High rate of tuberculin conversion in Indochinese refugees.

From January 1979 through December 1980, a total of 664 Indochinese refugees were screened for tuberculosis in Monroe County, New York; 307 (46%) had positive 5-tuberculin unit PPD Mantoux tests. When 217 refugees with initially negative tests were retested at 60 days, 94 (43%) had converted from a negative to a positive test. Although none of the converters had evidence of active tuberculosis disease, 90 (96%) were given isoniazid preventive therapy. This conversion phenomenon has continued over time, discounting an effect of local, national, or international policy changes. The conversions do not seem to be a function of antigen, tester, or reader; criteria for testing, retesting, or reading; home country, camp country, or length of time in camp; or history of prior BCG vaccination, tuberculosis, or immunization exposure, current illness, or testing intervals since arrival in the United States and subsequent testing. Further studies to evaluate boosting or anergy are in progress to assess this potential public health problem.