"One girl came into the small animals department and was on the floor screaming," said Brittany Hersh, a Pleasanton resident who is working at the fair for the fourth year.
"I guess she got stung three times and she is allergic to wasps," said Hersh, a college senior who is also a summer intern in the Editorial Department of the Pleasanton Weekly.
Hersh and others alerted the paramedics, who treated the girl.
"Then we had to get everyone out of the rabbit barn early," she said.
The fireworks show started around 9:15 p.m., and about halfway through the show, at about 9:30, a group of yellow jackets was stirred up at the north end of the grandstands, fair spokeswoman April Mitchell said.
More than 70 people were stung despite the efforts of fair staff and law enforcement personnel to clear people from the grandstand area, Mitchell said. Everyone who was stung was treated at the scene by Alameda County firefighters.
The victims ranged from a 60-year-old adult to a 6-month-old infant, with some people suffering multiple stings, fire spokeswoman Aisha Knowles said. No one suffered serious reactions to the stings, and no one needed to be taken to a hospital.
Investigators initially thought the stings were from bees, but 10 insect carcasses were collected and determined to be ground-burrowing yellow jackets. The area was inspected and a ground nest was discovered. The nest was later cleared from the area.
Investigators believe the launching of the fireworks may have vibrated through the ground and disturbed the nest, Knowles said.
Mitchell said this was the first incident of this proportion involving insects on the fairgrounds.
However, it was the second incident in as many days that caused injuries at the fair. On Thursday, a roller coaster ride malfunctioned, causing minor injuries to five children and two adults. At about 3 p.m. Thursday, a connector link on a chain at the "Wacky Worm" ride appears to have pulled apart, causing the chain to dangle in front of the ride and hit the passengers, Mitchell said.
The ride was shut down for inspection after the incident, and the California Division of Occupational Safety and Health cleared the ride for repair Thursday evening. The ride reopened Friday afternoon after being repaired.