Dual skin tests with Mycobacterium avium sensitin and PPD to detect misdiagnosis of latent tuberculosis infection.
BACKGROUND
A positive tuberculin skin test (TST) may indicate cross-reacting immunity to non-tuberculous mycobacteria (NTM) and not latent tuberculosis infection (LTBI).


OBJECTIVE
To assess misclassification of LTBI, as assessed by skin testing with Mycobacterium avium sensitin (MaS), and to determine how this misclassification affects the analysis of risk factors for LTBI.


METHODS
In a population-based survey, participants underwent skin testing with M. tuberculosis purified protein derivative (PPD) and MaS. A PPD-dominant skin test was a reaction that was ≥ 3 mm larger than the MaS reaction; a MaS-dominant skin test was a reaction that was ≥ 3 mm larger than the PPD reaction.


RESULTS
Of 447 randomly selected persons, 135 (30%) had a positive PPD test. Of these, 21 (16%) were MaS- dominant, and were therefore attributable to NTM and misclassified as LTBI. PPD reactions of 5-14 mm were more likely to be misclassified than those ≥ 15 mm (OR = 5.0, 95%CI 1.9-13.2). Adjusting for misclassification had only a small impact on the analysis of risk factors for LTBI.


CONCLUSIONS
A substantial number of individuals who are diagnosed with LTBI are actually sensitized to NTM. Using dual skin testing would reduce misdiagnosis and prevent unnecessary treatment.
Boston University School of Public Health, Boston, Massachusetts 02118, USA.
E M
EM
Larson
M
M
O'Donnell
S
S
Chamblee
C R
CR
Horsburgh
B J
BJ
Marsh
J D
JD
Moreland
L S
LS
Johnson
C Fordham
CF
von Reyn
D000293:Adolescent; D000328:Adult; D000941:Antigens / Q000276:immunology; D016009:Chi-Square Distribution; D002648:Child; D002675:Child, Preschool; D003429:Cross Reactions; D003951:Diagnostic Errors / Q000517:prevention & control*; D005260:Female; D005431:Florida / Q000453:epidemiology; D006801:Humans; D007223:Infant; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D008297:Male; D008875:Middle Aged; D009162:Mycobacterium avium / Q000276:immunology*; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D016017:Odds Ratio; D011237:Predictive Value of Tests; D018570:Risk Assessment; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014373:Tuberculin / Q000276:immunology; D014374:Tuberculin Test; D055815:Young Adult
D000941:Antigens; D014373:Tuberculin; C012031:sensitin