periods had infection traceable to their stay on the ward during those periods. When workers on the HIV ward were compared to workers on a control ward that did not admit HIV infected patients, the former group had significantly higher skin test conversions rates during the outbreak period from January 1988 through January 1990 (Beck-Sague et al., 1992). Rates for the two groups of health care workers did not differ significantly for the period from June 1990 through June 1992 (Wenger et al., 1995).

The study authors note that although the “density” of patients with multidrug-resistant disease declined after the initial monitoring period, “infectious patients were still present and the potential for transmission still existed” (p. 239). Indeed, two of the three skin test conversions in the follow-up period occurred in workers who were exposed to a patient who had previously been diagnosed with tuberculosis but who was thought to be no longer infectious. This led to a requirement that all patients with multidrug-resistant tuberculosis be isolated upon admission. Following the implementation of this policy, no further tuberculin skin test conversions were reported among health care workers. The study authors concluded that most of the effect of the controls came before complete implementation of the engineering controls and respiratory protections and, thus, were likely due to administrative controls.

Cabrini Medical Center (New York City) Another report following an outbreak of multidrug-resistant tuberculosis tracked the sequential adoption of tuberculosis control measures from June through October 1991 (Maloney et al., 1995). The control measures included stricter isolation criteria and use of molded surgical masks for employees (June), improved laboratory services (July), increase from no isolation rooms (0 of 10) with negative pressure to a majority of rooms (16 of 27) with negative pressure (September), and use of an isolation chamber for sputum induction and administration of inhaled pentamidine (October).

The initial assessment of worker tuberculin skin test conversions found similar conversions rates during the preintervention period (January 1990 to June 1991) and the intervention period (July 1991 through August 1992). When the analysts categorized workers by job category and ward location, however, they found higher conversion rates during the 18-month preintervention period for workers on wards serving tuberculosis patients than for workers on other wards (16.7 versus 2.8 percent). In contrast, during the 13-month intervention period, rates for the comparison groups differed little (5.1 versus 4.0 percent). When analysts categorized workers by whether or not they had direct patient contact, the difference in rates was smaller for the preintervention period (6.4 percent for those with patient contact and 1.0 percent for those without patient contact) and the change during the intervention period was less (4.7 percent

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