The Thai taxi driver got stuck in traffic because that’s what often happens in Bangkok. To pass the time, the woman took out her phone and, leaning forward, pointed out some tourist sites she might want to visit.

Then she sneezed, the spray showering the cabby’s face.

“I thought, she’s pretty but she doesn’t have any manners,” said Thongsuk Thongrat, the taxi driver.

About a week later, Mr. Thongsuk, 50, tested positive for the coronavirus that has been spreading across the globe from China and has infected at least 41 people in Thailand.