Specificiteit van de Mantoux-reactie op het nieuwe tuberculine RT23 ten opzichte van de reactie op het oude PPD-RIVM; vergelijkend onderzoek onder ziekenhuispersoneel

In the Netherlands, an increase in prevalence of tuberculin positivity has been noted since the replacement of the Dutch PPD-RIVM preparation by RT23. This investigation was carried out to assess the specificity of RT23 compared with PPD-RIVM.

Design

Comparative.

Method

In 90 hospital workers simultaneous tuberculin tests were performed in both forearms with RT23 (Statens Serum Institut, Copenhagen, Denmark; lot number 13751; 2 tuberculin units) and PPD-RIVM (Rijksinstituut voor Volksgezondheid en Milieu, Bilthoven, the Netherlands; lot number 76B; 1 IU), respectively. Sensitivity to atypical mycobacteria (Mycobacterium scrophulaceum, M. avium and M. kansasii) was assessed where differences were > 3 mm.

Results

In two of 73 non-vaccinated subjects, reactions to RT23 were 11 and 15 mm larger than to PPD-RIVM; both showed sensitivity to M. scrophulaceum and M. avium. Five of nine BCG vaccinated subjects showed differences of five to eight mm; in four of these, the reaction to RT23 was larger. Repeat testing in one showed no cross-reactions. The specificity of RT23 compared with PPD-RIVM was 96 (cut-off at 10 mm diameter).

Conclusions

In a low tuberculosis risk population, tuberculin testing with RT23 yields more positive results than PPD-RIVM. This is probably due to stronger cross-reactivity with atypical mycobacteria of RT23. Decisions on isoniazide prophylaxis should take into account an increased false-positivity rate with RT23.