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PPD RT23 for tuberculin surveys in India.

SETTING
Tuberculosis sanatoria and villages in Bangalore district.


OBJECTIVES
To study the appropriateness of continuing to use 1TU dilutions prepared by the BCG Laboratory, Guindy, in Chennai, India, from a freeze-dried form of PPD RT23 with Tween 80 received from Statens Serum Institut (SSI), Copenhagen, for tuberculin surveys in India.


DESIGN
The responses to dual tuberculin tests were compared among: 1) 63 smear-positive cases using 2TU PPD prepared by the Guindy laboratory (Dilution-G), and 2TU PPD prepared by the SSI (Dilution-S); 2) 124 smear-positive cases using 1TU and 2TU Dilution-G; and 3) 1,338 apparently healthy children using 1TU and 2TU Dilution-G. Test sites were allocated randomly using the double-blind technique. Tuberculin responses obtained during studies conducted in India and in other countries were compared.


RESULTS
The differences in sensitivity of tuberculin testing using the different preparations were found to be small and statistically non-significant. Among children, a higher proportion of reaction sizes in 10-14 mm and 15 + mm categories was observed to 2TU compared to 1TU of Dilution-G. This could reflect lower specificity of 2TU in the study area where non-specific sensitivity is highly prevalent. Studies in India and other countries do not suggest any loss in potency of 1TU PPD RT23 with Tween 80.


CONCLUSION
1TU dilutions of PPD RT23 with Tween 80 provided by the BCG Laboratory, Guindy, may continue to be used for tuberculin surveys in India.