Abstract
Rationale: The role of two stage tuberculin skin test (TST) of persons who have had close contact with a case of smear-or culture positive pulmonary tuberculosis TB (PTB) is unclear. A booster phenomenon with TST may occur and therefore screening with TST in a two stage approach may not be ideal [1].
Methods: We conducted a prospective study including consecutive household contacts of patients with active PTB between Jan 2010 and Jan 2011. All contacts below the age of 35 years of age were interviewed and screened by TST. If the TST was below 6mm, contacts were asked to return for a second TST six weeks later. TST conversion was defined as a TST of greater than 6mm or a 5mm increase of the initial TST. Interferon Gamma Recptor Assay (IGRA), (T-spot test) was performed on those that had TST conversion to evaluate the booster phenomenon.
Results: Out of 589 adult and peadiatric contacts screened who had an initial TST of less than 6 mm, 189 contacts did not attend for a second TST. A total of 406 had TST performed. 344 contacts attended and did not show TST conversion and were therefore discharged. 68 contacts underwent TST conversion of whom 43 had an IGRA. Out of 43 contacts, 6 had a positive IGRA, 7 out of 43 were indeterminate and 30 were negative. Indeterminate and negative IGRA results were more common in children than in adults.
Conclusion: A two stage approach of TST may cause a booster effect and therefore should be confirmed by IGRA.
Reference:
1. Menzies D. Interpretation of repeated tuberculin tests. Boosting, conversion, and reversion. Am.J.Respir.Crit Care Med. 1999;159:15-21.
- © 2011 ERS
