Cases of tuberculosis (TB) — an illness that kills more people than any other infectious disease — rose in the U.S. during 2022, per the Centers for Disease Control and Prevention (CDC). And some doctors are concerned that limitations of testing at the border could be partly to blame for the surge.

In 2021, the disease infected nearly 11 million people and caused 1.6 million deaths worldwide, according to the World Health Organization (WHO).

Tuberculosis is a highly contagious disease caused by a bacterial infection. It primarily affects the lungs, but can also affect the brain, kidneys and spine. 

The CDC states that all refugees ages two and older must be tested for tuberculosis before entering the U.S.

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"By law, refugees diagnosed with an inadmissible condition are not permitted to depart for the United States until the condition has been treated," the agency states on its website. 

The CDC uses its Electronic Disease Notification (EDN) system to notify federal, state and local health departments of any immigrants and refugees who are found to have medical conditions that require follow-up.

There are limitations to that process, however.

"By design, the EDN system only collects information for the approximately 10% of immigrants who have an overseas medical classification," explained Neha Sood, health communication specialist for the CDC in Atlanta, Georgia, in a statement to Dr. Marc Siegel, clinical professor of medicine at NYU Langone Medical Center and a Fox News medical contributor. 

"Thus, DHS [Department of Homeland Security] data were used to approximate the immigrant denominators."

There is also some degree of human error that comes into play, Sood added.

"Because data transfer for immigrants during the study period primarily relied on staff at ports of entry to correctly review, retain and route paper forms for each immigrant with a medical classification, human error likely caused some losses, resulting in possible underestimates of immigrants with medical classifications," she said.

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While health departments are "encouraged and provided incentives" to share the results of immigrants’ testing with the CDC, Sood said there is always the chance of "underreporting."

She added, "The proportion of immigrants, refugees and eligible others who completed a post-arrival examination might be higher than indicated in this report."

Although the CDC has "comprehensive surveillance systems" to track communicable diseases within the U.S., the agency does not track diseases by immigration status, Sood explained.

Linda Yancey, M.D., a specialist in infectious disease who is affiliated with Memorial Hermann Health System in Houston, Texas, said she regularly sees people who have screened positive for the disease and need treatment to prevent developing symptomatic illness.

"Tuberculosis is quite common in Texas, especially in the big cities," she told Fox News Digital. "Houston is an international port of entry, so we get people from TB-endemic areas coming here frequently."

Most of the imported tuberculosis cases seen at Memorial Hermann are among people coming from Africa and the Indian subcontinent, Yancey said. 

"This is why immigrants coming into the U.S. are screened at the time of entry," she said.

"People can be exposed to TB years before they become contagious," she went on. "By doing early screening, we are able to treat people long before they develop severe pneumonia."

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Immigrants who have positive screenings are given three to four months of pills to protect their TB from developing into an illness, Yancey said.

In a 2022 study by the University of Texas, researchers analyzed patterns in tuberculosis patients who had been diagnosed when crossing into the U.S. from the Mexican state of Tamaulipas, which serves as a "migration waypoint."

The study, which was published in the Journal of Immigrant and Minority Health, found that an average of 30% of immigrants screened positive for tuberculosis over an eight-year period.

Immigrants with tuberculosis may be less likely to get successful treatment due to various factors, the study authors also wrote in a discussion of their findings.

The barriers to treatment that were cited included mobile living conditions, economic constraints, fear of deportation and the policy of the host country to provide free TB therapies.

Another concern is the type of TB that potentially could be coming into the U.S.

James Hodges, M.D., an internist in Waco, Texas, is concerned that immigrants are bringing in a drug-resistant strain of the disease.

"I have found that immigrants who are positive for TB are more likely to have a drug-resistant type," he told Siegel.

"This is likely due to the over-the-counter meds and antibiotics that are available in Mexico and other central and South American countries — these patients have incompletely treated coughs on their own," Hodges continued. 

"This is becoming more common with the last two years of an open border."

Tuberculosis treatments need to be "specialized, complex regimens," Dr. Siegel explained. "Here in the U.S., we use INH, Rifampin, PZA, Ethambutol and others. If you use an over-the-counter antibiotic that only partially treats TB, resistance is more likely to emerge."

Exposure to tuberculosis is very common, but only about 20% to 30% of people who are exposed to it become infected, according to Mount Sinai.

Most new infections occur when bacteria enter the air after the infected person coughs or sneezes, and is then breathed in by someone else.

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A majority of people who get the infection will have no symptoms and are not contagious, which is known as "latent tuberculosis."

Those who have "active infections" develop the disease, experience symptoms and can potentially spread it to others.

During the first stage of TB, most people don’t experience any symptoms, though some may have a mild fever, cough and/or fatigue.

Patients who develop an active infection — either immediately after the primary infection or after months or years of a latent infection — may experience coughing (sometimes with blood or mucus), chest pain, pain when breathing or coughing, fever, chills, weight loss, night sweats, loss of appetite and/or fatigue, according to the Mayo Clinic’s website.

Some people may develop extrapulmonary tuberculosis, which is when the infection spreads from the lungs to affect other parts of the body. 

There is currently no vaccine for TB available in the U.S. 

Diagnosis can be made via a skin test or a blood test.

For those who have positive screenings, additional tests — including chest X-rays, CT scans and lab analysis of lung fluid — can determine the extent of the infection and the impact on the lungs, according to the Cleveland Clinic website.

There are multiple treatments available for both latent and active tuberculosis, Yancey said.

"For latent disease, we treat with drugs like rifampin, rifapentine and isoniazid," she said. "People only need to take the pills for three to four months."

For active disease, additional pill options include pyrazinamide, ethambutol, moxifloxicin and linezolid, Yancey said. 

There is also an injectable option called amikacin.

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"Because we have so many different options to treat TB, drug shortages are very seldom an issue," Yancey said. "If one drug is in short supply, we have multiple effective alternative regimens."

Medications are typically taken for a period of at least six to nine months. 

If left untreated, the disease can be fatal.

"If you have tuberculosis and you’re treated, your outlook is good if you’ve followed directions and taken your medications for as long as you should and in the way you were told," the Cleveland Clinic’s website indicates.

People who experience chest pain, severe headache, seizures, confusion, difficulty breathing, bloody mucus or blood in the urine or stool should seek emergency medical care right away, per the Mayo Clinic.