A Modesto High School student has been diagnosed with active tuberculosis, school and county health officials said Wednesday.

Dr. John Walker, public health officer for Stanislaus County, said his agency was notified Tuesday after the boy was diagnosed through a medical screening.

The county Human Services Agency informed the high school at about 9 a.m. Wednesday, school officials said.

The school sent letters to parents Wednesday telling them there is no reason for students to stay home.

The boy is being quarantined at home. Once his medical treatment is complete and doctors determine he is not contagious, he will return to school, Walker said.

"This is a single case, and there is little probability the disease has been transmitted to others at the school site," Walker said.

Officials, citing confidentiality rules, did not release the student's name, grade or age. Principal Mary Byers said the boy has attended the school for two years.

Byers and a school nurse intend to talk with students and teachers today in each class the student attended to learn with whom he was in close contact. Classmates and staff will receive TB tests within two weeks. A follow-up screening will be done in June.

Anyone who tests positive will be referred to a county public health agency or a personal physician.

Walker said the agency is talking with the boy's family and friends to determine who might have been exposed.It's too early to tell how the teen-ager contracted tuberculosis, Walker said.

For centuries, tuberculosis ravaged populations before scientists discovered its cause in the 1880s and treatments brought the disease under control in the 20th century.

Today, health workers test for the disease by injecting a substance derived from the bacteria under the skin. If a lump forms, that indicates the bacteria has lodged in the person's lungs.

In most cases, a positive test indicates the person has latent tuberculosis, which means he or she has been exposed and the body has walled off the bacterium, Walker said.

Active TB can cause symptoms

The student has the active type, meaning the bacteria has escaped into the body and can cause symptoms of fever, coughing up mucus or blood, night sweats, shortness of breath and eventually death.

Walker said active TB is treated with drugs. He did not have an estimate on when the boy might return to school.

Officials are advising calm because the disease is difficult to transmit from one person to the next. It usually is transmitted through the air, by coughing or sneezing in close proximity to another's face.

"It requires prolonged contact, and we have so little tuberculosis in this county," Walker said.

The county had 22 cases of tuberculosis last year, and that is considered a low rate compared with other areas of the state.

Bee staff writer Ken Carlson can be reached at 578-2321 or kcarlson@modbee.com

Reprinted by permission of Modesto Bee.