From Latent Tuberculosis Infection to Tuberculosis. News in Diagnostics (QuantiFERON-Plus)

QuantiFERON-TB Gold Plus Test in Diagnostics of Latent Tuberculosis Infection in Children Aged 1-14 in a Country with a Low Tuberculosis Incidence

The aim of the study was to evaluate the QuantiFERON-TB Gold Plus (QFT-Plus) test usability in the identification of latent tuberculosis infection (LTBI) in children and the determination of features associated with tuberculin skin test (TST) and QFT-Plus-positive results concerning LTBI. Two-hundred thirteen children aged 1–14 were screened for LTBI due to household contact with TB, suspected TB, or were qualified for biological therapy. The objective of this study was to evaluate the QFT-Plus affectivity as a diagnostic test in the absence of a gold standard (GS) test for the diagnosis of LTBI. The children were diagnosed with QFT-Plus, TST, and culture of TB. The QFT-Plus results were analyzed depending on the children’s age, TST size, and type. In children aged 1–4, the positive predictive value of QFT-Plus was 1, the negative predictive value was 0.94, QFT-Plus sensitivity was 75%, and specificity was 100%. It was observed that in children aged 5–14 years, the level of agreement decreased to the substantial, i.e., 87.2%. Moreover, the negative predictive value was 0.83. QFT-Plus sensitivity was 64%, and specificity was 100%. Statistical analysis of QFT-Plus and TST results showed substantial and almost perfect agreements. Our study suggests that QFT-Plus is helpful in a pediatric practice showing good sensitivity and specificity for LTBI. The BCG vaccine, infections, and concomitant morbidities do not affect QFT-Plus results.

Detecting tuberculosis in pregnant and postpartum women in Eswatini

Background

Tuberculosis diagnosis in pregnancy is complex because tuberculosis symptoms are often masked by physiological symptoms of pregnancy. Untreated tuberculosis in pregnant and postpartum women may lead to maternal morbidity and low birth weight. Tuberculosis in HIV-positive pregnant women increases the risk of maternal and infant mortality.

Objective

This study aimed to determine tuberculosis prevalence stratified by HIV status and identify screening algorithms that maximise detection of active tuberculosis among pregnant and postpartum women in Eswatini.

Methods

Women were enrolled at antenatal and postnatal clinics in Eswatini for tuberculosis screening and diagnostic investigations from 01 April to 30 November 2015 in a cross-sectional study. Sputum samples were collected from all participants for tuberculosis diagnostic tests (smear microscopy, GeneXpert, MGIT culture). Blood and urine samples were collected from HIV-positive women for cluster-of-differentiation-4 cell count, interferon gamma release assay and tuberculosis lateral flow urine lipoarabinomannan tests.

Results

We enrolled 990 women; 52% were pregnant and 47% were HIV-positive. The prevalence of tuberculosis among HIV-positive pregnant women was 5% (95% confidence interval [CI]: 2-7) and among postpartum women it was 1% (95%CI: -1-3). Tuberculosis prevalence was 2% (95%CI: 0-3) in HIV-negative pregnant women and 1% (95%CI: -1-2) in HIV-negative postpartum women. The national tuberculosis symptom screening tool failed to identify women who tested tuberculosis-culture positive.

Conclusion

Routine tuberculosis symptom screening alone is insufficient to rule out tuberculosis in pregnant and postpartum women. Only sputum culture maximised the detection of tuberculosis, indicating a need to balance access and cost in developing countries.

Interferon Gamma Release Assays in Patients with Respiratory Isolates of Non-Tuberculous Mycobacteria - a Preliminary Study

Interferon gamma releasing assays (IGRAs) are extensively used in the diagnosis of latent tuberculosis infections. Comparing to tuberculin skin test (TST) they lack false positive results in the populations vaccinated with BCG, and in most non-tuberculous mycobacteria (NTM) infections. Nevertheless, Mycobacterium kansasii, Mycobacterium marinum, and Mycobacterium szulgai may induce positive IGRAs due to RD1 homology with Mycobacterium tuberculosis. The aim of the study was to investigate the possible influence of NTM respiratory isolates on the results of IGRAs. 39 patients (23 females and 16 males) of median age 61 years, with negative medical history concerning tuberculosis, entered the study. Identification of NTM was performed using the niacin test and molecular method GenoType CM test (Hain Lifescience). QFT-Plus was performed in 17 patients, T-SPOT-Tb - in 23 patients. Chest X-rays and a high-resolution computed tomography of the chest have been reviewed by the experienced radiologist blinded to the results of IGRAs, in search of past tuberculosis signs. Positive IGRAs results were obtained in three out of 39 patients (8%): 22% of patients with M. kansasii isolates and 18% of patients with radiological signs on HRCT that might be suggestive of past tuberculosis. Positive IGRAs correlated with radiological signs suggestive of past tuberculosis (r = 0.32, p = 0.04), and on the borderline with isolation of M. kansasii (r = 0.29, p = 0.06). These findings may suggest that a positive IGRAs result, in our material, could depend mostly on asymptomatic past Tb infection. The cross-reactivity of M. kansasii isolates with IGRAs was less probable; nevertheless, it requires further investigations.

Interferon gamma releasing assays (IGRAs) are extensively used in the diagnosis of latent tuberculosis infections. Comparing to tuberculin skin test (TST) they lack false positive results in the populations vaccinated with BCG, and in most non-tuberculous mycobacteria (NTM) infections. Nevertheless, Mycobacterium kansasii, Mycobacterium marinum, and Mycobacterium szulgai may induce positive IGRAs due to RD1 homology with Mycobacterium tuberculosis. The aim of the study was to investigate the possible influence of NTM respiratory isolates on the results of IGRAs. 39 patients (23 females and 16 males) of median age 61 years, with negative medical history concerning tuberculosis, entered the study. Identification of NTM was performed using the niacin test and molecular method GenoType CM test (Hain Lifescience). QFT-Plus was performed in 17 patients, T-SPOT-Tb – in 23 patients. Chest X-rays and a high-resolution computed tomography of the chest have been reviewed by the experienced radiologist blinded to the results of IGRAs, in search of past tuberculosis signs. Positive IGRAs results were obtained in three out of 39 patients (8%): 22% of patients with M. kansasii isolates and 18% of patients with radiological signs on HRCT that might be suggestive of past tuberculosis. Positive IGRAs correlated with radiological signs suggestive of past tuberculosis (r = 0.32, p = 0.04), and on the borderline with isolation of M. kansasii (r = 0.29, p = 0.06). These findings may suggest that a positive IGRAs result, in our material, could depend mostly on asymptomatic past Tb infection. The cross-reactivity of M. kansasii isolates with IGRAs was less probable; nevertheless, it requires further investigations.

Characterization of Two New Multidrug-Resistant Strains of Mycobacterium smegmatis: Tools for Routine In Vitro Screening of Novel Anti-Mycobacterial Agents

Mycobacterium tuberculosis is a pathogen of global public health concern. This threat is exacerbated by the emergence of multidrug-resistant and extremely-drug-resistant strains of the pathogen. We have obtained two distinct clones of multidrug-resistant Mycobacterium smegmatis after gradual exposure of Mycobacterium smegmatis mc² 155 to increasing concentrations of erythromycin. The resulting resistant strains of Mycobacterium smegmatis exhibited robust viability in the presence of high concentrations of erythromycin and were found to be resistant to a wide range of other antimicrobials. They also displayed a unique growth phenotype in comparison to the parental drug-susceptible Mycobacterium smegmatis mc² 155, and a distinct colony morphology in the presence of cholesterol. We propose that these two multidrug-resistant clones of Mycobacterium smegmatis could be used as model organisms at the inceptive phase of routine in vitro screening of novel antimicrobial agents targeted against multidrug-resistant Mycobacterial tuberculosis.