guidelines for the prevention of transmission of tuberculosis in health care facilities. OSHA published a proposed rule on occupational tuberculosis in 1997 and solicited comments on the rule in 1998 and again in 1999. In addition, some state licensure agencies and private accrediting organizations required tuberculosis control measures.

Decreasing Rates of Disease

The epidemiology of tuberculosis has changed substantially since the early 1990s. In 1993, the trend of increasing tuberculosis case rates began to reverse, and declines have now been recorded for 7 successive years. Tuberculosis case rates reached new lows in 1999, when CDC reported a rate of 6.4 per 100,000 population, a 35 percent drop since 1992. Cases of multidrug-resistant disease have also decreased; in 1999, they accounted for just 1.2 percent of cases. In general, fewer cases of tuberculosis and less multidrug-resistant disease mean less risk for nurses, doctors, correctional officers, and others who work for organizations that serve people who have tuberculosis or who are at increased risk of the disease.

Continuing Geographic Variation

Despite the general decline in tuberculosis rates in recent years, a marked geographic variation in tuberculosis case rates persists, which means that workers in different areas face different potential risks. Among metropolitan statistical areas, 1999 case rates varied from 1.3 per 100,000 population in Omaha to 17.7 per 100,000 in New York City and 18.2 per 100,000 in San Francisco. Between 1994 and 1998, six states—California, Florida, Illinois, New Jersey, New York, and Texas—accounted for 57 percent of tuberculosis cases but had just under 40 percent of the U.S. population. These states also account for a large proportion of people with risk factors for the disease, notably, HIV infection and immigration from countries with a high prevalence of tuberculosis. More than 40 percent of tuberculosis cases reported in the United States in 1999 involved people born in other countries, primarily Mexico, the Philippines, and Vietnam.

Conclusions

One problem facing the IOM committee as well as CDC and OSHA was the lack of prospective, controlled studies documenting the effectiveness of specific protective measures in preventing the transmission of tuberculosis in the workplace. Most studies of these protective measures are retrospective or observational, and they are inconsistent in their methods and reporting. The studies typically involve organiza-



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