Tuberculosis (TB): Progression of the Disease, Latent and Active Infections.
Could You Have TB and Not Know It?
Millions may be infected with latent tuberculosis and not know it, but how dangerous is the infection? Find out the difference between TB infection and active disease.
By Jennifer Warner
Medically Reviewed by Rosalyn Carson-DeWitt, MD
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You might think you’d know if you had a disease as serious as tuberculosis (TB), but that’s not necessarily the case.
Nearly one third of the world’s population — about 2.3 billion people — is infected with TB, according to the Centers for Disease Control and Prevention (CDC), but many may not know it. In fact, the vast majority of people infected with TB will never get sick — they won’t experience symptoms or become infectious. It’s a condition known as latent tuberculosis, in which the bacteria that cause TB simply stay dormant in the body.
In about 5 to 10 percent of people infected with TB, the bacteria will become active. People with active TB will experience symptoms and can spread TB to others. Nearly 1.5 million people die from TB every year, usually in underdeveloped countries, according to the CDC.
TB is caused by a type of bacteria calledMycobacterium tuberculosis, which can travel in droplets or mucus emitted in the air when a person with active TB coughs, sneezes, speaks, or sings. People nearby who breathe in the bacteria can become infected. TB is usually spread only with very close contact, commonly between family members, but sometimes among the co-workers and healthcare providers taking care of an infected person.
In addition to being in contact with a person who has active TB, other risk factors for TB infection include:
- HIV infection, diabetes, certain cancers, and other conditions that weaken the immune system
- Traveling to, living in, or immigrating from areas of the world with high rates of TB, including Latin America, Africa, Asia, and Russia
- Living or working in a location where TB is more common, including prisons, homeless shelters, immigration centers, nursing homes, and healthcare facilities
- Substance abuse
RELATED: Preventing the Spread of Tuberculosis Infection
Having the infection but not active disease is called latent TB. With latent TB, the bacteria resides in the body as though it's sleeping, explains Eric Rubin, MD, PhD, a professor of immunology and infectious diseases at the Harvard School of Public Health. However, the bacteria can be reactivated, or awakened. In that case, the infected person develops active TB, which causes symptoms and causes the person to become contagious. Active TB is more likely to develop in people who became infected within the past two years.
In active TB the bacteria multiply in the body and usually attack lung tissue, though they can also damage the kidneys, spine, and brain. Symptoms of TB include a bad cough that lasts three weeks or longer, chest pain, a cough that brings up blood or sputum (a mix of saliva and mucus), chills, fever, and night sweats.
The only way to know if you've been infected with TB is to get a skin or blood test.
The Risks of Latent Tuberculosis
Latent TB poses special risks for people with weakened immune systems. That's because an immune system that's compromised — whether because of another disease, such as HIV or diabetes, or from drug or alcohol abuse — may not be able to fight off the bacteria, making it more likely that active TB will develop.
The elderly and infants are also more likely to develop active disease if they become infected with TB because their immune systems aren't as strong as those of healthy adults.
The CDC recommends that people who test positive for TB after exposure receive treatment with a long-term course of antibiotics to reduce the chance of developing the active disease. Active disease itself must be treated aggressively. Without the right treatment, TB can be fatal.
But just how serious a risk is TB for Americans? The CDC's most recent statistics show 9,421 cases in the country in 2014, the lowest number since national tracking began in 1953.
“It’s associated primarily with immigrants, because they were exposed in their home countries,” Rubin says. According to the CDC, two-thirds of the reported TB cases in 2014 were among people born abroad.
“There is not much TB transmission in this country, so there is not a lot of latent disease," he says.
Video: Tuberculosis - causes, symptoms, diagnosis, treatment & pathology
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