compared with 2.3 percent). Analysts examined worker age, race, and BCG vaccination status and concluded that these factors could not account for the differences in skin test conversion rates. They also found no clustering of conversions by the worker’s zip code of residence. The analysts concluded that “the combination of source and environmental controls together with the use of molded surgical masks were all effective in reducing tuberculin skin test conversions among health care workers” (p. 94). The individual effects of different measures could not be isolated.

Other New York City Studies Three additional studies in different New York City hospitals also suggest the effectiveness of tuberculosis control measures. The first report (from Roosevelt Hospital) had insufficient data to analyze skin test conversions for workers (Stroud et al., 1995). For patients, it concluded that the implementation of stricter isolation policies was associated with reduced delays in initiating isolation and reduced rates of patient-to-patient transmission of tuberculosis.

In a second study at St. Clare’s Hospital, analysts reported decreases in skin test conversions for medical house staff concurrent with the adoption of more stringent isolation policies, the initial installation of negative-pressure isolation rooms, and adoption of a new kind of respirator. The conversion rates fell from 20.7 percent for the 6-month preintervention period to 7 percent during the next 6 months (Fella et al., 1995). Subsequent adoption of particulate and then dust-mist-fume respirators was not associated with any further consistent pattern of decreases in conversion rates. The report did not include information on employee demographics. The study’s authors commented that they had a steady inflow of new workers with negative tuberculin skin tests, so “we do not think that our decrease in [tuberculin skin test] conversions is simply the result of an exhaustion of susceptible persons” (Fella et al., 1995, p. 355). However, given inadequacies in the previous skin testing program it was possible that there was “a backlog of 2 years of conversions” in the 20.7 percent rate reported for the first period studied (Fella et al., 1995, p. 355).

A third study at Columbia-Presbyterian Medical Center of the sequential adoption of stricter tuberculosis control measures examined skin test conversions for medical house staff from June 1992 to June 1994 (Bangsberg et al., 1997). The largest drop (from 5.1 to 0 conversions per 100 person-years) occurred after the adoption of a more rigorous isolation policy (administrative controls) and the construction of isolation rooms in the emergency department (engineering controls). This drop occurred before the adoption of new respiratory protections. The number of tuberculosis patients seen remained steady. The authors conclude that stricter isolation policies contribute the most to decreases in skin test conversion rates. They did not report information on employee demographics.

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