Health experts have issued a warning about a significant outbreak of the worst disease in the world at a California high school.
Due to resistance to some antibiotics and increased spread in developing nations without access to modern medications, nearly one in five students and staff at San Francisco’s Archbishop Riordan High School have tested positive for tuberculosis (TB), a respiratory disease that is thought to be the deadliest disease on the planet.
According to the San Francisco Department of Public Health, there have been seven active cases since the outbreak started in November.
There were also 241 latent cases, which are people who have Mycobacterium tuberculosis, the germ that causes tuberculosis, in their bodies but whose immune systems are preventing an active infection.
In a letter to the school community on April 27, health officials stated, “People with latent TB infection (LTBI) are not contagious, but if left untreated, latent TB could develop into active TB – a serious illness.”
In order to safeguard their long-term health as well as the health of others around them, it is crucial that individuals with latent TB receive treatment.
About 1,200 pupils attend the institution, which costs roughly $30,000 a year.
According to the letter, an infectious person was last found on school property on February 19, and four active and three suspected cases of tuberculosis were recorded in February.
Health officials said that nearly one in five students and workers at San Francisco’s Archbishop Riordan High School (seen above) tested positive for TB.
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According to health officials, people who were exposed to a recently confirmed TB case or who belong to “a small group of individuals with new LTBI cases identified on this round of testing” will be the focus of testing starting on Wednesday and Friday of this week.
In March, the entire school community underwent testing, which, according to a statement from health officials to SFGate, “indicate a strong reduction in transmission.”
The expanded testing is “out of an abundance of caution,” according to the department.
A TB cluster is defined by the California Department of Public Health as having four or more active cases.
Dr. Monica Gandhi, an expert in infectious diseases at the University of California, San Francisco, told SFGATE, “This is a big outbreak.”
She added that although latent tuberculosis does not exhibit symptoms, the high proportion of students who have been diagnosed with the illness is uncommon.
“That kind of latent TB does not exist in children in this country,” she stated. “Those kinds of numbers, of 20 percent having latent TB, are in low-income countries.”
Every year, TB kills about 500 Americans after infecting a few thousand, but the hazard is far more common in developing nations. Every year, 1.2 million individuals die from tuberculosis worldwide.
The Bacillus Calmette-Guérin (BCG) vaccine is the primary means of preventing tuberculosis (TB) worldwide; however, due to the low risk of TB in the United States, BCG is not routinely provided, with the exception of children who are frequently exposed to individuals who have active TB or healthcare personnel who work in high-risk locations.
The microorganisms that cause tuberculosis, Mycobacterium tuberculosis, are shown here (stock image).
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The Mycobacterium tuberculosis bacteria, which causes tuberculosis, is discharged into the air when a person with active tuberculosis coughs, sneezes, or speaks. A chronic cough, occasionally coughing up blood, chest pain, unexplained weight loss, fever, night sweats, and appetite loss are among the early signs.
Later on, the infection may spread to other organs, including as the brain and spine, and patients may suffer from severe breathing problems and substantial lung damage.
TB in the brain, often called tuberculous meningitis, can cause strokes or paralysis by killing nerve cells, damaging important structures, and raising intracranial pressure. The most common cause of death is respiratory failure brought on by bacterial lung disease.
From 1993 until 2020, the total number of TB cases in the US fell steadily to an all-time low of 7,170. However, that figure increased to 7,866 in 2021.
Since then, the prevalence has increased annually.
According to the most recent CDC data, the US tentatively reported 10,110 TB cases in 2025, a tiny decrease from 10,330 in 2024—the highest number since 2011, when there were 10,471 cases. Non-US citizens accounted for the majority of 2025 cases (7,858).
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Eighty percent of US states saw an increase in instances in 2024, which experts attribute to missing cases and mistrust of physicians created by the Covid epidemic. Cases in California reached a 12-year high of 2,150 in 2025.
Additionally, state health officials reported a “substantially higher” illness rate in 2025 (5.4 infections per 100,000 versus 3 per 100,000 nationwide).
Beginning in 2001, the demographics of tuberculosis have also changed. For the first time, the CDC reported more patients who were not citizens of the United States than those who were, indicating that travellers and immigrants were the primary source of infections.
Antitubercular medicines, such as isoniazid (INH), rifampin (RIF), pyrazinamide (PZA), and ethambutol (EMB), can be used to treat active TB. To make sure the bacteria has been completely eradicated, they are often taken for at least six months.
