Officials in two states have confirmed they are working with federal officials on an investigation into Escherichia coli illnesses linked to lettuce served by a national restaurant chain.

Spokespeople with the Nevada and Vermont state health departments say the agencies are working with the federal agencies on the investigation. Both the U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) confirmed for Food Safety News on Friday that they have an open investigation into the outbreak, which had not previously been made public. A source close to the investigation says the implicated restaurant chain is Subway.

Health department officials in the other two outbreak states, Maine and New Hampshire, did not respond to requests for information about the outbreak and investigation. Vermont had five confirmed patients, Maine had four and New Hampshire and Nevada each had one.

A spokeswoman for the Vermont health department said the state’s five confirmed outbreak patients were all children. She could not provide any information regarding how many were hospitalized because of the department’s patient privacy policy. However, she said none of the children developed hemolytic uremic syndrome (HUS), which is a type of kidney failure that is often fatal. 

The Vermont spokeswoman echoed what federal officials said Friday in regard to why the public had not been informed about the outbreak when it was discovered. She said there wasn’t any actionable information for the public and that public risk has now passed.

However, as with the FDA’s statement, the Vermont spokeswoman said officials became aware of outbreak illnesses in November but then said that by the time the outbreak was discovered in December the illnesses had stopped.

The FDA and CDC are being notably silent on the outbreak and ongoing investigation.

“I am not sure we have more to add. I provided you the policy on actionable information,” an FDA spokesman said Monday.

The outbreak marks the second time in recent months when the FDA and CDC did not go public with information about an outbreak.

On Halloween, Food Safety News learned of an E. coli O157:H7 outbreak that the two federal agencies had not revealed to the public. It ended in September and involved romaine lettuce. 

Spokespeople from FDA and CDC said at the time that because they believed all of the implicated romaine had passed expiration dates by the time the outbreak was discovered, agency officials did not think the public needed to know.