Repeat tuberculin testing in BCG-vaccinated subjects in the United Kingdom- The booster effect varies with the time of reading

The booster effect varies between populations, but has not been studied in the UK. The aim of this study was to investigate the effect of repeat tuber culin tests at 1 wk in BCG-vaccinated healthy subjects (all hospital employ ees) in the UK; we have assessed whether a booster effect is present 48 and 72 h after injection. Twenty-six subjects received two tuberculin tests (b oth 10 units) administered by the Mantoux technique-Tests 1 and 2. At Test 2 there was a significant increase in induration at 48 h (mean, 7.8 mm; p < 0.001), no difference at 72 h (mean, 0.2 mm; p = 0.93), and a reduction at 96 h (mean, -4.2 mm; p = 0.02). There were more positive results (>15 mm i nduration) at Test 2 compared with Test 1 at 48 h (19 vs. 9, respectively; p = 0.002), but similar numbers at 72 h (11 vs. 10, respectively). These re sults show that repeat tuberculin testing in this BCG-vaccinated population caused a booster effect that varied with the time of measurement and was m aximal at 48 h.