy. The second active case was a child who developed active pulmonary TB before chemoprevention could be initiated. Drug culture profile and DNA analysis (RFLP) confirmed the same source for TB transmission. The 11/65 (16.5 percent) infection rate among the contact was comparable to the state average (p < 0.05), but the case rate of 4/65 (6.15 percent) was high. In two out of four active cases, who were family members of the known cases, active infection could have been prevented. High prevalence of drug-resistant TB in rural areas without any known risk factors and failure of prevention are crucial findings of our study. Clinicians practicing in a rural setting should be aware of occasional mini-outbreaks of drug-resistant TB. Supervised therapy for rifampin chemo-prophylaxis and other standard public health measures successfully controlled this mini-epidemic. Awareness of drug resistance in family clusters and an urgent need for prompt chemo-preventive measures are important in implementing successful TB control programs.