TRANSMISSION AND RISK FACTORS FOR LATENT TUBERCULOSIS INFECTIONS AMONG INDEX CASE-MATCHED HOUSEHOLD CONTACTS.

An understanding of the risk factors associated with acquiring and transmitting Mycobacterium tuberculosis (MTB) is required for controlling tuberculosis (TB). We aimed to determine the risk factors and transmission factors for latent tuberculosis infection (LTBI) in northeastern Thailand. Household contact persons (n = 70) and matched index patients with pulmonary TB (n = 42) who presented to Srinagarind Hospital, Khon Kaen, Thailand were interviewed from September 1, 2012 to March 31, 2014. LTBI was determined by positive results on both a tuberculin skin test and the QuantiFERON-TB Gold In-Tube test. Multivariate analysis of host and environmental risk factors was performed. Among contact persons, being aged 20 years (adjusted OR=14.0; 95% CI: 1.2-159.5), having a family relationship with a TB subject such as being a spouse or parent (adjusted OR=24.9; 95% CI: 2.4-263.9) and exposure to a TB subject for 5 hours/day (adjusted OR=9.2; 95% CI: 1.4-58.1) were risk factors for LTBI. Having a high bacillary load (adjusted OR=2; 95% CI: 1.26-3.17) or a moderate bacillary load (adjusted OR=1.39; 95% CI: 1.04-1.84) among TB subjects correlated with increased transmissibility compared to having a low bacillary load. The type of dwelling and density of household members were not found to be risk factors for LTBI in our study. We conclude being aged 20 years and having a relationship with a TB patient as a spouse or parent were risk factors for acquiring LTBI, and having a higher bacillary load was a risk factor for transmitting TB. Keywords: latent tuberculosis infection, transmission factor, risk factor, Mycobacterium tuberculosis, interferon-gamma release assay, Thailand

Evaluation of the QuantiFERON?-TB Gold In-Tube assay and tuberculin skin test for the diagnosis of Mycobacterium tuberculosis infection in northeastern Thailand.

BACKGROUND: The diagnosis of latent Mycobacterium tuberculosis infection (LTBI) is currently based on the immunological response of T-cells to M. tuberculosis (MTB) antigens. However, the QuantiFERON®-TB Gold In-Tube assay (QFT) has not yet been evaluated in the Thai adult population. OBJECTIVE: To evaluate the diagnostic performance and determine predictors of discordant results between the QFT and tuberculin skin test (TST). METHODS: Active tuberculosis (ATB) patients (n=54), close contacts (CCs) living in the same household as a TB patient (n=100) and healthy controls (HCs) (n=60) were interviewed and underwent the QFT and TST at Srinagarind Hospital in Thailand. Various cut-off values for the QFT (0.25-0.35 IU/mL) and TST (5-15 mm) were applied. RESULTS: The maximum agreement rate between the tests was 71.5% (κ=0.41) with cut-offs of 0.35 IU/mL and 10 mm or 0.25 IU/mL and 10 mm. Based on standard cut-off values (0.35 IU/mL and 10 mm) and using ATB patients and HCs as positive and negative controls, the TST was more sensitive than the QFT (87.0% vs. 66.7%, respectively), whereas the QFT was more specific than the TST (83.3% vs. 70.0%, respectively). Being underweight (OR 3.86, 95%CI 1.3-11.48) or overweight (OR 5.9, 95%CI 1.24-28.16) was significantly associated with TST+/QFT- results. Diabetes (OR 32.56, 95%CI 1.73-613.49) and poor or fair nutrition (OR 7.4, 95%CI 1.23-44.57) were significantly associated with TST-/QFT+ results. CONCLUSION: The TST should be used as a screening test based on its higher sensitivity, whereas the QFT should be used as a confirmatory test because of its higher specificity.

T-CELL RESPONSES ASSESSED USING IGRA AND TST ARE NOT CORRELATED WITH AFB GRADE AND CHEST RADIOGRAPH IN PULMONARY TUBERCULOSIS PATIENTS.

A definitive marker determining the bacillary load of Mycobacterium tuberculosis (MTB), the causative agent of tuberculosis (TB), and hence disease severity, is required for patient monitoring and management. In this study, the association among T-cell responses based on the interferon-gamma release assay (IGRA) and the tuberculin skin test (TST), the sputum acid-fast bacilli (AFB) grade and types of radiological lesions were analyzed in new cases of pulmonary TB patients (n = 54) at Srinagarind Hospital, Khon Kaen, Thailand between September 1, 2012 and March 31, 2014. It was found that infiltrative and cavitary lesions from chest radiographs were associated with high sputum AFB grade (p = 0.048). T-cell responses from both IGRA and TST were not correlated with sputum AFB grade. Neither IGRA nor TST was correlated with the bacillary load as defined by AFB grade and chest radiographs. Patients with cavitary lesions on chest radiographs tended to have high IFN-γ concentrations and large TST indurations. In addition, TB patients with previous BCG vaccination showed significantly higher IFN-γ induction compared to the non-vaccinated group (p = 0.001). This study showed T-cell responses based on both IGRA and TST were not correlated with AFB grade and chest radiograph. In areas of high rates of BCG vaccination, as in Thailand, the BCG may affect IGRA and TST interpretations.