The ability of current overseas screening to detect tuberculosis among immigrants with abnormal chest radiographs is low. Improved diagnostic methods, enhanced screening measures, and postmigration follow-up are essential to control tuberculosis among immigrants and support US and global tuberculosis elimination.

RationaleEach year 1 million persons acquire permanent U.S. residency visas after tuberculosis (TB) screening. Most applicants undergo a 2-stage screening with tuberculin skin test (TST) followed by CXR only if TST-positive at > 5 mm. Due to cross reaction with bacillus Calmette-Guérin (BCG), TST may yield false positive results in BCG-vaccinated persons. Interferon gamma release assays exclude antigens found in BCG. In Vietnam, like most high TB-prevalence countries, there is universal BCG vaccination at birth. Objectives1. Compare the sensitivity of QuantiFERON ®-TB Gold In-Tube Assay (QFT) and TST for culture-positive pulmonary TB. 2. Compare the age-specific and overall prevalence of positive TST and QFT among applicants with normal and abnormal CXR.MethodsWe obtained TST and QFT results on 996 applicants with abnormal CXR, of whom 132 had TB, and 479 with normal CXR. ResultsThe sensitivity for tuberculosis was 86.4% for QFT; 89.4%, 81.1%, and 52.3% for TST at 5, 10, and 15 mm. The estimated prevalence of positive results at age 15–19 years was 22% and 42% for QFT and TST at 10 mm, respectively. The prevalence increased thereafter by 0.7% year of age for TST and 2.1% for QFT, the latter being more consistent with the increase in TB among applicants.ConclusionsDuring 2-stage screening, QFT is as sensitive as TST in detecting TB with fewer requiring CXR and being diagnosed with LTBI. These data support the use of QFT over TST in this population.

The goal of this study was to evaluate the effect of the specimen-processing method that uses the detergent C 18 -carboxypropylbetaine (CB-18) on the sensitivity of acid-fast bacillus (AFB) staining. Vietnamese immigrants with abnormal chest radiographs provided up to three sputum specimens, which were examined for acid-fast bacilli by use of direct auramine and Ziehl-Neelsen staining. The remaining sputum was split; half was cultured, and the other half was incubated with CB-18 for 24 h, centrifuged, and examined for AFB by both staining methods. CB-18 processing improved the sensitivity of AFB staining by 20 to 30% (only differences in auramine sensitivity were statistically significant) but reduced specificity by Ϸ20% (P < 0.05). These findings have direct utility for overseas migrant tuberculosis screening programs, for which maximizing test sensitivity is a major objective.Sputum smear microscopy to detect acid-fast bacilli (AFB) is a rapid, inexpensive, and highly specific tool for identifying persons with active tuberculosis (TB) and represents a critical component of overseas screening for immigrants. The sensitivity of the AFB smear method is moderate (1, 2, 8, 10); a recent study of overseas TB screening for United States immigrant visa applicants reported the sensitivity of AFB smears to be approximately 34% (9). The goal of this study was to evaluate the effects of C 18 -carboxypropylbetaine (CB-18) (10, 16) specimen processing on AFB smear sensitivity and specificity for detecting TB disease (i.e., Mycobacterium tuberculosis complex [MTBC] culture-positive TB disease) among United Statesbound immigrants from Vietnam.A prospective cohort of United States-bound adult (Ն18 years) Vietnamese immigrants with abnormal chest X rays (CXRs) suggestive of TB was enrolled at Cho Ray Hospital in Ho Chi Minh City, Vietnam, between May 2000 and June 2001. Applicants with CXR findings suggestive of TB disease provided up to three sputum specimens (5); only specimens of 10 ml or greater were eligible for analysis.Specimens were examined by direct staining by use of both auramine and Ziehl-Neelsen (ZN) staining techniques according to recommended procedures (7). After staining, equal volumes of 50 mM NaOH containing 0.5% N-acetyl-L-cysteine (NALC) were used to homogenize the specimens, and specimens were split approximately equally. One half of each specimen was transferred to the Institute Pasteur in Ho Chi Minh City, where culture facilities are available, and was digested by using the standard oxalic acid (OxAC) procedure (7). After centrifugation at 3,046 ϫ g for 15 min, specimens were decanted and the residue neutralized by using 4% NaOH containing phenol red. Portions of each specimen were analyzed by culture (BACTEC 12B with PANTA Plus [Becton Dickinson, Sparks, MD] and Lowenstein-Jensen slants).Positive 12B bottles underwent ZN staining to confirm the presence of AFB. Lowenstein-Jensen slants were incubated at 35°C to 37°C for two months and inspected weekly for growth. Tubes were examined macroscopically; o...

Objective. Use of tuberculin skin tests (TSTs) and interferon gamma release assays (IGRAs) as part of tuberculosis (TB) screening among immigrants from high TB-burden countries has not been fully evaluated. Methods. Prevalence of Mycobacterium tuberculosis infection (MTBI) based on TST, or the QuantiFERON-TB Gold test (QFT-G), was determined among immigrant applicants in Vietnam bound for the United States (US); factors associated with test results and discordance were assessed; predictive values of TST and QFT-G for identifying chest radiographs (CXRs) consistent with TB were calculated. Results. Of 1,246 immigrant visa applicants studied, 57.9% were TST positive, 28.3% were QFT-G positive, and test agreement was 59.4%. Increasing age was associated with positive TST results, positive QFT-G results, TST-positive but QFT-G-negative discordance, and abnormal CXRs consistent with TB. Positive predictive values of TST and QFT-G for an abnormal CXR were 25.9% and 25.6%, respectively. Conclusion. The estimated prevalence of MTBI among US-bound visa applicants in Vietnam based on TST was twice that based on QFT-G, and 14 times higher than a TST-based estimate of MTBI prevalence reported for the general US population in 2000. QFT-G was not better than TST at predicting abnormal CXRs consistent with TB.

No abstract