Epidemiology and Infection

Original Papers

Tuberculosis

Estimation of incidence of tuberculosis infection in health-care workers using repeated interferon-γ assays

T. YOSHIYAMAa1 c1, N. HARADAa2, K. HIGUCHIa2, Y. NAKAJIMAa3 and H. OGATAa1

a1 Fukujuji Hospital, Matsuyama, Kiyose, Tokyo, Japan

a2 Research Institute of Tuberculosis, Matsuyama, Kiyose, Tokyo, Japan

a3 NHO Tokyo Hospital, Takeoka, Kiyose, Tokyo, Japan

SUMMARY

The aim was to estimate the incidence of Mycobacterium tuberculosis (Mtb) infection in health-care workers (HCWs) in Japan. We repeated cross-sectional surveys of HCWs with QuantiFERON®-TB Gold (QFT-G) in 2003, 2005 and 2007 at a hospital with tuberculosis (TB) wards, and 311 HCWs who underwent QFT-G testing two or three times were included in the study. Five HCWs (1·8%) converted from negative to positive. Incidence of new TB infection was estimated to be 0·6/100 person-years by the CDC's definition. Thirteen positive persons (41%) reverted from positive to negative. Multivariable logistic regression analysis identified a significant association between QFT-G conversion and working in TB wards. The IFN-γ levels of all but two subjects with reverting or converting QFT-G results were close to the test's cut-off. The incidence of Mtb infection in HCWs at our hospital was higher than that estimated for the general population in Japan. Criteria for defining QFT-G conversion and reversion need further investigation considering the high proportion of reversion, as the incidence of infection would have changed if we had applied other definitions.

(Accepted April 12 2009)

(Online publication May 11 2009)

Correspondence:

c1 Author for correspondence: T. Yoshiyama, M.D., c/o Fukujuji Hospital, 3-1-24 Matsuyama, Kiyose, Tokyo, Japan. (Email: yoshiyama1962@yahoo.co.jp)

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