A doctor who didn’t know he has the potentially lethal airborne disease tuberculosis had contact with 658 people, including family members, clinic staff and more than 600 patients, five of whom were children, according to Japanese health officials.

The 50-something doctor runs a medical clinic in Ito, Shizuoka Prefecture, a resort area 120 kilometers southwest of Tokyo.  He began displaying symptoms of TB in mid-August, but brushed them off as a common cold.  Officials say the doctor continued to see patients, without wearing a facemask, until he was diagnosed with tuberculosis earlier this month.

The good doctor has since been hospitalized for treatment, and officials are investigating his past contacts to learn if he spread the disease.

Tuberculosis is a bacterial infection that attacks the lungs and can be transmitted by coughing or sneezing. It kills approximately a million people around the world every year, according to the World Health Organization.