A pet turtle in a fifth-grade classroom may have caused the salmonella outbreak at Jefferson Elementary School, according to state health officials.

The number of sick children jumped to 11 yesterday, after doctors reported their young patients had the bacterial infections, said Department of Public Health spokeswoman Donna Rheaume. School officials Monday could only confirm six cases, including a first-grader. Another 40 or 50 children, most of them also fifth-grade students, have reportedly suffered gastrointestinal illnesses, including vomiting, diarrhea and stomach cramps.

The DPH is now looking at the water in the turtle’s aquarium as a possible contaminator, while still exploring a link to a fifth-grade science experiment involving the dissection of owl feces.

School Committee Chairman Jeffery Roy said the school has cooperated with the investigation and hopes to soon learn the source. The building was sanitized this week on the advice of experts, and Roy said he would consider making policy or curriculum changes if they are recommended.