A massive tuberculosis outbreak at a high school in Gyeonggi Province carries little risk of contagion, health officials said Friday.

According to the Korea Center for Disease Control and Prevention, 128 of Goyang Foreign Language High School’s 471 second-graders were found to have been infected with latent TB. They are in the pre-symptomatic and pre-disease stage of the disease and thus are not infectious, the agency said.

A person with inactive TB is not ill, but may develop symptoms later when his or her immune system becomes weak, it explained.

Only four cases have been confirmed in the school since January ― two in second grade and another two in third. The three of them had active TB and have been treated, while the fourth is receiving treatment at a hospital.

“All second graders have been tested. Screening tests are now being carried out on first and third graders,” said an official at the KCDC.

Some 104 students in the third grade positively reacted to the initial screening test and are being further assessed, the official said.

Tuberculosis usually attacks the lungs, but can affect almost any part of the body. It is spread through the air when people who have an active TB infection cough, sneeze or otherwise transmit their saliva through the air.

By Lee Sun-young (milaya@heraldcorp.com)