A month after a science project made 28 students ill with salmonella at Jefferson Elementary School, several parents are accusing the school district of not being aggressive enough in dealing with the outbreak.

In a sternly worded letter dated July 10, more than 40 parents and residents — including some prominent town officials — charge that school officials ignored basic sanitary precautions, jeopardizing the health of students and parents.

Last week, the state Department of Public Health determined a fifth-grade science experiment involving the dissection of owl pellets in May was responsible for the outbreak, in which 28 students were confirmed to have the bacterial infections. In all, at least 50 students came down with related symptoms.

The letter alleges children were told they did not need to wash their hands or sanitize their desks after they conducted experiments; students were permitted to eat snacks at their desks after the experiments; and one student who brought in latex gloves for the experiment was told she could not wear them.