A Japanese health official admitted that a doctor diagnosed with tuberculosis examined over 600 patients without wearing a protective mask.
The doctor, who is in his 50s and runs a clinic in central Ito city, began displaying symptoms of the potentially lethal airborne disease in mid-August, but brushed them off as a common cold, the health authority official said.
He continued to see patients, without wearing a face mask, until he was diagnosed with tuberculosis earlier this month.
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.
The disease is found all over the planet, but is more common in the developing world, where it also has a much higher mortality rate.
Letters were being sent to all patients examined by the doctor, the health authority spokesman said, adding that the names of the clinic and the doctor were not being disclosed.
"It is only 10 to 15 percent of people who suffer actual symptoms after they are infected with tuberculosis," he said.
"It also takes two to three months before they start showing these symptoms," he said, when pressed over why the authority had not acted more quickly in alerting people to their possible infection.
The doctor has since been hospitalised for treatment.
Globally, 87 percent of those diagnosed with TB were successfully treated in 2010, the last year for which data is available on the WHO website.