A suspected norovirus outbreak sickened dozens of students at a Lafayette elementary school last week.
On Friday, more than 100 students were absent from Burton Valley Elementary School -- more than four times the normal absence rate, Lafayette School District Superintendent Fred Brill said.
Many of those students exhibited typical norovirus symptoms, such as nausea, vomiting and diarrhea, according to Contra Costa Public Health Nurse Susan Farley, who has been working with the school district since the outbreak.
Also on Friday, a higher-than-average number of students were absent at Stanley Middle School -- possibly including siblings of sickened Burton students, according to Brill.
The superintendent said school principals last week informed parents of the outbreak and asked that any children suffering from the virus be kept home from school for an additional 48 hours as a precaution.
Since Friday, custodians have been scrubbing down and sanitizing surfaces at both campuses.
"Hopefully it will not spread to other schools, but we are tracking it," Brill said.
By Wednesday, many of the students who missed school on Friday had returned, with just 51 absences reported at Burton Valley.
According to Farley, the outbreak could be one of about a dozen norovirus outbreaks across Contra Costa County in recent weeks.
The highly contagious virus circulates throughout the year but tends to reach its peak in winter, she said.
"It's been called the 'winter vomiting disease,'" Farley said.
The nurse said the best way to prevent the spread of norovirus is for infected people to stay home. People are also advised to thoroughly wash their hands with soap and water rather than reaching for alcohol-based anti-bacterial gels, which are not effective against the virus.