Tuberculosis exposure of patients and staff in an outpatient hemodialysis unit.

BACKGROUND: Patients receiving hemodialysis are generally considered to be at increased risk of developing tuberculosis (TB). We evaluated a 13-station chronic outpatient hemodialysis unit associated with a community hospital in northern California. Within 6 months, there were 2 incident source cases in the unit of active smear positive pulmonary tuberculosis; the first in a health care worker (HCW), diagnosed April 3, 1998, and the second in a patient undergoing dialysis treatment in October 1998. We describe the cases; the evaluation of exposures; and the institution of an intentional prospective TB control plan, designed specifically for the unique hemodialysis setting.
METHODS: We evaluated 23 HCWs twice and 89 patients undergoing hemodialysis treatment who were exposed to case 1 and 38 patients who were exposed to case 2. All 23 HCWs had documented prior negative Sierbert purified protein derivative of tuberculin (PPD) status and were retested at 12 weeks after exposure. None of the patients had documentation of PPD status. All of the patients were skin-tested initially with use of the 2-step method, and those with positive test results were offered isoniazid (INH).
RESULTS: One of the 23 HCWs' negative baseline PPD skin test status converted after exposure to case 1, and none of the remaining 22 converted after exposure to case 2. Twelve of 89 exposed patients with no prior skin test record had positive results for PPD after initial testing with the 2-step method. Three of the 12 (25%) patients were treated with INH at the discretion of their attending nephrologist. The 77 patients with negative results for PPD still had negative test results when retested at 3 months. None of 38 patients who underwent dialysis on the same schedule as source case 2 had a converted PPD test. Restriction fragment length polymorphism on TB isolates from both source cases ultimately showed them to be unrelated strains.
CONCLUSION: Our experience with these exposures suggests that TB screening of patient populations undergoing renal dialysis-though they have intrinsic high anergy rates-is advisable with a designed prospective plan before any inadvertent and/or repetitive exposure of that population to active TB. A planned intentional TB control program increases HCW awareness of TB, establishes baselines for evaluation, decreases "panic" in the event of subsequent exposures, and emphasizes the rationale for preventive therapy.