New Delhi, Oct 28 (NationPress) A study published in The Lancet Global Health reveals that standard chest X-rays, which rely on symptoms, are insufficient for identifying asymptomatic tuberculosis (TB) infections among household contacts. Conducted by researchers from the University of Cape Town, South Africa, the study involved systematic screening with universal sputum microbiological testing of 979 household contacts of individuals diagnosed with pulmonary tuberculosis across three communities in South Africa.

The researchers evaluated the effectiveness of tuberculosis symptom screening (regardless of duration) and chest radiograph assessments (noting any abnormalities indicative of active TB) against a microbiological reference standard.

The findings showed that 5.2% of household contacts were confirmed to have pulmonary tuberculosis, with 82.4% of these individuals presenting no symptoms. Alarmingly, chest radiographs failed to identify 40% of the TB cases.

“Over 80% of the confirmed TB cases among household contacts were asymptomatic; chest radiograph screenings missed more than 40% of these,” stated Dr. Simon C Mendelsohn, the corresponding author from the South African Tuberculosis Vaccine Initiative. He emphasized that “community prevalence surveys based on symptom and chest radiograph screenings could significantly underestimate the prevalence of asymptomatic tuberculosis in endemic areas.”

According to the World Health Organization (WHO), around 2.7 million people (25% of the estimated 10.8 million TB cases worldwide) were undiagnosed or untreated in 2023.

Identifying and treating these so-called missing millions is critical, but the challenge lies in the fact that a majority remain asymptomatic.

“More than half of all TB identified in community prevalence surveys is categorized as asymptomatic, affecting individuals who do not exhibit or recognize typical TB symptoms, such as cough, fever, night sweats, and weight loss,” the authors noted.

In this study, asymptomatic tuberculosis in household contacts exhibited low bacterial loads and low serum C-reactive protein levels, comparable to healthy individuals. However, these differed from symptomatic tuberculosis in a group of clinic attendees.

The sensitivity of chest radiograph screening for asymptomatic tuberculosis was found to be only 56.1%, while the combined sensitivity for symptom and chest radiograph screening for all tuberculosis was slightly higher at 64.0%.

“Our results indicate that symptom-based and chest radiograph-based methods are inadequate for community TB screening and fall short of the WHO’s target product profile for a TB screening test, which requires a minimum of 90% sensitivity and 70% specificity. National surveys that do not include universal sputum microbiological testing may significantly underestimate the prevalence of asymptomatic tuberculosis in high-burden nations,” Mendelsohn concluded.