An outbreak of tuberculosis (TB) has been linked to a San Francisco high school.

The San Francisco Department of Public Health (SFDPH) issued a health advisory on Jan. 29 about the outbreak, which has been tied to Archbishop Riordan High School.

TB is a curable bacterial infection that targets the lungs, but can also infect other organs, according to Johns Hopkins. It is an airborne contagion that can be spread through coughing, sneezing or saliva.

Three active TB cases have been diagnosed among people associated with Archbishop Riordan High School since November 2025, according to the advisory, and over 50 latent TB infections have been identified within the school community.

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A person with a latent infection has been infected with the tuberculosis bacteria, but the bacteria are inactive in the body.

While latent-stage TB is not contagious, it can develop into active disease in 5% to 10% of people.

“Efforts are underway to assure preventive treatment for all these individuals,” the advisory states. 

The school’s staff and students have been instructed to stay home if they are sick and to get medical clearance from a doctor before returning.

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“Additionally, TB evaluation is required for all students and staff affiliated with the school, regardless of symptoms,” the advisory stated. “Repeat TB assessment will be required every eight weeks until the outbreak is resolved.”

“At this time, risk to the general population is low, so these measures are not needed for patients who are not connected to the AHRS outbreak.”

“If you breathe, you can catch TB — so all people are at risk.”

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In the U.S., more than 565 people died from TB in the most recent complete year of official data available, according to the Centers for Disease Control and Prevention.

There is a greater than 10% case fatality rate in San Francisco, per health officials.

Symptoms, diagnosis and treatment

While around 25% of people have likely been infected with the TB bacteria, just 5% to 10% will experience symptoms and develop the disease. Only people with symptoms are contagious.

Those who get sick with TB may experience mild symptoms, including coughing, chest pain, fatigue, weight loss, weakness, fever and night sweats, according to the CDC.

In addition to the lungs, the disease can also affect the kidneys, spine, skin and brain.

“TB can affect any organ of the body, but it causes disease in the lung in over 80% of cases,” Masae Kawamura, M.D., a former TB control director in San Francisco and a tuberculosis clinician, previously told Fox News Digital. “This is dangerous because it causes cough, the mechanism of airborne spread.”

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In more severe cases, patients may cough up blood, noted Kawamura, who serves on the board of directors of Vital Strategies, a global public health organization. 

“Often, there are minimal symptoms for a long time and people mistake their occasional cough with allergies, smoking or a cold they can’t shake off,” she added.

TB can be identified with rapid diagnostic tests. The disease is treated with antibiotics that are taken every day for four to six months, the CDC states. Some of the most common include isoniazid, rifampicin, pyrazinamide and ethambutol.

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Failing to take the complete course of medications can cause the bacteria to become drug-resistant, which would then require treatment with different medications.

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If TB goes untreated, it is fatal in about half of its victims, according to Kawamura. “About 25% recover on their own and another 25% persist as chronic active TB cases,” she said.  

Who is at risk?

“If you breathe, you can catch TB — so all people are at risk,” said Kawamura, who calls TB a “social disease of crowding and mobility.” 

“Since TB is airborne, congregate settings like hospitals, nursing homes, prisons, jails, classrooms and homeless shelters are places TB is more easily spread, especially if multiple risks are involved,” she added.

Those at the highest risk of developing TB disease after exposure include people who have diabetes, have weakened immunity, are malnourished, use tobacco and/or drink excess amounts of alcohol. Babies and children are also at higher risk.

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The best means of prevention is testing those at risk and treating latent tuberculosis infection, according to the doctor.

Fox News Digital reached out to Archbishop Riordan High School requesting comment.

The U.S. is in the thick of flu season, with many states reporting “moderate to very high activity” of influenza-like illness, according to the CDC.

With influenza A (H3N2), or subclade K, making up a large portion of the circulating viruses, doctors emphasize the importance of getting the most recent flu vaccinations, staying at home while sick and washing hands frequently, among other prevention tactics.

If you’ve been exposed to or infected with influenza, here’s what to know about how long the virus is transmissible.

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“You are typically contagious with the flu for five to seven days after symptoms start,” Dr. Samantha Picking, the Massachusetts-based senior director of immunizations at Walgreens, told Fox News Digital.

“However, some groups remain contagious for longer periods. Young children and people with weakened immune systems can spread the virus for more than seven days, sometimes extending to two weeks or longer.”

It’s a myth that people can’t be contagious until they experience symptoms, according to Picking.

“The flu is most contagious during the first three to four days after symptoms appear,” she said. “However, you can begin spreading the virus a day before feeling ill and may remain contagious for up to a week or longer.”

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The incubation period — the time between exposure to the virus and when symptoms start — is typically two days, though it can range from one to four days, the pharmacist added. People with mild symptoms can still spread the flu. 

For anyone who is starting to feel sick or has been around someone who has the flu, Picking recommends limiting contact with others to avoid spreading the virus.

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“To be safe and prevent spreading the virus, stay home until you’re fever-free for at least 24 hours without using fever-reducing medicine,” Picking advised. “For most healthy adults, this typically corresponds to five to seven days after symptoms begin.”

People can take extra precautions, like masking, for a few days after returning to normal activities, she added.

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“However, use your best judgment and consult a healthcare professional if you’re unsure whether you’re well enough to leave the house,” she added. “If your other symptoms aren’t improving, or you generally still feel ill, it’s wise to stay home and practice good hand hygiene.”

Young children and people with weakened immune systems may be able to spread the virus to others for a longer time period, sometimes for up to 14 days, according to the pharmacist.

“Stay home until you’re fever-free for at least 24 hours without using fever-reducing medicine.”

Picking noted that a cough can linger for weeks after other symptoms have abated. “While a lingering cough is not necessarily a sign that you’re still contagious, it’s considerate to mask up and practice good cough etiquette when around others,” she advised.

Some antiviral medications, when initiated early on, can shorten how long someone is contagious with the flu.

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“These medications work best when started within two days of seeing symptoms,” Picking noted. Anyone who is interested in antivirals should speak with a healthcare provider or pharmacist for personalized guidance. 

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Flu symptoms can include fever, chills, headache, fatigue, cough, sore throat and runny nose.

Subclade K has been detected as the culprit in rising global cases, causing more intense symptoms and higher risk of spread.

“It’s becoming evident that this is a pretty severe variant of the flu,” Dr. Neil Maniar, professor of public health practice at Boston’s Northeastern University, previously told Fox News Digital. “Certainly, in other parts of the world where this variant has been prevalent, it’s caused some severe illness, and we’re seeing an aggressive flu season already.”

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“The vaccine still provides protection against serious illness resulting from the subclade K variant that seems to be going around,” he added.

Angelica Stabile contributed reporting.

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