519. Higher than Expected Annual QuantiFERON-Gold (QFT-G "Conversion" Rate Suggests Need for Redfining Reactivity Criteria in Health Care Workers (HCWs)
Session: Poster Session: Hospital-acquired and Transplant Infections
Friday, October 30, 2009: 12:00 AM
Room: Poster Hall A
Background: HCWs at risk of exposure to TB are tested at least annually. Traditionally, this testing was done with TSTs. Now that IGRA testing has become available, some facilities are using this methodology. At MSKCC, we still use the TST for previously negative HCWs, but since 5/1/08, we have been using QFT-G for annual testing of those who previously received BCG and were initially TST-positive, but QFT-G-negative. We found a “conversion” rate well in excess of our past experience. The significance of this remains to be determined.
Methods: The medical records of all HCW’s who underwent QFT-G screening at least two years (5/1/07-4/30/08) in succession were reviewed to distinguish the characteristics of those who remained consistently negative from those who were initially identified as negative, but on at least one subsequent test, were positive.
Results: 170 HCWs fulfilled the criteria noted above. 15 (8.8%) of these HCWs “converted” from negative (< 0.35) to positive ( > 0.35) results during the 12 month interval. In contrast, the annual TST conversion rate in our hospital has ranged from 0.05% to 0.3% over the past 4 years and was 0.05% among those HCWs screened by TST during the year from 5/1/08 - 4/30/09. The baseline QFT-G for all “converters” had differences between the nil value and the most elevated antigen (ESAT-6 or CFP-10) value of at least 0.10, with a single exception. In contrast, only 11/155 (7.0%) of the HCW’s who remained consistently negative had differences exceeding 0.09. All of those who “converted” always did so to the same antigen to which they had responded as negatives. Moreover, 3 of the 15 “converters”, when retested, reverted to a negative result.
Conclusions: It is unlikely that those HCWs identified as QFT-G “converters” reflect a true change in their status. Rather, it is possible that the original QFT-G, known to be a less sensitive test than it is specific, may have failed to identify HCW’s with latent tuberculosis infection (LTBI). Should this observation be confirmed, it may be argued that different criteria may be needed for the diagnosis of LTBI in HCWs.
Arthur Brown, MD1, Cynthia Eisenstein, RN2, William Schneider, MD, MPH2 and  W. J. Schneider,
HYSO Role(s): Other, Received: Other Financial Benefit.
C. Eisenstein, None..
A. E. Brown, None., (1)Memorial Sloan Kettering Cancer Center, New York, NY, (2)Memorial Sloan-Kettering Cancer Center, New York, NY