Chest X-rays inadequate to detect asymptomatic TB among household contacts: The Lancet

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Commonly used chest X-rays, based on symptoms, are inadequate to detect asymptomatic tuberculosis (TB) infection among household contacts, according to a study published in the journal The Lancet Global Health.

Researchers from the University of Cape Town, South Africa, conducted systematic screening with universal sputum microbiological testing of 979 household contacts of people with pulmonary tuberculosis in three South African communities.

They compared tuberculosis symptom (any duration) and chest radiograph (any abnormality indicative of active tuberculosis) screening approaches against a microbiological reference standard.

The team confirmed pulmonary tuberculosis in 5·2 per cent of household contacts, and 82·4 per cent of these reported no symptoms. Alarmingly, the chest radiographs were not able to detect 40 per cent of the cases.

"More than 80 per cent of confirmed people with tuberculosis among household contacts were asymptomatic; chest radiograph screening missed more than 40 per cent of these," said corresponding author Dr Simon C Mendelsohn, South African Tuberculosis Vaccine Initiative, at the varsity.

"Community prevalence surveys reliant on symptom-based and chest radiograph-based approaches might substantially underestimate the prevalence of asymptomatic tuberculosis in endemic countries," he added.

According to the World Health Organization (WHO), approximately 2·7 million (25 per cent) of the estimated 10·8 million people with tuberculosis worldwide went undiagnosed or untreated in 2023.

While finding and treating these so-called missing millions is crucial, the challenge is that a majority of these remain asymptomatic.

"More than half of all tuberculosis found in community prevalence surveys has been classified as asymptomatic, occurring in people who do not have, recognise, or report typical tuberculosis symptoms such as cough, fever, night sweats, and loss of weight," the team said in the paper.

In the study, asymptomatic tuberculosis in household contacts had low bacterial load, and were also associated with low serum C-reactive protein concentrations that were indistinguishable from those of healthy controls. However, these were distinct from symptomatic tuberculosis in a comparator group of clinic attendees.

Sensitivity of chest radiograph screening for asymptomatic tuberculosis was only 56·1 per cent; sensitivity of combined symptom and chest radiograph screening for all tuberculosis was marginally higher at 64·0 per cent.

"Our findings from household contacts suggest that symptom-based and chest radiograph-based approaches are inadequate for community tuberculosis screening and do not meet the WHO target product profile for a tuberculosis screening test (minimum 90 per cent sensitivity, 70 per cent specificity). National tuberculosis prevalence surveys that omit universal sputum microbiological testing might substantially underestimate the prevalence of asymptomatic tuberculosis in high-burden countries," Mendelsohn said.

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