Role of digital tomosynthesis in the context of tuberculosis contact investigation: comparisons with digital radiography

Subclinical tuberculosis: a meta-analysis of prevalence and scoping review of definitions, prevalence and clinical characteristics

BACKGROUND

This scoping review aimed to characterise definitions used to describe subclinical tuberculosis (TB), estimate the prevalence in different populations and describe the clinical characteristics and treatment outcomes in the scientific literature.

METHODS

A systematic literature search was conducted using PubMed. We included studies published in English between January 1990 and August 2022 that defined "subclinical" or "asymptomatic" pulmonary TB disease, regardless of age, HIV status and comorbidities. We estimated the weighted pooled proportions of subclinical TB using a random-effects model by World Health Organization reported TB incidence, populations and settings. We also pooled the proportion of subclinical TB according to definitions described in published prevalence surveys.

RESULTS

We identified 29 prevalence surveys and 71 other studies. Prevalence survey data (2002-2022) using "absence of cough of any duration" criteria reported higher subclinical TB prevalence than those using the stricter "completely asymptomatic" threshold. Prevalence estimates overlap in studies using other symptoms and cough duration. Subclinical TB in studies was commonly defined as asymptomatic TB disease. Higher prevalence was reported in high TB burden areas, community settings and immunocompetent populations. People with subclinical TB showed less extensive radiographic abnormalities, higher treatment success rates and lower mortality, although studies were few.

CONCLUSION

A substantial proportion of TB is subclinical. However, prevalence estimates were highly heterogeneous between settings. Most published studies incompletely characterised the phenotype of people with subclinical TB. Standardised definitions and diagnostic criteria are needed to characterise this phenotype. Further research is required to enhance case finding, screening, diagnostics and treatment options for subclinical TB.

CT and 18F-FDG PET abnormalities in contacts with recent tuberculosis infections but negative chest X-ray

Close contacts of individuals with pulmonary tuberculosis are at risk for tuberculosis infection and the development of active tuberculosis. In current contact investigations, immunologic tests (the tuberculin skin test and interferon-gamma release assay) and chest X-ray examinations are used to dichotomize contacts with Mycobacterium tuberculosis infections into those with active (X-ray abnormalities) versus latent tuberculosis (normal radiographs). This article is a critical review of computed tomographic (CT) and 18-fluorodeoxyglucose positron emission tomographic (PET) findings of incipient tuberculosis without X-ray abnormalities based on a systematic literature review of twenty-five publications. The CT and 18-fluorodeoxyglucose PET studies revealed minimal pauci-nodular infiltrations in the lung parenchyma and mediastinal lymph nodes abnormalities with metabolic uptake in approximately one-third of asymptomatic close contacts with negative chest radiographic and bacteriological/molecular results for active tuberculosis. Tuberculosis with minimal changes challenge the validity of simply dichotomizing cases of recent M. tuberculosis infections in contacts depending on the presence of X-ray abnormalities as the recent infections may spontaneously regress, remain stagnant, or progress to active tuberculosis in human and nonhuman primate studies. Whether contacts with tuberculosis with minimal changes are interpreted as having active tuberculosis or latent tuberculosis has clinical implications in terms of specific benefits and harms under the current contact management. Advanced imaging tools may help further stratify contacts intensely exposed to M. tuberculosis on a continuous spectrum from latent tuberculosis to incipient, subclinical and active tuberculosis. Identifying incipient tuberculosis would provide an opportunity for earlier and tailored treatment before active tuberculosis is established.