OLATHE, Kan. (WDAF) — A week after an Olathe elementary school was forced to close down due to absences and illness, the Johnson County Department of Health has identified the cause.

More than 150 students and staff were absent from Clearwater Creek Elementary on Oct. 26 and JCDHE says norovirus is to blame.

According to JCDHE and the Centers for Disease Control and Prevention, norovirus is a common illness that causes symptoms such as diarrhea, vomiting, nausea and stomach pain.

Clearwater Creek closed for the remainder of the week and implemented cleaning and disinfecting measures before reopening on Monday.

In a letter sent home to parents, the school said the health department recommends closure when absentee rates are above 10%. According to Clearwater Creek’s website, the school has a population of 540 students.