For the 13-month period from June 1991 through August 1992, the difference in conversion rates for the more exposed and the less exposed groups of workers had narrowed to a nonsignificant 5.1 versus 4.0 percent respectively. The researchers did not find that conversion rates correlated with zip code of residence, race, or other demographic characteristics. Again, the investigators documented lapses in infection control measures.
At Grady Memorial Hospital in Atlanta, hospital staff tracked skin test conversion rates after an outbreak of tuberculosis and the implementation of infection control measures (Blumberg et al., 1995; Sotir et al., 1997).7 In the first period studied, January through June 1992, 3.3 percent (annual rate, 6.49 percent) of workers with previous negative skin tests converted. For January through June 1994, the conversion rate had dropped to 0.4 percent (annual rate, 0.89 percent).
A later report focused on house staff, who served in hospitals affiliated with Emory University and typically spent about half their training at Grady Memorial Hospital (Blumberg et al., 1998). Over the study period, skin test conversion rates dropped from approximately 6.0 per 100 person-years to 1.1 after implementation of expanded tuberculosis control measures. Over the entire period studied, house officers in the medicine and obstetrics/gynecology departments had significantly higher skin test conversion rates than house officers in other departments, but the rates for the groups were not significantly different by the end of the study period. Graduates of foreign medical schools had much higher conversion rates than graduates of U.S. medical schools. Throughout the study period the house staff continued to care for large numbers of patients with active tuberculosis.
Some workplace investigations have used DNA fingerprinting in an effort to assess the likelihood of a workplace rather than community source of transmission. Some have concluded that transmission of M. tuberculosis to health care workers resulted from workplace sources.
Of the outbreak reports that the committee found on organizations other than hospitals, most involve correctional facilities. The reports, however, often focus on inmates rather than correctional facility workers.
Prisons Three studies have reported on outbreaks in California prisons that involved the transmission of M. tuberculosis from inmates to correctional facility personnel. For one 1990–1991 outbreak, the skin test