It may take months to find out when, where and how a Merced High School student contracted tuberculosis, experts said.
And it also may take months to find out if any one of up to 200 people who had "prolonged" exposure to the student may have contracted the infection.
The Merced County Department of Public Health notified Merced High officials on March 12 that a student was diagnosed with TB, school officials said.
The health department sent official notices to the school on March 13, and the school reportedly notified parents in multiple languages on March 15.
The health department on Wednesday started screening students, parents and anyone who has had "prolonged" contact with the student since November, said Richard Rios, public health program manager for the health department.
"We're looking at symptoms ... potentially in the early months in 2018," Rios said, noting that there is generally a three-month "incubation" period in which a person can carry the bacteria that attacks the lungs and causes TB.
"An infection doesn't occur overnight," Rios said. "It could take weeks."
The results of Wednesday's screenings can rule out anyone who doesn't have the infection, Rios said. But anyone testing positive doesn't necessarily have the infection.
Some people can have the latent TB-causing bacteria but not exhibit signs of an infection, Rios said. Some could even have it for years before it starts to infect a host.
And because the infection doesn't become airborne contagious until symptoms start showing, those testing positive with the skin test will need to undergo further examination. The process could take several months.
"This is routine," Rios said, noting that the risk for students and others to contract the disease is low. "This one, the public hears about because it involves a high profile location. This is being done all the time."
Following news of the TB diagnosis, Merced High communicated as much as it could about the infection and any risks to students, said Ralph Calderon, a deputy superintendent for the Merced Union High School District. There was no related drop in attendance,
"We're following guidelines from the health department," Calderon said, adding that the district is putting updates and information on the school's website.
The Merced high school student marks the first reported case of TB in Merced County in 2018, Rios said. Merced County averages about 10 cases per year.
It isn't the first time a Merced County high school dealt with a TB infection. In 2005, a student at Atwater High School reportedly was infected with TB, Rios said.
The health department is urging people to educate themselves on TB. The symptoms include coughing lasting three or more weeks, coughing up blood, chest pain, pain with breathing or coughing, unintentional weight loss, fatigue, fever, night sweats, chills and loss of appetite, according to the Mayo Clinic.
If anyone shows these symptoms, they are advised to first get a checkup with their primary care physician. Those unable to reach a physician are encouraged to call the health department at 209-381-1023.