Childhood tuberculosis and its early diagnosis

A blood RNA signature for tuberculosis disease risk: a prospective cohort study

BACKGROUND

Identification of blood biomarkers that prospectively predict progression of Mycobacterium tuberculosis infection to tuberculosis disease might lead to interventions that combat the tuberculosis epidemic. We aimed to assess whether global gene expression measured in whole blood of healthy people allowed identification of prospective signatures of risk of active tuberculosis disease.

METHODS

In this prospective cohort study, we followed up healthy, South African adolescents aged 12-18 years from the adolescent cohort study (ACS) who were infected with M tuberculosis for 2 years. We collected blood samples from study participants every 6 months and monitored the adolescents for progression to tuberculosis disease. A prospective signature of risk was derived from whole blood RNA sequencing data by comparing participants who developed active tuberculosis disease (progressors) with those who remained healthy (matched controls). After adaptation to multiplex quantitative real-time PCR (qRT-PCR), the signature was used to predict tuberculosis disease in untouched adolescent samples and in samples from independent cohorts of South African and Gambian adult progressors and controls. Participants of the independent cohorts were household contacts of adults with active pulmonary tuberculosis disease.

FINDINGS

Between July 6, 2005, and April 23, 2007, we enrolled 6363 participants from the ACS study and 4466 from independent South African and Gambian cohorts. 46 progressors and 107 matched controls were identified in the ACS cohort. A 16 gene signature of risk was identified. The signature predicted tuberculosis progression with a sensitivity of 66·1% (95% CI 63·2-68·9) and a specificity of 80·6% (79·2-82·0) in the 12 months preceding tuberculosis diagnosis. The risk signature was validated in an untouched group of adolescents (p=0·018 for RNA sequencing and p=0·0095 for qRT-PCR) and in the independent South African and Gambian cohorts (p values <0·0001 by qRT-PCR) with a sensitivity of 53·7% (42·6-64·3) and a specificity of 82·8% (76·7-86) in the 12 months preceding tuberculosis.

INTERPRETATION

The whole blood tuberculosis risk signature prospectively identified people at risk of developing active tuberculosis, opening the possibility for targeted intervention to prevent the disease.

FUNDING

Bill & Melinda Gates Foundation, the National Institutes of Health, Aeras, the European Union, and the South African Medical Research Council.

A Novel Sample Processing Method for Rapid Detection of Tuberculosis in the Stool of Pediatric Patients Using the Xpert MTB/RIF Assay

BACKGROUND

Tuberculosis (TB) is difficult to diagnose in children using molecular tests, because children have difficulty providing respiratory samples. Stool could replace sputum for diagnostic TB testing if adequate sample processing techniques were available.

METHODS

We developed a rapid method to process large volumes of stool for downstream testing by the Xpert MTB/RIF (Xpert) TB-detection assay. The method was tested and optimized on stool samples spiked with known numbers of M. tuberculosis colony forming units (CFU), and stools from M. tuberculosis-infected cynomolgus macaques (Macaca fascicularis). Performance was scored on number of positive Xpert tests, the cycle thresholds (Cts) of the Xpert sample-processing control (SPC), and the Cts of the M. tuberculosis-specific rpoB probes. The method was then validated on 20 confirmed TB cases and 20 controls in Durban, South Africa.

RESULTS

The assay's analytical limit of detection was 1,000 CFU/g of stool. As much as one gram of spiked stool could be tested without showing increased PCR inhibition. In analytical spiking experiments using human stool, 1g samples provided the best sensitivity compared to smaller amounts of sample. However, in Macaques with TB, 0.6g stool samples performed better than either 0.2g or 1.2g samples. Testing the stool of pediatric TB suspects and controls suggested an assay sensitivity of 85% (95% CI 0.6-0.9) and 84% (95% CI 0.6-0.96) for 0.6g and 1.2g stool samples, respectively, and a specificity of 100% (95% CI 0.77-1) and 94% (95% CI 0.7-0.99), respectively.

CONCLUSION

This novel approach may permit simple and rapid detection of TB using pediatric stool samples.

Recent advances in the diagnosis and treatment of childhood tuberculosis

Despite over 2.3 million (26% of global burden) cases of tuberculosis (TB) in India the accurate diagnosis of childhood TB remains a major challenge. Children with TB usually have paucibacillary disease and contribute little to disease transmission within the community. Consequently the treatment of children with TB is often not considered a priority by TB control programmes. Adequate and timely assessment of TB infection in childhood could diminish epidemiological burden as underdiagnosed pediatric patients can eventually evolve in to an active state and have the potential to disseminate the etiological agent Mycobacterium tuberculosis, notably increasing this worldwide public health problem. In this review we discuss the most important recent advances in the diagnosis of childhood TB: (1) Symptom-based approaches, (2) novel immune-based approaches, including in vitro interferon-γ IGRA release assays IGRA tests; and (3) bacteriological and molecular methods that are more rapid and/or less expensive than conventional culture techniques for TB diagnosis and/or drug-resistance testing. Recent advances have improved our ability to diagnose latent infection and active TB in children, nevertheless establishing a diagnosis of either latent infection or active disease in HIV-infected children remains a major challenge.

Serum chitotriosidase activity in pulmonary tuberculosis: response to treatment and correlations with clinical parameters

BACKGROUND

Chitotriosidase is an accepted marker of macrophage activation. In this study, we investigated serum chitotriosidase levels in pulmonary tuberculosis (PTB).

METHODS

Forth-two patients with PTB and 30 healthy subjects were enrolled in the study. The radiological extent of PTB, radiological sequela after treatment, and the degree of smear positivity were assessed. Chitotriosidase levels were measured by a fluorometric method.

RESULTS

The serum chitotriosidase levels of the PTB patients were significantly higher than those of the control subjects (39.73±24.97 vs. 9.63±4.55 nmol/mL/h, P<0.001). After completion of the standard 6-month antituberculous treatment, chitotriosidase levels in PTB patients significantly decreased (10.47±4.54 nmol/mL/h, P<0.001). Chitotriosidase levels correlated significantly with the radiological extent of PTB, degree of smear positivity, and post-treatment radiological sequela score (r=0.439, r=0.449, and r=0.337, respectively).

CONCLUSIONS

This study demonstrated that serum chitotriosidase levels increase in PTB; therefore, chitotriosidase can be used as a marker of disease activity, severity, and response to treatment.

Phage-based platforms for the clinical detection of human bacterial pathogens

Bacteriophages (phages) have been utilized for decades as a means for uniquely identifying their target bacteria. Due to their inherent natural specificity, ease of use, and straightforward production, phage possess a number of desirable attributes which makes them particularly suited as bacterial detectors. As a result, extensive research has been conducted into the development of phage, or phage-derived products to expedite the detection of human pathogens. However, very few phage-based diagnostics have transitioned from the research lab into a clinical diagnostic tool. Herein we review the phage-based platforms that are currently used for the detection of Mycobacterium tuberculosis, Yersinia pestis, Bacillus anthracis and Staphylococcus aureus in the clinical field. We briefly describe the disease, the current diagnostic options, and the role phage diagnostics play in identifying the cause of infection, and determining antibiotic susceptibility.

Microscopic observation drug susceptibility assay (MODS) for early diagnosis of tuberculosis in children

MODS is a novel liquid culture based technique that has been shown to be effective and rapid for early diagnosis of tuberculosis (TB). We evaluated the MODS assay for diagnosis of TB in children in Viet Nam. 217 consecutive samples including sputum (n = 132), gastric fluid (n = 50), CSF (n = 32) and pleural fluid (n = 3) collected from 96 children with suspected TB, were tested by smear, MODS and MGIT. When test results were aggregated by patient, the sensitivity and specificity of smear, MGIT and MODS against "clinical diagnosis" (confirmed and probable groups) as the gold standard were 28.2% and 100%, 42.3% and 100%, 39.7% and 94.4%, respectively. The sensitivity of MGIT and MODS was not significantly different in this analysis (P = 0.5), but MGIT was more sensitive than MODS when analysed on the sample level using a marginal model (P = 0.03). The median time to detection of MODS and MGIT were 8 days and 13 days, respectively, and the time to detection was significantly shorter for MODS in samples where both tests were positive (P<0.001). An analysis of time-dependent sensitivity showed that the detection rates were significantly higher for MODS than for MGIT by day 7 or day 14 (P<0.001 and P = 0.04), respectively. MODS is a rapid and sensitive alternative method for the isolation of M.tuberculosis from children.

Recent advances in the diagnosis of childhood tuberculosis

Children account for a major proportion of the global tuberculosis disease burden, especially in endemic areas. However, the accurate diagnosis of childhood tuberculosis remains a major challenge. This review provides an overview of the most important recent advances in the diagnosis of intrathoracic childhood tuberculosis: (1) symptom-based approaches, including symptom-based screening of exposed children and symptom-based diagnosis of active disease; (2) novel immune-based approaches, including T cell assays and novel antigen-based tests; and (3) bacteriological and molecular methods that are more rapid and/or less expensive than conventional culture techniques for tuberculosis diagnosis and/or drug-resistance testing. Recent advances have improved our ability to diagnose latent infection and active tuberculosis in children, but establishing a diagnosis of either latent infection or active disease in HIV-infected children remains a major challenge, particularly in high-burden settings. Although improved access to diagnosis and treatment is essential, ultimately the burden of childhood tuberculosis is determined by the level of epidemic control achieved in a particular community. Several recent initiatives, in particular the United Nations Millennium Developmental Goals, deal with the problem of poverty and disease in a holistic fashion, but global political commitment is required to support these key initiatives.

Changes in sexual behavior and risk of HIV transmission after antiretroviral therapy and prevention interventions in rural Uganda

BACKGROUND

The impact of antiretroviral therapy (ART) on sexual risk behavior and HIV transmission among HIV-infected persons in Africa is unknown.

OBJECTIVE

To assess changes in risky sexual behavior and estimated HIV transmission from HIV-infected adults after 6 months of ART.

DESIGN AND METHODS

A prospective cohort study was performed in rural Uganda. Between May 2003 and December 2004 a total of 926 HIV-infected adults were enrolled and followed in a home-based ART program that included prevention counselling, voluntary counseling and testing (VCT) for cohabitating partners and condom provision. At baseline and follow-up, participants' HIV plasma viral load and partner-specific sexual behaviors were assessed. Risky sex was defined as inconsistent or no condom use with partners of HIV-negative or unknown serostatus in the previous 3 months. The rates of risky sex were compared using a Poisson regression model and transmission risk per partner was estimated, based on established viral load-specific transmission rates.

RESULTS

Six months after initiating ART, risky sexual behavior reduced by 70% [adjusted risk ratio, 0.3; 95% confidence interval (CI), 0.2-0.7; P = 0.0017]. Over 85% of risky sexual acts occurred within married couples. At baseline, median viral load among those reporting risky sex was 122 500 copies/ml, and at follow-up, < 50 copies/ml. Estimated risk of HIV transmission from cohort members declined by 98%, from 45.7 to 0.9 per 1000 person years.

CONCLUSIONS

Providing ART, prevention counseling, and partner VCT was associated with reduced sexual risk behavior and estimated risk of HIV transmission among HIV-infected Ugandan adults during the first 6 months of therapy. Integrated ART and prevention programs may reduce HIV transmission in Africa.