Risk Factors for Transmission in Asymptomatic Smear-Positive/Cavitary Tuberculosis

Overview

This national cohort study of 20,455 pulmonary TB patients in South Korea identified that 36.4% were asymptomatic, with 25.5% of these having transmission risk factors such as smear positivity or cavitation. Key risk factors for transmission included male sex, low BMI, current smoking, diabetes, and autoimmune diseases, with higher mortality observed in those with transmission risk.

Background

Pulmonary tuberculosis typically presents with respiratory symptoms prompting diagnosis, but asymptomatic active TB cases remain undetected and contribute to ongoing transmission. Active screening is the only method to identify these silent transmitters, who can represent up to half of TB diagnoses in some studies. South Korea has reduced TB incidence but still faces higher transmission rates partly due to undetected asymptomatic cases. Identifying risk factors for transmission and mortality in asymptomatic TB patients is critical for targeted screening and achieving TB control goals.

Data Highlights

Key Findings

• Among 20,455 pulmonary TB patients, 36.4% were asymptomatic.
• Of asymptomatic patients, 25.5% had transmission risk factors (positive sputum smear or cavitation).
• Male sex increased transmission risk (OR 1.385; P <.001).
• Low BMI was strongly associated with transmission risk (OR 1.687; P <.001).
• Current smoking status elevated transmission risk (OR 1.443; P <.001).
• Comorbid diabetes (OR 1.399; P <.001) and autoimmune disease (OR 2.233; P = .004) were significant risk factors.
• Mortality was higher in patients with transmission risk factors (9.3% vs 7.1%; P = .008).

Clinical Implications

Clinicians should consider targeted screening for asymptomatic pulmonary TB patients who are male, have low BMI, currently smoke, or have diabetes or autoimmune diseases, as these factors increase transmission and mortality risks. Early identification and management of these high-risk asymptomatic individuals could reduce TB spread and improve outcomes. Public health strategies should prioritize these risk groups to enhance TB control efforts.

Conclusion

Asymptomatic pulmonary TB patients with specific risk factors such as male sex, low BMI, smoking, diabetes, and autoimmune diseases have increased transmission and mortality risks. Targeted screening in these populations is essential to control TB transmission and improve patient prognosis.

References

1. Korean TB Cohort Study 2018-2021 -- Identifying Risk Factors for Asymptomatic Smear-Positive/Cavitary Tuberculosis Cases