Two-Stage Skin Testing for Tuberculosis in a Domiciliary Population

Abstract

We scheduled two-stage skin testing for tuberculosis with Candida and mumps controls on 618 residents of our domiciliary unit at the Veterans Administration Medical Center, Johnson City, Tennessee. Of the 618 residents in the unit, 30 (4.8%) were not available for evaluation, 77 (13%) had a prior history of active tuberculosis or positive skin test, and 1 resident refused testing. Of these 510 patients who received first-step testing with purified protein derivative (PPD), 153 (30%) had greater than to 10 mm induration. Those patients with less than 10 mm induration had a repeat PPD 2 wk later. Fifty-nine (19.2%) of the 307 patients who received a second PPD had a booster response. A total of 50.9% of the residents had evidence of tuberculosis exposure by skin testing. There were no differences between patients with significant and nonsignificant reactions when comparing age, length of stay, functional status evaluated by Karnofsky scale, or number of underlying diseases. Second test conversion occurred in 4.3% of those patients who had been in the unit for less than 1 month and in 36% of those who had been residents for a period of 3 to 6 months (p less than 0.05). Regardless of the size of the initial reading, it is important to perform a two-stage PPD in residents of chronic care facilities who have a negative first test. INH prophylaxis should be considered in patients admitted to chronic care facilities such as the domiciliary when they have significant Mantoux reactions.