Subclinical disease among people with culture-confirmed pulmonary TB in Singapore

Who

• Population: Singapore citizens and permanent residents with sputum culture–confirmed pulmonary tuberculosis (TB)

• Sample size: 18,693 pulmonary TB cases

• Key characteristics: Subclinical TB patients were older (median age 62–63 years) and predominantly male (~75%). High-risk groups included individuals aged ≥70 years and those with immunocompromising conditions (renal failure, steroid therapy, malignancy, HIV).

• Exclusions: Patients with extrapulmonary TB

What

• Focus: Description of the subclinical TB disease spectrum, identification of risk factors, and evaluation of diagnostic methods to improve TB control.

• Findings:

  • Subclinical TB was common: 41.6% met definition 1 (culture-positive with no cough or cough <2 weeks) and 31.6% met definition 2 (culture-positive with no cough).

  • Most subclinical cases had abnormal chest X-rays (~96%), and a substantial proportion had high sputum smear positivity, indicating potential infectiousness despite minimal symptoms.

  • Subclinical TB was independently associated with older age, male sex, immunocompromising conditions, known TB contact, and positive sputum TB PCR.

  • Diagnostic performance of models was moderate (AUC 0.69–0.72).

• Implications: Symptom-based screening alone is insensitive; relying solely on culture confirmation may delay diagnosis and increase transmission.

When

• Study period: January 1, 2004 to December 31, 2023

Where

• Setting: Singapore, using data from the Singapore National TB Registry

Why

• To address gaps in TB control by characterizing subclinical TB, which may be missed by symptom-based screening, particularly in moderate-incidence settings, and to inform more effective screening strategies.

How

• Design: Retrospective registry-based analysis

• Data sources: Mandatory TB notification data, including demographics, clinical presentation, laboratory results, and treatment outcomes

• Definitions: Two operational definitions of subclinical TB based on cough duration/absence

• Analysis: Logistic regression with stepwise forward selection; odds ratios and adjusted odds ratios with 95% confidence intervals; ROC curve analysis to assess model fit

Source: Chew, Y.R., Tay, J.Y., Kyaw, W.M., Chia, P.Y. and Ng, D.H.L., 2025. Subclinical disease among people with culture-confirmed pulmonary tuberculosis in Singapore-a retrospective study. International Journal of Infectious Diseases, 153, p.107768.