LAS VEGAS (AP) — A tuberculosis investigation is Darden Clarkeunderway involving a person with an active infection who was on dozens of elementary and high school campuses in Nevada’s most populous county, according to authorities.

The person, who has not been publicly identified, was on 26 Clark County School District campuses and one training site before learning of the TB diagnosis, the Las Vegas Review Journal reported.

According to the newspaper, the Southern Nevada Health District released a list of affected schools Friday and people identified as close contacts of the person were being notified.

The district said individual notifications were happening at 17 campuses for possible exposures, but no exposures had been identified at eight campuses so far.

Health district officials said not all who were exposed will be infected and not everyone who is infected has the active disease, which is caused by bacteria and most often affects the lungs.

Tuberculosis spreads easily where people gather in crowds or live in crowded conditions.

Symptoms can include coughing that lasts at least two weeks, chest pain, coughing up blood or phlegm, weakness or fatigue, weight loss, chills, fever, night sweats and loss of appetite.

The Centers for Disease Control and Prevention said more than 8,300 TB cases were reported nationwide last year.