BUFORD, Ga. -- Elementary school students returned to their campus in Buford on Monday after the building was sanitized to prevent the spread of stomach flu.

Public health department officials recommended closing the Harmony Elementary School campus on Friday after more than 20 percent of the school's nearly 640 students as well as eight teachers showed symptoms of the virus.

Officials with the East Metro Health District visited Harmony Elementary Friday to investigate the cause of the students' illness as Gwinnett Schools crews cleaned the building. Health officials suspected the outbreak was caused by gastroenteritis, but wanted confirmation.

For about 24 hours, Madelynn Moreno was miserable.

When she went home from school last Wednesday, her stomach felt like it was turning inside out.

"My stomach started hurting and I threw up in the trash can," said the third grader at Harmony Elementary School in Buford, Ga.

The little girl’s misery didn’t end there.

“In the middle of the night, I threw up in the trash can again," she said.

Moreno was one of 131 children, nearly a quarter of the 639 students, who either stayed home sick or left school last Thursday.

They complained of diarrhea and vomiting. With all those kids sick, last Friday, officials decided to shut down the school for the day.

Karen Vickers’s first-grade daughter stayed home sick on Thursday, a day before the principal sent a letter telling parents telling them the school was closing because of the stomach-flu outbreak.

“I knew something was going on prior to getting a note sent home from my older child," Vickers said. “It was pretty icky for a while."

Gwinnett County School officials and the East Metro Health District, which oversees the county, disinfected the school last week to prevent the stomach flu from spreading.

The school reopened Monday morning.

Health officials have not concluded their investigation, but the number of children out sick dropped from 130 to 42 students.

Parents who dropped off their children said school officials did the right thing.

“I’m pleased they did what they had to do,” said Anjali Chandy.

Little Madelynn was feeling much better as her father, Joshua Baxter, walked her and her sister, Evangeline, to class.

"I felt confident everything got straightened out," Baxter said.

Madelynn added, "everything is going to be okay. If anybody does throw up, I'm going to be a little concerned."