Three of 19 children with laboratory-confirmed Salmonella infections are being treated in Ottawa hospitals in an outbreak that has also sickened four adults.

Health officials in Canada’s capital city investigating the outbreak have focused on a catering company called The Lunch Lady, which serves meals to 55 schools and day care facilities.

Among the 16 lab-confirmed cases are children ranging in age from 15 months to 14 years old who attended three different schools and one daycare, according to CBC News. Most of those sickened became ill between March 1 and 8.

The Lunch Lady has three kitchens in Ottawa. An owner of two Lunch Lady franchises, Jonathan Morris, said public health investigators are focusing on the Boyd Avenue kitchen. The kitchen is closed this week for spring break, and Morris said he learned of the Salmonella outbreak while on vacation in Florida.

In an email sent to parents, Morris said tacos and meat lasagna have been implicated as possible sources of the outbreak, according to a report in the Ottawa Citizen. Morris says the company is cooperating with the investigation.

Dr. Isra Levy, Ottawa’s top public-health official, told the paper that several of the children infected with Salmonella ate one or both of those dishes, but the investigation at this point is very preliminary, so there is no known source.

The catering company has passed regular investigations by Canada’s health authorities, and Levy said the outbreak could have been caused by anything from a bad batch of beef to a kitchen worker who didn’t wash his hands after handling a pet turtle.

On average, Ottawa sees about 160 Salmonella infection cases during the year. They are typically sporadic, meaning health officials found no connection among them, and often they involve returning travelers.

In this outbreak, Levy has sent an alert to the city’s physicians, asking them to be on the look out for others who may be ill.

Salmonella brings on nausea, vomiting, dehydration and bloody stools. The symptoms can appear in six to 72 hours after consumption of contaminated food or water. Children and the elderly are more likely to be affected.