A bacteria spread through contact with contaminated water is to blame for an illness that sickened 92 people at a July 4 event, state health officials said Tuesday.

Lab tests determined the culprit to be the shigella bacteria, which can cause gastrointestinal distress. Sixteen of those sickened at Spring Lake Beach in Burrillville were hospitalized and four remained in the hospital on Tuesday, but none of the illnesses was believed to be severe.

State Health Director Michael Fine said anyone who swam in the lake Thursday should seek medical attention if they develop gastrointestinal symptoms but that the illness often resolves on its own.

“We expect to see new cases over the next week — but not lots of new cases,” he said. “We know that no one is severely ill.”

The beach is expected to be reopened Wednesday. Tests of the water show no continuing shigella contamination.

Officials believe the illness was spread through contact with water contaminated with human feces. Most of those sickened are under 18, and Fine said the young are especially vulnerable. An estimated 2,000 people were in the lake on July 4.