Students in nine schools reported illness shortly after eating school lunches. The illnesses were brief in duration. Predominant symptoms included: headache; nausea; abdominal cramps; dizziness. The outbreaks occurred over a 16 month period beginning in February, 2003. An investigation by the Massachusetts Department of Public Health found significant risk associated with eating flour tortillas. This led to a traceback investigation to the Del Rey Tortilleria based near Chicago, Illinois. An investigation into the conditions in the plant and unopened tortilla packages found improper labeling and high levels of food-processing chemicals, respectively. In particular, investigators found ten times the normal level of calcium propionate and fifty times the normal level of potassium bromate.