Nurses and Latent TB Infection

Mantoux skin test/CDC PHIL

Are you “PPD positive”?

In December, a California maternity nurse was diagnosed with active tuberculosis. More than 1,000 people, including 350 infants, may have been exposed. In infants, tuberculosis can be hard to diagnose and is more likely than in newly infected adults to progress to active disease and to disseminate to extrapulmonary sites. Therefore, a course of isoniazid was recommended for each of these exposed infants, as well as for any parents, visitors, or staff who tested positive after the exposure.

Some of the details of this incident weren’t released to the media. In my experience, active infection in a health care worker who has not recently traveled to a TB-endemic area is almost always the result of reactivated latent infection. That was the case in a similar exposure more than 10 years ago, when a New York City maternity nurse exposed more than 1,500 infants and adults to active tuberculosis.

And in three of the largest TB exposure investigations on which I’ve worked, the index cases were nurses in oncology, transplant, and the ED whose latent tuberculosis infection progressed to active infection. In these three cases, neither the RNs nor their own primary care providers connected their persistent febrile respiratory infections with their latent TB status.

A positive purified protein derivative (PPD) skin test or TB blood test isn’t simply a benign occupational hazard; it’s an important part of your medical history. For your own safety and that of your family, patients, and coworkers, this information should always be shared with personal health care providers.

While latent disease is most likely to become active within the first two years after infection, many factors can cause later activation, including immunosuppression from drugs or disease, poorly controlled diabetes, certain cancers, chronic renal failure, and malabsorption syndromes, including those precipitated by gastric bypass surgery. The likelihood of reactivation also increases with age.

People with latent TB infection are not immune to new tuberculosis infections. Exogenous reinfection of “PPD-positive” people can occur (and was documented in one of the cases on which I worked). Also, the CDC has made clear that childhood vaccination with bacillus Calmette-Guérin (BCG) is unlikely to protect adults from TB and is unlikely to be the reason for a BCG-vaccinated adult’s positive PPD.

In other words, people from TB-endemic countries who were vaccinated with BCG and find themselves to be PPD positive are almost certain to be latently infected, and not simply falsely positive on skin testing.

When latent TB is treated, it is less likely to progress to active disease. If you are PPD positive, consider prophylactic treatment. Nine months of daily isoniazid is no longer your only option; a newer 12-week regimen that combines isoniazid and rifapentine is possible.

If you are PPD positive, also make sure that your latent TB status is part of the differential diagnosis if you develop persistent cough, fevers, unexplained weight loss, or night sweats that could be symptoms of active disease. For additional information and resources, please see our 2012 article on this subject.