Choosing an appropriate cutting point for conversion in annual tuberculin skin testing

Area of Science:

• Public Health
• Infectious Disease Epidemiology
• Occupational Health

Background:

• Previous two-step tuberculin testing reduced booster phenomenon effects but maintained high conversion rates.
• A 10 mm induration cutoff likely caused false conversions due to prevalent nontuberculous mycobacteria sensitivity.

Purpose of the Study:

• To evaluate the impact of increasing the tuberculin skin test (TST) induration cutoff point on employee conversion rates.
• To identify a more accurate TST cutoff for annual screening in high-prevalence areas.

Main Methods:

• Retrospective analysis of employee tuberculin skin testing data.
• Comparison of conversion rates using 10 mm versus 15 mm induration cutoffs.
• Assessment of age dependency and repeat testing reactions in converter populations.

Main Results:

• Increasing the TST cutoff to 15 mm reduced the conversion rate from 2.6% to 1.2%.
• The 15 mm cutoff identified individuals with persistent large reactions.
• Age dependency in the converter population was eliminated.

Conclusions:

• A 15 mm induration cutoff is a more appropriate standard for annual employee tuberculin skin testing.
• This adjustment improves accuracy in regions with common sensitivity to nontuberculous mycobacteria.
• The revised cutoff enhances the reliability of TST for occupational health surveillance.