BEIJING — On a subway car in Shanghai, commotion breaks out when someone spots a live chicken poking its head out of a bag tucked under one of the seats.
On a highway in Zhejiang province, a motorist is so panicked by bird droppings landing on her windshield that she stops the car and calls traffic police for help.
On the Internet, photos of dead sparrows on a Nanjing sidewalk are ordered removed by police who fear they might go viral.
The bird phobia gripping China is the result of a new strain of avian flu that has led to 17 deaths and 91 diagnosed illnesses over the last month.
Health authorities are concerned because of the unpredictable nature of the virus, known as H7N9. Unlike previous incarnations of avian flu, infected birds here show no signs of being sick, making it harder to stem the disease at its source.
So far, there is no evidence that the strain of flu can be easily transmitted from human to human; such transmission indicates a potential pandemic.
But the number of people having direct contact with birds is limited, so researchers are not quite sure how this year's patients have been getting sick.
Although the earliest cases involved farmers and poultry dealers, in more than half of the more recent infections the people had no direct contact with birds, Michael O'Leary, head of the World Health Organization's China office, said at a briefing Friday.
Consequently, the unknown has given way to fear. Pigeon fanciers around China have canceled events. Notices have gone up in diplomatic residences around Beijing instructing people not to take children to the zoo. Tables at Beijing's most popular Peking duck restaurant are now available without a reservation.
"People are scared. Nobody is buying chickens or ducks," said Li Guoli, a young man standing at a Beijing fresh market counter where the chicken legs weren't selling. At the next stall, business was so slow that the vendor was sound asleep.
Fifteen experts from the United Nations' top health agency are investigating the outbreak, concerned that it could become far more deadly.
"What we don't know is the size of the iceberg under this tip," O'Leary said.
The Chinese government appears to be struggling to contain the problem, without taking steps that would result in outright panic.
"It is a really challenging road to walk. You don't want to be hyperbolic and scare people, but you want to prepare for the worst-case scenario," said Myles Druckman, a vice president with International SOS, which advises companies on health issues.
As with other outbreaks in China, fear itself can prove economically devastating.
The 2003 outbreak of severe acute respiratory syndrome (SARS), which killed nearly 800 people, caused billions of dollars in financial losses.