As TB declines, what is risk to health care workers?

426 infected in 2005, but data inconclusive

For reported tuberculosis cases in the United Sates in 2005 in which the occupation was known, 3.4% were health workers. Though the data were provided by the Centers for Disease Control and Prevention (CDC) upon request, meaningful interpretation of the numbers is another matter entirely.

Unanswered questions include whether the TB cases represent true occupational infections or whether they reflect community acquisition or late onset disease among the foreign-born. According to the CDC data for 2005, the most recent year available, there were 14,097 total TB cases in the United States. Of those, 13,234 TB patients were ages 15 and older. Of those 15 and older, 12,712 had known occupations. Of those with known occupations, 426 (3.4%) were health care workers. The data reflect active infections and skin-test conversions, which signal latent infection that has a 5-10% chance to progress to disease over an immune-competent person's lifetime.

In contrast, the rate of TB in the general population is only 0.2%. "The foreign-born rate last year was just 2.2%, so [the health care worker rate] is similar to rates among the foreign-born," says Paul A. Jensen, PhD, engineering director in the CDC Division of TB Elimination. "Can we say that they are at higher risk? They obviously are if they have TB in their facility, but we can't say all of that TB was acquired in the facility."

While the CDC data are too limited to draw any definitive conclusions, Jenson says the numbers may reflect socioeconomic factors, foreign-born workers, and those of minority status. TB continues to exact its most severe toll among racial and ethnic minorities and foreign-born individuals in the United States, according to the CDC. In 2006, TB rates among blacks and Hispanics (10.1 and 9.2 per 100,000 people, respectively) were approximately eight times the rate among whites (1.2). Asians had the highest rate of any racial/ethnic group (25.6) — more than 21 times the rate for whites. The TB rate among foreign-born people living in the United States was nearly 10 times the rate for those born in the United States (2.3 and 21.9, respectively).

That said, some portion of the numbers likely represent true occupational infections based on analysis of data when TB resurged in hospitals in the early 1990s. "Some of the data from the 1990s show that the people with a lot of patient contact time and then the lesser-skilled people are at higher risk," Jensen says. "Some of those lesser-skilled people are minorities and foreign born. In the subset of health care workers, some of those are at higher risk and some of those [are in at-risk] socioeconomic groups. I agree that [3.4%] is higher than the [national] average but we can't say what proportion of it was occupationally acquired."

A total of 13,767 TB cases were reported in the United States in 2006, down from 14,085 cases in 2005. The 2006 national TB case rate, 4.6 cases per 100,000 people, was the lowest since reporting began in 1953. However, the decline of 3.2% in the national TB case rate from 2005 to 2006 was one of the smallest in more than a decade. "The decrease by year is getting smaller and smaller percentage-wise," Jensen says. "I won't say we've 'bottomed out,' but it's difficult to get much lower levels of TB."

Anecdotally, one would think declining prevalence would translate to less occupational risk for health care workers, but Jensen notes, "There aren't any recent studies to document that. Neither does the CDC have comparative occupational data to assess whether, for example, other job sectors with minority and foreign-born workers have comparable TB rates. TB is a reportable disease, but we don't always get the occupation with it, so that is a limiting factor," he says. The take-home point, however, is once the full cadre of CDC TB controls is in place in a hospital, skin-test conversions among health care workers drop dramatically. As an example, Jensen cites Grady Memorial Hospital in Atlanta, which was hit hard in the 1990s but now has virtually eliminated TB transmission within its doors. "They have more TB [patients] in their hospital than some states have, but they have relatively low rates among their staff," he says.