Diagnosis of latent tuberculosis by ELISPOT assay and tuberculin skin test.

OBJECTIVE

To determine the prevalence of latent tuberculosis infection (LTBI) in college students.

PATIENTS AND

METHODS

Four hundred and twenty newly admitted college students were enrolled. The Enzyme-Linked ImmunoSpot assay (ELISPOT) was used. Overall, 171 students with ELISPOT assay+/TST+ were monitored for three years to detect active TB disease.

RESULTS

The overall positive rate of ELISPOT assay was 40.7% among TST+ students. The ELISPOT positive rates were 36.9%, 45.4%, and 64.3% in groups of TST induration of 10-14mm, 15-20mm, and ≥20mm, respectively, with a significant difference (χ(2)=10.136, P<0.01) but no significant difference between BCG scar and no scar (41.2% vs. 38.8%; P>0.05). None of the 171 untreated students contracted active TB within the three-year monitoring period.

CONCLUSION

The LTBI rate might be overestimated by TST compared with interferon-γ release assays. On the basis of a close monitoring, few students developed active TB despite a positive result to the TST and ELISPOT assay.