Tuberculosis: Risk Factors, Causes, and Prevention

Tuberculosis can be prevented by knowing how the infection spreads and what puts someone at a higher risk for the disease.

Mycobacterium tuberculosisis spread from person to person when someone with an active form of tuberculosis (TB) emits tiny, bacteria-containing droplets into the air through coughing, sneezing, talking, singing, or laughing. The bacteria can remain suspended in the air for hours, potentially infecting anyone who breathes them in. (1,2)

When a patient who has never been exposed to TB inhales the bacteria, it results in an initial TB infection, or primary infection. At this stage, some people have no symptoms, while others may experience fever or pulmonary symptoms.

In most people who’ve inhaled the bacteria, the immune system immediately kicks in and you recover without further signs of the disease. Or the bacteria may then remain in a latent, or dormant, state — it's in your system, but not making you sick. But in some cases, the bacteria eventually reactivate and multiply, leading to the active form of TB — when it makes the person symptomatic and contagious. (3)

Latent TB shouldn’t be ignored, though, because the disease can become active at any time if your immune system gets weakened. According to the Centers for Disease Control and Prevention (CDC), about 5 to 10 percent of people infected with latent TB develop active TB at some point in their lives if they don’t receive treatment. (4)

Each stage doesn’t necessarily have to lead to the next, according toAsim A. Jani, MD,a hospital epidemiologist based in Orlando, Florida.

“This results in at least three levels of prevention,” he says.

1. Avoiding initial exposure to places and people at high risk of having TB helps to prevent TB infection.
2. Giving specific prophylactic TB medication to people who have been exposed and are also infected with latent TB can reduce the roughly 10 percent lifetime risk of developing the actual disease to less than 1 percent.
3. Treating the active disease not only helps the person affected, but also helps prevent transmission to others.

What Are the Risk Factors for Getting Tuberculosis?

Risk factors for tuberculosis include anything that weakens a person's immune system or puts someone in frequent, close contact with a person who has active TB. (1,4,5,6)

在美国,你会更喜欢ely to get TB if you travel to or have emigrated from a country with high rates of tuberculosis. Certain populations are at a higher risk because their immune systems are weaker.

More than 95 percent of TB deaths happen in low and middle-income countries, according to the World Health Organization (WHO). Areas of the world with higher rates of tuberculosis include: (1,7)

• Africa
• Asia
• Eastern Europe
• Russia
• Latin America
• Caribbean Islands

These eight countries made up two-thirds of new TB cases in 2017: (7)

• India
• Indonesia
• China
• Philippines
• Pakistan
• Bangladesh
• Nigeria
• South Africa

Robert Amler, MD, dean of the School of Health Sciences and Practice and vice president for government affairs at New York Medical College in Valhalla, New York, recommends visiting theCDC's Traveler’s Health websitefor updates on tuberculosis and other infectious diseases before you travel abroad.

Some of the main risk factors for tuberculosis include: (1,4,5,6,8)

• PovertyPeople living in poverty often lack access to quality healthcare. It’s also possible that in the United States, people with little means could be living close to those who have recently emigrated from a country where TB is common. (1)
• HIV InfectionBecauseHIVattacks the immune system, it puts people at greater risk of getting sick from other bacteria and viruses. The combination of HIV and TB can be especially deadly because the two diseases feed off each other. In 2017, about 300,000people with HIVdied of TB, worldwide. (7)
• HomelessnessPeople who are homeless often live in crowded conditions with little or no access to healthcare.
• Being in Jail or PrisonIncarcerated people are often in enclosed areas with a crowd, breathing the same air.
• Substance AbuseIntravenous (IV) drug use andalcoholismweaken the immune system.
• Taking Medication That Weakens the Immune SystemAutoimmune disorders, likerheumatoid arthritis,psoriasis, andCrohn's disease, cause the body’s immune system to attack itself. Treatments for these disorders often involve medication that suppresses the immune system. But that means your immune system may not be able to fight off TB after exposure. (6)
• Kidney Disease and DiabetesChronic conditions, likekidney diseaseanddiabetes, weaken your immune system, making it harder for the body to fight of TB.
• Organ TransplantsThe drugs people take to prevent the rejection of an organ transplant can weaken the immune system.
• Working in HealthcareDoctors, nurses, and other healthcare workers get exposed to lots of patients on a regular basis, which means they’re also more likely to be close to someone with tuberculosis.
• CancerChemotherapyweakens the immune system.
• Smoking TobaccoSmoking can increase your risk of getting TB and dying from it. The WHO estimates 8 percent of TB cases worldwide can be linked to smoking. (1,7)
• Babies, Young Children, and Elderly PeopleThe immune system can be more vulnerable when someone is very young or very old.

How to Prevent the Spread of Tuberculosis

一般来说,最好的方法预防结核病s to keep your immune system healthy and avoid getting exposed to someone with active TB.

Throughout history, general improvements in health andhygienehave shown drastic reductions in TB cases, saysHayan Yacoub, MD, internal medicine practitioner at Austin Regional Clinic in Texas. Dr. Yacoub has treated people with latent TB at his practice. As a safeguard against TB, he recommends eating healthy and exercising to keep your immune system strong.

“Not everyone ends up with TB or latent TB because your immune system can fight it off,” says Yacoub.

Another big part of preventing new tuberculosis cases isidentifying and treating前潜伏性结核病患者可以变得e active, especially in high-risk populations. If latent TB is treated properly, the bacteria can be killed before it multiplies, making the person sick and infectious.

To prevent thetransmission of tuberculosisin healthcare settings, the CDC has issued guidelines that require most employees to bescreened for tuberculosiswhen they’re hired and then again on a regular, often annual, basis. The testing frequency will depend on the worker’s likelihood of being exposed to TB. (9)

Some residential institutions, such as nursing homes, also screen all new residents for tuberculosis.

Screening for active TB is best accomplished by a chestX-ray.

Some other steps toward preventing the spread of TB include:

• Improving ventilation in indoor spaces so there are fewer bacteria in the air
• Using germicidal ultraviolet lamps to kill airborne bacteria in buildings where people at high risk of tuberculosis live or congregate
• Treating latent infection before it becomes active
• Usingdirectly observed therapy(DOT), in which people taking medication for TB are monitored by their healthcare providers, to raise the likelihood of successful treatment

Long flights, like those lasting 8 hours or more, give you more time to breathe in infectious material from other people’s lungs, says Dr. Amler. If you’re traveling to parts of the world where there are a lot of crowded, enclosed environments, Amler suggests talking to your doctor about screenings when you return.

How Effective Is the Tuberculosis Vaccine?

A vaccine for tuberculosis called bacille Calmette-Guérin, or BCG, has been around since the 1920s. It was created from a weaker strain of theMycobacterium bovisbacteria, a version of tuberculosis that affects cows. It’s used in parts of the world with high rates of the infection to prevent serious complications, likemeningitis, which is common in young children. (10,11)

But BCG is rarely used in the United States because some studies have shown that BCG is not very effective in preventing TB cases, and because treatment oflatent TB infectionwithisoniazidis a more effective prevention strategy. (10)

People who might benefit from BCG are children or healthcare workers constantly being exposed to others with an active infection. Typically, doctors would only recommend a child get the vaccine if they live with an adult who has active TB and are unable to take the antibiotics needed to treat TB, or if the adult has a strain of TB that’s resistant to antibiotics. (10,11)