No one knows, say Lee et al. They report on 27 Korean soldiers who were exposed to 5 barracks-mates with active TB; 26 eventually "converted" by tuberculin skin test/PPD or by interferon-gamma release assay. One-time TST/PPD identified 21, or 78%. IGRA every two weeks eventually diagnosed 26 (96%), but it took 14 weeks for 3 soldiers' IGRA tests to become positive. Eur Resp J 2011;37:1447-1452.