Value of dual testing for identifying tuberculous infection

Area of Science:

• Infectious Diseases
• Mycobacterial Infections
• Public Health

Background:

• Tuberculosis remains a significant global health challenge, particularly in endemic regions like South India.
• Accurate identification of tuberculous infection is crucial for effective disease control and prevention strategies.

Purpose of the Study:

• To evaluate the efficacy of dual testing using Purified Protein Derivative-Standard (PPD-S) and Purified Protein Derivative-B (PPD-B) for identifying individuals with tuberculous infections.
• To assess the role of non-tuberculous mycobacterial infections in modulating tuberculosis incidence.

Main Methods:

• A large-scale, long-term prospective study involving approximately 240,000 individuals in rural South India.
• Initial dual testing with PPD-S and PPD-B, followed by 15-year follow-up using population surveys every 2.5 years.
• Estimation of culture-positive tuberculosis incidence using life-table analysis.

Main Results:

• Dual testing identified a subgroup with significantly higher tuberculosis incidence among those with intermediate PPD-S reactions (8-11 mm).
• Specific criteria for PPD-S and PPD-B induration sizes were associated with increased risk of culture-positive tuberculosis.
• Infection with non-tuberculous mycobacteria provided approximately 30% protection against developing tuberculosis over the 15-year study period.

Conclusions:

• Dual testing with PPD-S and PPD-B is valuable for identifying tuberculous infections in individuals with intermediate PPD-S reactions.
• A significant proportion of positive reactions in this population were attributed to non-tuberculous mycobacteria, highlighting the importance of differential testing.