The flu bug hit two Des Moines schools and a Burien school hard in recent weeks.
On Jan. 26, 90 out of 384 Des Moines Elementary students were ill and missed school.
Three days later, 84 students were out sick at the 448-student Midway Elementary in Des Moines.
At Des Moines and Midway, most of the sick kids complained of gastrointestinal problems, according to Highline district spokeswoman Catherine Carbone Rogers.
Maintenance crews completed a major cleaning and disinfection of both schools including steam-cleaning carpets on the weekend.
Each evening since Jan. 26, janitors have been disinfecting doorknobs, desktops and other vulnerable locations.
Attendance was back to normal levels last week at the two schools, Rogers reported.
At St. Francis of Assisi School in Burien, 150 students out of a total enrollment of 465 missed school on Feb. 6.
The day before 150 students missed school at St. Francis, the private Catholic school received calls from 50 parents or guardians reporting their children would stay home because of illness.
Then, during the day, another 50 students left school with flu-like symptoms such as low-grade fevers, headaches and vomiting.
"I've been here for 15 years and I've never seen this before," observed Principal Sheila Keaton.
She reported the absence rate on the Friday before the Monday outbreak was normal.
"This spread like wildfire," Keaton added.
Absentees were down to about 90 by last Thursday, but Keaton urged parents to keep their children at home over the weekend so they could fully recover.
"We're hoping for a long, healthy weekend," She said.
Even after recovering from flu, a child's weakened immune system could make them prone to colds, according to Keaton.
Seattle-King County Health recommended that St. Francis not suspend classes because of the outbreak.