A little-known form of “sleeping” tuberculosis (TB) that affects millions of Americans is making headlines after a local outbreak at a San Francisco school. The spate of cases is a reminder that sleeping doesn’t mean safe.
The San Francisco Department of Public Health declared a TB outbreak at San Francisco’s Archbishop Riordan High School in late January, sparking concern from parents and city residents. The announcement came after the department diagnosed and began treating three people from the school with active TB disease.
In the wake of the announcement, the city also identified more than 50 people with latent TB infection — an overlooked form of TB.
Priya Shete, MD, MPH, associate professor of medicine and epidemiology at UC San Francisco and co-director of the UCSF Center for Tuberculosis, explains what latent TB is, the health risks, and what residents should know.
What is active TB?
Globally, TB is the world’s leading infectious disease killer and is responsible for about 1.2 million deaths annually. Active TB is an infectious disease caused by bacteria that spreads through airborne droplets released when people with active TB in their lungs cough, sneeze, or speak.
When people have active TB, they can develop symptoms, including:
- Cough lasting three weeks or more
- Unexplained weight loss
- A loss of appetite
- Night sweats
- Fevers
Active TB can cause pneumonia, respiratory distress and can be fatal if untreated. Active TB can be spread. Fortunately, it can also be diagnosed and treated, and most importantly, prevented.
What is latent TB?
Latent TB is when a person has been infected with the tuberculosis bacteria, but the bacteria are dormant, or “asleep,” because the immune system has figured out how to keep it in check.
Can latent TB be transmitted?
No. People with latent TB generally feel fine — nothing shows up on a chest x-ray, for example, and they don’t have symptoms like a cough, which also means they can’t spread the germ to others.
Why worry about latent TB?
Latent TB can “wake up,” and cause active TB disease. Up to 13 million Americans are estimated to have latent TB, although only around 10,000 develop TB disease each year. Still, without treatment, it can be deadly; in San Francisco, 1 in 10 people who have active TB die of the disease.
Which tests can detect latent TB?
There are two types of tests for latent TB. There’s a skin-prick test in which a health care provider will lightly prick the skin with a harmless testing solution. Forty-eight or 72 hours later, you’ll go back and have the site checked for a reaction. Generally, it’s a pretty good way of testing for latent TB, but it’s not perfect, and how to interpret the result depends on other health conditions.
There’s also a blood test, which we generally recommend because it’s more accurate in detecting latent TB than the skin test.
How is latent TB treated?
Once health care providers exclude active TB disease, people with latent TB are eligible for TB preventative therapy, which can range from three months of once-weekly treatment to four months of daily pills.
In most cases, once you finish with that, the risk of developing active TB is negligible.
We highly recommend — especially in cases where there has been a recent outbreak or recent transmission — to go ahead and take that therapy if you do have latent TB, because you want to get ahead of it as fast as possible to prevent active TB.
Treating latent TB keeps people healthy and reduces transmission, but your research has found major gaps in testing and treatment in the U.S. Why?
There are a few reasons. For one, it’s always challenging to get otherwise healthy people to test and take medication for something that’s not bothering them. This is especially hard when it’s for a disease like TB that is not generally as big a problem in the U.S. as in other parts of the world.
It can also be hard for primary care providers to address during visits where there are competing concerns to address, such as diabetes and hypertension.
Finally, we’ve found that our health systems are not set up to easily help providers identify who may be at risk for TB by screening them, and there are no quality measures in place yet to make sure that we do.
How has your research contributed to new regulations to keep Californians healthy?
Our research has shown that one of the biggest gaps in preventing TB in the U.S. is getting people who are at risk screened and tested. Without this early step in care, we can’t get people who need it on preventative treatment.
I’m really proud that, knowing all this, California passed Assembly Bill 2132 last year that mandates that primary care providers offer screening and testing for latent TB infection to anyone at risk for TB. This law has the potential for really making latent TB screening and testing a part of standard primary care practice for everyone.
The challenge is that there’s no “teeth”: clinicians who are unable to do this aren’t penalized, especially if a patient’s health insurance doesn’t cover it.
Does insurance cover latent TB treatment?
In California, Medi-Cal, Medicare, and other health insurance usually covers testing for latent TB infection for people who are considered at higher risk. That includes people with weaker immune systems, those born in countries where TB is common, or people who work or live in high-risk settings. Our center helped draft a formal request to the Centers for Medicare & Medicaid to expand this nationwide.
How else is UCSF’s research helping fight TB at home and abroad?
I can’t think of an area of TB research and innovation where UCSF isn’t involved — from our work improving California’s TB prevention systems to designing better rapid tests that enable people to start treatment as early as possible to creating shorter TB treatment regimens. We’re also among the first to investigate TB’s long-lasting impacts on a person’s health even after they are cured. And we’re coming into an era in which we hope an effective, long-lasting TB vaccine could be closer than ever.
Funding for this science has been crucial in supporting the fight against TB. National Institutes of Health funding has, for instance, allowed UCSF and UC Berkeley to jointly become a national center of excellence as part of the UC TB Research Advancement Center.