Using ELISPOT to expose false positive skin test conversion in tuberculosis contacts

Abstract number: 1733_1121

Hill P., Jeffries D., Brookes R., Fox A., Jackson-Sillah D., Lugos M., Donkor S., de Jong B., Corrah T., Adegbola R., McAdam K.

Objectives: Repeat tuberculin skin tests may be false positive due to boosting of waned immunity to past mycobacterial exposure. We evaluated whether an the booster ELISPOT test could be used to distinguish new Mycobacterium tuberculosis infection from phenomenon.

Methods: We conducted tuberculin and ELISPOT tests in 1,665 TB contacts: 799 were tuberculin test negative and were offered a repeat test after 3 months. Those test positive with ≥6 mm increased induration had an ELISPOT, chest X-ray and sputum analysis if appropriate. We compared converters with non-converters and assessed the probability of each of 4 combinations of ELISPOT results.

Results: 704 (72%) contacts had a repeat tuberculin test; 176 (25%) had test conversion, which increased with exposure to a case (p = 0.002), increasing age (p = 0.0006) and BCG scar (p = 0.06). 114 tuberculin test converters had ELISPOT results: 16 (14%) were recruitment positive/follow up positive, 9 (8%) positive/negative, 34 (30%) negative/positive, and 55 (48%) were negative/negative. Approximately 38% of skin test converters were estimated to have boosting. There was a significant non-linear effect of age for ELISPOT results in skin test converters (p = 0.038). Three converters were diagnosed with TB, 2 had ELISPOT results: both were positive, including one at recruitment.

Conclusions: We estimate that approximately 38% of tuberculin skin test conversion in Gambian TB case contacts is due to boosting. This varies with age. Use of ELISPOT only in tuberculin converters may lead to delayed diagnosis of M. tuberculosis infection and disease. Further studies are required to determine the relevance of ELISPOT reversion.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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