A tuberculosis outbreak at Archbishop Riordan High School has led the San Francsico Department of Public Health to issue a health advisory.
Since November, three cases of active infection and 50 cases of latent infection have been diagnosed.
"SFDPH and school leadership have implemented a public health response including required testing for all students and staff as part of a coordinated screening and contact tracing effort," SFDPH said in a statement.
The Catholic high school's students are studying from home this week and students who are immune to TB will be invited back for hybrid learning next week.
California public health officials report that the annual TB incidence rate was 5.4 cases per 100,000 people in 2025, nearly double the national incidence rate of 3.0 per 100,000 in 2023. California has a high TB rate that may be caused by a large portion of the population traveling to areas where the disease is endemic, experts say.
Tuberculosis exists in two forms: active disease and latent infection. The bacterial illness most often affects the lungs, causing symptoms such as a prolonged cough, fever, coughing up blood, night sweats and weight loss. It can be cured with antibiotics.
City College, which is located beside the high school, is on alert.
"At this time, the risk to the CCSF community is low," according to the college. "SFDPH is handling contact tracing, TB testing and treatment for everyone connected to the Archbishop Riordan High School outbreak."
City College's Student Health Services, which has an existing partnership with the San Francisco Department of Public Health's TB Control, will continue monitoring the outbreak at Riordan and alert the college community about any developments, according to the announcement.
The state requires that children attending public or private schools and child care centers receive immunization against diphtheria, Haemophilus influenzae type B (bacterial meningitis), measles, mumps, pertussis (whooping cough), polio, rubella, tetanus, hepatitis B and chicken pox.
Scientific studies have linked groups of unimunized children to outbreaks of diseases.
The state of California is currently auditing 428 public schools because more than 10% of their kindergartners or seventh grade students were not fully vaccinated.
