Interaction between C-Tb and PPD given concomitantly in a splitbody randomised controlled trial

SETTING: Seven tuberculosis (TB) clinics in South Africa. OBJECTIVE : As both purified protein derivative (PPD) and a Mycobacterium tuberculosis-specific skin test (C-Tb) contain region of difference 1 (RD1) antigens, we conducted a study to evaluate whether there was any interaction between the two during concomitant and separate administration in patients with newly diagnosed culture-positive TB. DESIGN: Adult patients with active TB (n = 456, 20% human immunodeficiency virus infected) were randomised to receive only C-Tb, only PPD, or concomitant injection of both C-Tb and PPD using the Mantoux technique. Indurations were read after 48-72 h. QuantiFERON (R)-TB Gold In-Tube (QFT) was performed in tandem. RESULTS : Of the 456 study participants, 154 simultaneously received both C-Tb and PPD, 153 only C-Tb and 149 only PPD. There was no effect of concomitant injection of PPD on the mean C-Tb induration (19 mm, 95% CI 17-22 vs. 18 mm, 95% CI 16-21; P = 0.91). In patients with active TB, C-Tb sensitivity (78%) was similar to PPD (81%) and QFT (84%; excluding 82/429 [19%] indeterminate results). All tests showed reduced sensitivity in participants with CD4 <100 cells/mu l. CONCLUSION: In patients with active TB, there was no interaction between C-Tb and PPD during concomitant injection of both agents. Sensitivities were similar for PPD and C-Tb.