Back in the early 1800s, one in seven Americans died from tuberculosis – an infectious disease known as TB for short.

While TB is still one of the top 10 causes of death worldwide, it’s now almost unheard of in the United States. That’s thanks to a longtime national campaign to fight the disease with antibiotics.

Currently, TB rates are so low in the United States that less than 0.1 percent of our population become contagious each year. Yet in September 2016, an individual in St. Louis Park, Minn. was one of those minute few.

So what exactly is TB? And how could it have popped up in suburban Minneapolis – despite seeming virtually non-existent across the country?

Omobosola Akinsete, MD, MPH, MBBS, chair of the HealthPartners infectious disease department, explains.

How do people get infected with tuberculosis? Where can they pick it up?

Dr. Akinsete: You rarely hear about tuberculosis in the United States because we have so few contagious cases of it. But 11 million people in this country have what we call “latent” TB. This means that they picked up the bacteria sometime in their life, but their body’s immune system contained it with scar tissue. So they’re not contagious and they have no symptoms. Most of the time, these people have no idea they were or are infected. In fact, 90 percent of people with latent TB will live their lives without ever feeling sick from it.

However, for 10 percent of people infected, the virus will reactivate later in life. It reactivates when their immune system dips, which can happen for many different reasons. And this is when they start to show symptoms. TB can reactivate in their lungs, which is where it becomes most contagious. But it can also reactivate in the lymph nodes, bones, abdomen, brain and other parts of the body.

So, it’s possible that the individual in St. Louis Park had had latent TB for many years. There’s really no saying where he or she originally got infected.

Once TB is contagious, what are the symptoms?

Dr. Akinsete: The symptoms that a person has when they’re contagious are pretty nonspecific. People talk about a bloody cough, but that doesn’t show up until late. It happens when the bacteria moves into the blood vessels in the lungs. A person would have been contagious for several weeks or even months before then.

The disease starts off with a persistent cough. In the first week or two, it can be so mild that another person wouldn’t even notice something was wrong. The cough could also easily be mistaken for a cold or virus. Oftentimes these early symptoms won’t be enough to cause someone to go see their doctor. But a person’s cough doesn’t go away with TB. And soon they start to have a fever and body aches. Then symptoms get even more severe with the person having night sweats and unexplained weight loss. People tend to finally visit their doctor because they’ve been sick for a long time and their illness keeps getting worse.

Is it standard medical practice to get vaccinated against TB?

Dr. Akinsete: In the United States, no. There is a vaccine that’s often given to children in developing countries where tuberculosis rates are high. However, it’s only about 80 percent effective when given to newborns. And it’s only about 50 percent effective when given to older individuals. Plus, when it is effective, it only protects a person for 15 years at most. For these reasons it is very rarely given to people in the United States. Here, the risk of being harmed by an effect of the vaccine is actually higher than the risk of being infected with TB.

If an individual has contagious TB, how big of a risk for infection is there to the greater community?

Dr. Akinsete: In order to pick up TB, you need to have very, very close contact with someone who is contagious. Most of the time, people who are infected are household members. Or they are in health care and working directly with infected patients. But the people who come in contact with a contagious person in a setting like a classroom usually won’t be infected.

TB survives in droplets. So once it gets coughed up into the air, it gets diluted. That makes it less likely to get passed to someone else. In order to get infected, a person would have to be very close to the face of a contagious individual who was coughing. Or, they would have to be in the same room as the individual for a very long period of time. And that room would have to have very little air circulation. So if a contagious individual has a close friend that he or she is always with and often coughing toward, that friend would be at higher risk. People with weakened immune systems are also at higher risk for picking up the disease. People going through chemotherapy for cancer or those with diabetes, kidney disease or HIV would all fall into this group. If these individuals are infected, they are more likely to be contagious since their bodies can’t easily contain the bacteria.

There are two screening tests available to see if someone at risk for tuberculosis has indeed developed latent TB. One is a skin test. The other is a blood test. It takes less than a week to get results for both.

People who work in HealthPartners hospitals are screened yearly. Their close contact with patients puts them at higher risk for being infected. Many prisons also regularly screen inmates since they live in such close quarters with each other. And all refugees – although not necessarily all immigrants – are tested when they come into the United States as well.

Can someone with TB be cured?

Dr. Akinsete: Yes. People who have active TB can be treated and cured. And so can people with latent TB.

If a person has contagious tuberculosis, they need to be isolated from other people until they’re no longer at risk of spreading the disease. During this time, they need to be treated with at least three medicines. This is because TB is a bacteria that can develop resistance. One antibiotic is not enough. For six months, a health professional keeps close tabs on the person to ensure they are taking their medicines daily. Missed doses could lead to a resistant strain of the bacteria developing. And that could lead to a more infectious and contagious disease.

If a person has latent TB, it can also be eliminated from their system. This gets rid of the chance that it reactivates later and becomes contagious. One antibiotic is enough to treat it. A pill that’s taken at home daily for nine months is what’s most commonly prescribed. People with latent TB don’t need to go to the hospital. But, it’s essential that they take all of their pills. Or at least that they take the vast majority. This is the only way to ensure their body completely gets rid of the bacteria. Serious side effects from the antibiotics are uncommon. But it’s important for people to have regular monthly check-ins with their doctor just in case. Their doctor can work with them to modify their treatment plan if necessary.

It is possible to be re-infected after getting treated. But a person’s risk of contracting TB a second time is much, much lower.

Learn more about lung health and pulmonary medicine.