Health officials have new questions about a deadly salmonella outbreak that has sickened nearly 900 people nationwide, the Centers for Disease Control and Prevention (CDC) said this week.

Since the beginning of July, the CDC says 888 people in 39 states have been affected by the outbreak, which has been blamed on contaminated cucumbers that were imported from Mexico.

The outbreak has killed at least four people and sent 191 people to the hospital, the CDC said.

After an investigation, Andrew & Williamson Fresh Produce and Custom Produce Sales each initiated cucumber recalls in the first half of September as a result of possible contamination.

However, the CDC’s latest update on the outbreak said 106 people have fallen ill after Sept. 24, when all of the recalled cucumbers should have been either off the shelves or spoiled. That includes 50 people who have gotten sick since Nov. 19, when the CDC last issued an update.

The CDC said an investigation into the new illnesses is ongoing, and officials are trying to determine if cross-contamination from the recalled cucumbers could be to blame.

The organization is encouraging anyone who might have bought or sold recalled cucumbers to wash and sanitize drawers, shelves, crates or reusable grocery bags where the vegetables were stored.

The CDC has not yet determined any other food item that could be causing people to get sick.

Illnesses have been reported in every state except Maine, Massachusetts, Rhode Island, Vermont, New Jersey, Delaware, Michigan, West Virginia, North Carolina, Georgia and Mississippi.

While the rate of reported illnesses has dropped since the recalls were issued, the CDC says it’s still above what is expected for this time of year. And the latest update indicated one person got sick in Tennessee, a state that had not previously reported any illnesses tied to the outbreak.

Salmonella usually triggers a mild illness that can cause fever, diarrhea and abdominal cramps, the CDC says, and most people recover within a week without any treatment. But children, older adults and those with weak immune symptoms are particularly at risk of severe infections.

According to the CDC, an estimated 1.2 million people in the United States get sick from salmonella every year. About 19,000 of them are hospitalized and about 450 of them die.

California has reported the most illnesses tied to this outbreak, with 241 people getting sick there. The CDC said that three of them died, though salmonella likely wasn’t a factor in two cases. The outbreak is also being blamed for one death apiece in Arizona, Oklahoma and Texas.