Most commonly, tuberculosis goes through three stages:
Primary TB infectionLatent TB infectionActive TB disease
Millions of people carry latent TB bacteria but never develop active tuberculosis. In fact, the Centers for Disease Control and Prevention (CDC) estimates that as many as 13 million people in the United States have a latent TB infection. (1,2,3) About 30 percent of people who get exposed to Mycobacterium tuberculosis will develop latent TB and, if that’s left untreated, around 5 to 10 percent of those people could end up getting active tuberculosis disease at some point in their lifetime, according to a statement from the US Preventive Services Taskforce, published in September 2016 in the Journal of the American Medical Association. The number is much higher for people infected with HIV. (3,4) Tuberculosis is more likely to enter the active phase in people who have acquired the infection recently (in the past two years). It’s also more likely to be active among those whose immune systems are weakened.
Primary or Initial Tuberculosis Infection
Infection with M. tuberculosis begins when a person breathes in airborne bacteria. This is more likely to happen if a person is in close contact with one or more infected people with active TB who are coughing or sneezing. In many people, any inhaled bacteria are killed immediately by the immune system. In others, the TB bacteria are surrounded by macrophages, a type of white blood cell, and enter a dormant state. This is called latent infection, and this stage can last for years or even for life. But in certain populations, including infants, the elderly, those with recently acquired TB infection, and people with weakened immune systems, symptoms of active tuberculosis may start within weeks of primary infection. (2)
What It Means to Have a Latent TB Infection
While a person with latent TB has no symptoms and is not infectious, a tuberculin skin test or blood test for TB — called the interferon-gamma release assay, or IGRA — will be positive, showing that the person has not only been exposed to tuberculosis, but has a latent (or “occult”) infection with the bacteria that causes tuberculosis. (2,5) “You have a ticking bomb waiting for your immune system to get weak,” says Hayan Yacoub, MD, internal medicine practitioner at Austin Regional Clinic in Texas. Latent TB can also complicate treatment for potential health issues that happen later in life, he says. That’s why it’s important to identify and treat latent TB. If a latent infection is discovered, treatment is recommended in certain individuals at high risk to prevent that person from developing active disease and to prevent the further spread of tuberculosis. People at high risk of TB infection (such as those who work in hospitals) may be screened, sometimes annually, for latent infection.
Who Should Get Tested for Latent Tuberculosis?
In the United States, there isn’t a need to test everyone for Latent TB because it’s unlikely most people will come in contact with someone who has the active disease. “The average person doesn’t get exposed to TB," says Lee Reichman, MD, MPH, professor of medicine and epidemiology and executive director emeritus of the Rutgers Global Tuberculosis Institute in Newark, New Jersey. “For example, if you work in publishing and just go to work and go home, we don’t test you because [exposure] is unlikely.” Screening for latent TB is done based on your risk factors. The following populations should be screened: (6,7)
People who have recently come to the United States from a country with a high rate of tuberculosisPeople whose work or living arrangement puts them in contact with people who have active tuberculosisPeople with other diseases that increase the risk of developing active TB once infected, such as insulin-requiring diabetes, end-stage renal disease, prior gastrectomy, or HIV infectionPeople who are taking drugs that block tumor necrosis factor alpha (TNF-alpha), such as infliximab (Remicade), adalimumab (Humira), or etanercept (Enbrel)
People who plan to start chemotherapy for cancer or an immunosuppressive drug — to treat an autoimmune condition, for example — should also be screened for latent tuberculosis. The risk of a latent TB infection becoming active is much higher in people infected with HIV than those without HIV, according to an article published in February 2016 in the journal Emerging Microbes & Infections. (8)
What Does Treatment for Latent TB Involve?
Treatment for latent TB involves less medication and a shorter regimen than treatment of active TB, says Alexea M. Gaffney-Adams, MD, an internist and pediatrician with a subspecialty training in infectious disease, at Stony Brook Medicine in Smithtown, New York. The most commonly used drug for latent TB is isoniazid (Nydrazid), but it needs to be taken for six to nine months in order to kill the bacteria. (5,9)
What It Means to Have Active Tuberculosis Disease
In active tuberculosis, the bacteria multiply in the body, causing noticeable symptoms. This is also when the disease can spread to others. The difference between active and latent TB is the amount of organisms in the body, according to Dr. Reichman. The most common kind of tuberculosis, pulmonary tuberculosis, typically causes the following symptoms: (5,10)
Breathing difficultyChest painCoughing, sometimes with phlegmFatigueFeverNight sweatsWeaknessWeight lossWheezing
In addition to the lungs, tuberculosis can affect other parts of the body, including the lymph nodes, other internal organs, bones and joints, or the brain. This form of the disease, called extrapulmonary tuberculosis, also causes fatigue, fever, night sweats, weakness, and weight loss, and may also cause other symptoms depending on what body parts are affected. Active TB is curable, but the disease can be deadly if left untreated. About 45 percent of people not infected with HIV, and almost all HIV-positive people, will die from TB without proper treatment. (11) Tuberculosis is spread through the air, which means you can only get it by breathing contaminated air. If someone who is actively sick talks, coughs, sneezes or speaks, they can spread TB. According to the World Health Organization (WHO), people with active TB can infect 10 to 15 other people they come into regular close contact with in the course of a year. (11) The reality is that if someone does have active TB, they’re breathing bacteria out into the air and anyone can pick them up, says Dr. Gaffney-Adams. “You’re most likely to spread it to your household, but it can definitely spread elsewhere.”
Who Should Get Tested for Active TB Disease?
If you find out you’ve been exposed to someone with TB, you need screening, says Gaffney-Adams. If a first screening was negative, she recommends going in for testing again, especially if you experience any respiratory symptoms. The CDC recommends screening anyone with the following symptoms for active TB: (7)
Coughing that lasts for three weeks or longerWeight loss that can’t be explainedCoughing up bloodChest painLoss of appetiteNight sweatsFeverFatigue
According to Gaffney-Adams, who has treated several cases of both latent and active TB, night sweats is a very common symptom in TB. It’s usually pretty dramatic, she says, like sweating so heavily that a person needs to get up and change sheets and clothes.
What Does Treatment for Active TB Involve?
The treatment for any type of active tuberculosis is long-term administration of antibiotics. Because there are so many drug-resistant strains of TB, people with active disease must take more than one antibiotic to ensure that all of the bacteria are killed. In addition, because tuberculosis bacteria grow slowly, it’s necessary to take the antibiotics for at least six months. (5,12) Treatment for active TB will include a combination of three to four of these drugs:
Isoniazid (Nydrazid)Rifampin (Rifadin)PyrazinamideEthambutol (Myambutol)
One major concern in the treatment of active TB is making sure people continue to take the medication even after symptoms have gone away. People typically need to take medication for about a year, so they often get tired of it and forget, says Robert Amler, MD, dean and professor of public health, and professor of pediatrics and environmental health science at New York Medical College in Valhalla, New York. Stopping the drugs early can cause the TB bacteria to return, and that bacteria may not respond to drugs that worked the first time. This is called drug-resistant TB, and it’s much harder to treat. To make sure people with active TB finish the full medication schedule, directly observed therapy, or DOT, is used. In DOT, a trained healthcare worker provides each dose of medication, watches the patient swallow it, and documents that the medication has been taken.
