A workplace tuberculosis case investigation in the presence of immigrant contacts from high prevalence countries

The highest prevalence of tuberculosis (TB) occurs in foreign born immigrants in the United States. Contact investigations at work sites with mostly immigrant workers present multiple practical problems. Recently 402 contacts were investigated at a meat packing plant in rural Texas by the Texas Department of State Health Services (DSHS). Our objective was to study the approach and effectiveness of this intensive investigation. We reviewed information, including symptoms, BCG status, TB history, X-rays, and treatment, on the sentinel case and 47 contacts managed by the Texas DSHS TB Division in Lubbock, TX. We used a gamma interferon release assay (T-SPOT.TB) to identify contacts with TB infection. The sentinel case was foreign born and had cavitary TB with acid-fast positive smears. Forty-two work site contacts were foreign born, and five were US born. The foreign born contacts were from Sudan, Somalia, Mexico, Burma, and Haiti; 18 contacts had a history of BCG vaccination. T-SPOT.TB tests were positive in 20 contacts, borderline in four, and negative in 23. Contacts with borderline results had negative repeat tests. Twenty-three contacts with negative T-SPOT.TB tests were scheduled for repeat tests in 4 weeks, but only four returned for this testing. Chest X-rays were abnormal in two contacts who were started on treatment. Sputum was collected in three individuals; one was culture positive for pan-sensitive Mycobacterium tuberculosis. Twelve contacts were treated for latent TB. Our investigation established an infection rate of 42.5% in this work site contact cohort, which is similar to the 39% prevalence reported by the Center for Disease Control. The use of T-SPOT.TB assays simplified testing in immigrants with high rates of BCG vaccination. Our investigation was complicated by language barriers, varying and uncertain levels of exposure, and a high rate of drop outs in the negative T-SPOT.TB contacts. This concerted effort provides a model for investigating work site contacts, especially with numerous immigrants, and illustrates the problems associated with these investigations.