A physician and two others were diagnosed with coronavirus in Kishoreganj on Tuesday.
Civil Surgeon Dr Md Mujibur Rahman confirmed the development in the evening.
"So far, 18 people in the district have tested positive for coronavirus," he said.
Meanwhile, the local administration locked down Karimganj Upazila Health Complex after a doctor and a staffer were diagnosed with coronavirus, Rahman said.
Another patient is from Bhairab upazila, the civil surgeon said.
Earlier on Monday, two doctors of the health complex also tested positive for coronavirus in the upazila, said Upazila Nirbahi Officer Taslima Nur Hossain.
Meanwhile, seven more people died from coronavirus in Bangladesh in the last 24 hours till Tuesday, taking the death toll in the country to 46.