Fifty percent of students from Woodville School in Wakefield, MA, were absent from school Thursday.
A group of students who had returned from a trip to Spain may have contracted norovirus from a contaminated water source.
More than 200 students and one dozen staff members were absent last Thursday, and it was reported that even more students went home sick.
The study found norovirus infections result in more than 200,000 fatalities per year and cost health care systems more than US$4 billion.
Testing has linked the outbreak to bottled spring water that had been contaminated with human fecal material.
The cost to control the outbreak could reach six figures by Monday.
Daily restroom upkeep