PPD RT23 for tuberculin surveys in India.

Area of Science:

• Mycobacteriology
• Immunology
• Public Health

Background:

• Tuberculosis (TB) surveys in India rely on tuberculin testing.
• The BCG Laboratory in Guindy, India, prepares purified protein derivative (PPD) RT23 with Tween 80 for these surveys.
• The potency of these PPD dilutions is crucial for accurate survey results.

Purpose of the Study:

• To evaluate the appropriateness of using 1TU dilutions of PPD RT23 with Tween 80 prepared by the BCG Laboratory, Guindy, for tuberculin surveys in India.
• To compare the efficacy of PPD dilutions prepared locally versus those from Statens Serum Institut (SSI).

Main Methods:

• Dual tuberculin tests were conducted in Bangalore district, India.
• Responses were compared between PPD dilutions from Guindy (Dilution-G) and SSI (Dilution-S) in smear-positive TB cases.
• 1TU and 2TU Dilution-G were tested in smear-positive cases and healthy children.
• Randomized, double-blind allocation of test sites was employed.

Main Results:

• Differences in tuberculin test sensitivity between PPD preparations were small and not statistically significant.
• No loss of potency was detected in 1TU PPD RT23 with Tween 80 from the Guindy laboratory.
• Higher reaction sizes were observed with 2TU compared to 1TU in children, potentially indicating lower specificity in areas with high non-specific sensitivity.

Conclusions:

• The 1TU dilutions of PPD RT23 with Tween 80 prepared by the BCG Laboratory, Guindy, are suitable for continued use in Indian tuberculin surveys.
• The findings support the reliability of locally prepared tuberculin antigens for national TB surveillance programs.