Phenotypic variability in childhood TB: Implications for diagnostic endpoints in tuberculosis vaccine trials

Subclinical tuberculosis in children: diagnostic strategies for identification reported in a 6-year national prospective surveillance study

BACKGROUND

Subclinical tuberculosis (TB) is well recognized and defined as a disease state with absent or non-recognized symptoms. The study identifies factors associated with subclinical TB and diagnostic strategies in a low-burden, high-resource country.

METHODS

Data was collected between December 2013 to November 2019 through the Swiss Pediatric Surveillance Unit (SPSU). Children with culture/molecular confirmed TB, or who were treated with ≥3 anti-mycobacterial drugs, were included.

RESULTS

A total of 138 (80%) children with TB disease were included in the final analysis, of which 43 (31%) were subclinical. The median age of children with subclinical compared to symptomatic TB was 3.7(IQR 2.2 to 7) and 9.7(IQR 2.7 to 14.3) years, respectively (p=0.003). The cause of investigation for TB was recorded in 31/43 (72.1%) of children with subclinical TB, and included contact exposure in 25 (80.6%). In children with subclinical TB, diagnosis was made by a combination of the following abnormal/confirming results: culture/molecular + immunodiagnostic + chest radiography in 12 (27.9%), immunodiagnostic + chest radiography in 19 (44.2%), culture/molecular + chest radiography in 2 (4.7%), culture + immunodiagnostic in 1 (2.3%), chest radiography only in 8 (18.6%) and immunodiagnostic only in 1 (2.3%) case.

CONCLUSION

A notable proportion of children with TB had subclinical disease. This highlights the importance of non-symptom-based TB case finding in exposed children and refugees from high-TB-prevalence settings. TB screening in these asymptomatic children should therefore include a combination of immunodiagnostic testing and imaging followed by culture and molecular testing.

Positive Mycobacterium tuberculosis Gastric Lavage Cultures from Asymptomatic Children With Normal Chest Radiography

Mycobacterium tuberculosis culture from gastric lavage from apparently healthy children following tuberculin skin test conversion, despite normal chest radiography (CR), is well known but is a contentious subject. A consensus statement regarding classification of childhood tuberculosis excluded this condition, stating that more data were needed. To assist in this discussion, we reviewed early publications that reported the occurrence of this phenomenon and early anatomical pathology studies that described changes that occur in children following tuberculosis infection. Pathology studies describe frequent cavitation in primary foci in children from whom positive M. tuberculosis cultures might easily arise. These foci were very small in some children who might have normal CR. Positive cultures might also arise from ulcerated mediastinal lymph nodes that are invisible on CR. Young children with recent infection very likely have active primary pulmonary tuberculosis.

Anton Ghon and His Colleagues and Their Studies of the Primary Focus and Complex of Tuberculosis Infection and Their Relevance for the Twenty-First Century

Anton Ghon is well known in the field of childhood tuberculosis, and the tuberculosis primary focus and complex are frequently called the Ghon focus and complex; this is largely the result of the wide publication of the English translation of his monograph "Der primäre Lungenherd bei der Tuberkulose der Kinder." Ghon's studies are frequently quoted, but precise details of his monograph are neglected, his results often misquoted, and his later publications virtually unknown. This review highlights aspects of Ghon's anatomical pathology studies in children and adults not necessarily dying of tuberculosis but with signs of tuberculosis infection. Ghon found a single primary tuberculosis focus in approximately 80% of tuberculosis-infected children situated close to the pleura in two-thirds of cases. Cavitation of the focus was common, and lymphatic spread involved lymph nodes in the abdomen and neck in many children. Studies amongst adults and children frequently found the healed primary tuberculosis focus to be completely calcified without histological signs of tuberculosis activity; however, particularly in the presence of pulmonary tuberculosis, histological signs of tuberculosis activity were often found in the lymph nodes of the angulus venosus, despite apparent healing with extensive calcification. Both earlier studies and more recent investigations, with molecular biological tools, unavailable to Ghon and earlier researchers, have confirmed the presence of viable mycobacteria in apparently normal or healed thoracic nodes and also found molecular biological indications of viable mycobacteria in these nodes. As suggested by Ghon, lympho-haematogenous spread of tuberculosis may be more common than is usually appreciated.

The Role of Clinical Symptoms in the Diagnosis of Intrathoracic Tuberculosis in Young Children

BACKGROUND

Childhood tuberculosis (TB) is usually Mycobacterium tuberculosis (MTB) culture negative. Furthermore, clinical presentation may be altered by active case finding, isoniazid prophylaxis and early treatment. We aimed to establish the value of presenting symptoms for intrathoracic TB case diagnosis among young children.

METHODS

Healthy, HIV-uninfected, South African infants in an efficacy trial of a novel TB vaccine (MVA85A) were followed for 2 years for suspected TB. When suspected, investigation followed a standardized algorithm comprising symptom history, QuantiFERON Gold-in-Tube, chest radiography (CXR), MTB culture and Xpert MTB/RIF from paired gastric lavage and induced sputa. Adjusted odds ratios and 95% confidence intervals describe the associations between symptoms and positive MTB culture or Xpert MTB/RIF, and CXR compatible with intrathoracic TB.

RESULTS

Persistent cough was present in 172/1017 (16.9%) of the children investigated for TB. MTB culture/Xpert MTB/RIF was positive in 38/1017 children (3.7%); and CXR was positive, that is, compatible with intrathoracic TB, in 131/1017 children (12.9%). Children with persistent cough had more than triple the odds of a positive MTB culture/Xpert MTB/RIF (adjusted odds ratios: 3.3, 95% confidence interval: 1.5-7.0) and positive CXR (adjusted odds ratios: 3.5, 95% confidence interval: 2.2-5.5). Persistent cough was the only symptom that differentiated children with severe (56.5%) from nonsevere intrathoracic TB disease (28.2%; P = 0.001).

CONCLUSION

Persistent cough was the cardinal diagnostic symptom associated with microbiologic and radiologic evidence, and disease severity, of intrathoracic TB. Symptom-based definitions of TB disease for diagnostic, preventive and therapeutic studies should prioritize persistent cough above other symptoms compatible with childhood TB.

Chest Radiographs for Pediatric TB Diagnosis: Interrater Agreement and Utility

The chest radiograph (CXR) is considered a key diagnostic tool for pediatric tuberculosis (TB) in clinical management and endpoint determination in TB vaccine trials. We set out to compare interrater agreement for TB diagnosis in western Kenya. A pediatric pulmonologist and radiologist (experts), a medical officer (M.O), and four clinical officers (C.Os) with basic training in pediatric CXR reading blindly assessed CXRs of infants who were TB suspects in a cohort study. C.Os had access to clinical findings for patient management. Weighted kappa scores summarized interrater agreement on lymphadenopathy and abnormalities consistent with TB. Sensitivity and specificity of raters were determined using microbiologically confirmed TB as the gold standard (n = 8). A total of 691 radiographs were reviewed. Agreement on abnormalities consistent with TB was poor; k = 0.14 (95% CI: 0.10–0.18) and on lymphadenopathy moderate k = 0.26 (95% CI: 0.18–0.36). M.O [75% (95% CI: 34.9%–96.8%)] and C.Os [63% (95% CI: 24.5%–91.5%)] had high sensitivity for culture confirmed TB. TB vaccine trials utilizing expert agreement on CXR as a nonmicrobiologically confirmed endpoint will have reduced specificity and will underestimate vaccine efficacy. C.Os detected many of the bacteriologically confirmed cases; however, this must be interpreted cautiously as they were unblinded to clinical features.

To x-ray or not to x-ray? Screening asymptomatic children for pulmonary TB: a retrospective audit

OBJECTIVE

Recent studies found that a chest x-ray (CXR) has limited value in the assessment of asymptomatic adults with tuberculosis (TB) infection. We aimed to determine in asymptomatic children with a positive tuberculin skin test and/or interferon-γ release assay (TST/IGRA) whether a CXR identifies findings suggestive of pulmonary TB.

DESIGN, SETTING AND PATIENTS

All children with TB infection (defined as TST ≥10 mm and/or positive IGRA) presenting to The Royal Children's Hospital Melbourne during a 54-month period were included. All CXRs were reviewed by a senior radiologist blinded to the clinical details. The medical records of those with radiological abnormalities suggestive of TB were examined to identify those who were asymptomatic when the CXR was done. Demographical data were also collected.

RESULTS

CXRs were available for 268 of 330 TB-infected children, of whom 60 had CXR findings suggestive of TB. Of the 57 for whom clinical details were available, 26 were asymptomatic. Of these asymptomatic children with radiological abnormalities suggestive of TB, 6 had CXR findings suggestive of active TB, 14 had CXR findings suggestive of prior TB and 6 had isolated non-calcified hilar lymphadenopathy. The six with findings suggestive of active TB represented 2.6% (95% CI 0.9 to 5.5%) of asymptomatic TST/IGRA-positive children with evaluable CXRs. One child with isolated hilar lymphadenopathy had microbiologically-confirmed TB.

CONCLUSIONS

In contrast to the results from studies in adults, a CXR identified a small but noteworthy number of children with findings suggestive of pulmonary TB in the absence of clinical symptoms.

Lessons learnt from the first efficacy trial of a new infant tuberculosis vaccine since BCG

BACKGROUND

New tuberculosis (TB) vaccines are being developed to combat the global epidemic. A phase IIb trial of a candidate vaccine, MVA85A, was conducted in a high burden setting in South Africa to evaluate proof-of-concept efficacy for prevention of TB in infants.

OBJECTIVE

To describe the study design and implementation lessons from an infant TB vaccine efficacy trial.

METHODS

This was a randomised, controlled, double-blind clinical trial comparing the safety and efficacy of MVA85A to Candin control administered to 4-6-month-old, BCG-vaccinated, HIV-negative infants at a rural site in South Africa. Infants were followed up for 15-39 months for incident TB disease based on pre-specified endpoints.

RESULTS

2797 infants were enrolled over 22 months. Factors adversely affecting recruitment and the solutions that were implemented are discussed. Slow case accrual led to six months extension of trial follow up.

CONCLUSION

The clinical, regulatory and research environment for modern efficacy trials of new TB vaccines are substantially different to that when BCG vaccine was first evaluated in infants. Future infant TB vaccine trials will need to allocate sufficient resources and optimise operational efficiency. A stringent TB case definition is necessary to maximize specificity, and TB case accrual must be monitored closely.

Clinical trials of TB vaccines: harmonization and cooperation

A new efficacious tuberculosis (TB) vaccine has the potential to dramatically assist control efforts for the global TB epidemic. Good progress has been made with the clinical development of new TB vaccine candidates with twelve being actively tested in clinical trials. However, there are many challenges that need to be addressed before a new vaccine is licensed for public use. The diversity of risk in populations needs to be factored into clinical development plans, specific but feasible clinical endpoints need to be agreed upon, and TB vaccines need to be effective in both uninfected and infected populations. An achievable efficacy target needs to be set while standardisation of trial outcomes and critical choices based on the vaccine development pipeline need to be made. Alternative routes of vaccine administration should be thoroughly explored, sufficient adequately prepared trial sites for performing TB vaccine assessments are required and creative use of study designs should be used to expedite progress towards licensure while at the same time containing costs. Lastly, there needs to be sufficient funding to support TB vaccine development. These challenges can be met through commitment by all role-players within the TB vaccine arena and with support from external stakeholders.

Consensus statement on diagnostic end points for infant tuberculosis vaccine trials

BACKGROUND

 Definition of clinical trial end points for childhood tuberculosis is hindered by lack of a standard case definition. We aimed to identify areas of consensus or debate on potential end points for tuberculosis vaccine trials among human immunodeficiency virus-uninfected children.

METHODS

 Thirty-eight opinion leaders participated in a Consensus Workshop at the Second Global Forum on TB Vaccines (Estonia, 2010). Outcomes were categorized as unanimity, modified consensus, or lack of consensus. Individual reservations were noted.

RESULTS

 Modified consensus was achieved on 3 issues: (1) unsuitability of historical BCG trial end points as sole primary end points for modern infant trials; (2) symptomatic, complicated intrathoracic tuberculosis as an uncommon but clinically relevant disease phenotype; (3) primary complex tuberculosis in younger children as a common, high-risk phenotype, with a high rate of spontaneous resolution. Participants agreed that radiologic diagnosis of intrathoracic tuberculosis would be based primarily on hilar lymphadenopathy. Lack of consensus was noted for (1) significance of isolated culture of Mycobacterium tuberculosis and (2) the need for evidence of prior tuberculosis exposure to support a diagnosis of tuberculosis disease. Reservations were expressed regarding use of interferon-γ release assays and the clinical relevance, and potential for misclassification, of primary complex tuberculosis.

CONCLUSIONS

 The Workshop did not achieve consensus on a single primary end-point definition. Tuberculosis disease phenotypes with optimal diagnostic certainty will be uncommon in the study population. Criteria for composite or multiple end points were identified, and we propose a hierarchy of end-point criteria, based on rate of occurrence, clinical relevance, and diagnostic certainty.