Federal health officials commended Chipotle restaurants on Tuesday for closing outlets in Washington and Oregon, saying bold actions are what it takes to stop big, multi-state outbreaks of food poisoning.
But they still don't know just what type of food sickened at least 37 people who ate at the popular restaurant chain — or even if it is indeed a single outbreak.
"We don't yet know of a vehicle, what food caused it, or even with certainty that all of the cases that are identified there are related to each other," Centers for Disease Control and Prevention director Dr. Tom Frieden told reporters.
"We do know that Chipotle has closed many of its restaurants until more information is available," he added.
Chipotle said last week that it had closed 43 outlets in Washington and Oregon after 22 people became sick with a virulent type of E. coli infection. Washington and Oregon officials reported more cases Tuesday, bringing the tally to 37.
"I think it is always better to take a broad action than to narrow it down. They are being very responsible in their actions," Frieden said.
It's the latest multiple state outbreak of foodborne illness, the type featured in an unrelated report issued by CDC on Tuesday about the outbreaks.
"We don't have much more to tell you about this outbreak other than to tell you that it is the type of multistate outbreak that we are describing," Frieden told reporters.
Dr. Kathleen Gensheimer of the Food and Drug Administration says her agency spoke with Chipotle's senior management over the weekend.
"We have not yet identified any specific food. Nevertheless, Chipotle is sharing all their records with us, working with us in any way possible to get us information about their suppliers," Gensheimer said. She said Chipotle indicated an interest in coming to FDA after the outbreak has subsided to see what practices are contributing to outbreaks.
In its report, CDC said it found that outbreaks of foodborne illness mostly happen at the local level — say, an outbreak linked to a picnic or to a single restaurant. But the big, regional outbreaks are generally more serious.
"The leading causes of multistate outbreaks — Salmonella, E. coli, and Listeria — are more dangerous than the leading causes of single-state outbreaks," the CDC said in a statement.
"These three germs, which cause 91 percent of multistate outbreaks, can contaminate widely distributed foods, such as vegetables, beef, chicken and fresh fruits, and end up sickening people in many states."
Local outbreaks are more likely to be caused by norovirus, which is common and not usually deadly, CDC said.
"Multistate outbreaks have much more serious health effects than other foodborne outbreaks. The reason: the germs that cause most of the multistate outbreaks are deadlier," Frieden said. That's in part because these germs can persist and spread when food handling is consolidated in one place and then redistributed widely.
CDC analyzed 120 multi-state outbreaks that happened from 2010 to 2014. Only 3 percent of all reported outbreaks of foodborne illness crossed state lines, but they caused 7 percent of the illnesses — nearly 8,000 out of more than 71,000 reported illnesses.
And the bigger outbreaks send more people to the hospital: 34 percent of all 4,200 people hospitalized, and 56 percent of the 118 deaths.
Fruits, vegetables and beef were the biggest carriers of these germs, although Frieden noted that new techniques mean more unusual foods are turning up, such as the contaminated caramel apples that killed seven people last winter.
And most cases are never reported.
"For every case that is reported of Salmonella infection, there are 29 unreported cases," Frieden said. Only one in every 26 cases of E. coli is ever reported. Food poisoning looks like many other illnesses, including norovirus, and most victims recover without ever seeing a doctor.
One surprise: Imported food caused relatively few outbreaks or cases. "Imported foods accounted for 18 of the 120 reported outbreaks. Food imported from Mexico was the leading source in these outbreaks, followed by food imported from Turkey," the CDC said.
For instance, Mexico was the source of cucumbers implicated in a recent outbreak of Salmonella that killed four people and sickened 767 in 36 states.
Retail outlets such as restaurants can use tools such as data from loyalty cards to track down people who may have eaten contaminated food, Frieden said. And he encouraged retailers to buy from distributors who follow recommended safe handling practices.