An outbreak of E. coli bacteria at a Portola Valley retirement community has stricken as many as 24 residents and employees, sending seven seniors to the hospital, one in critical condition.
Public health officials spent Thursday reassuring residents and trying to track down the source of the intestinal infection at The Sequoias, a 315- resident complex that includes apartments, an assisted-living wing and a skilled nursing facility.
A possible clue is that four of the sick people were food service employees, said San Mateo County Deputy Public Health Officer Sam Stebbins. E. coli bacteria is often found in undercooked meat, contaminated vegetables or unpasteurized milk or juice.
Food contamination "is the most likely possibility at the moment,'' Stebbins said. "But we don't have any suggestions as to which type of food." Food service workers provide meals throughout the facility and the illness has struck residents at all three of the complex's living settings.
Stebbins conducted a meeting with residents of the facility Thursday, broadcast via closed-circuit television. Meanwhile, four epidemiologists and 15 public health nurses were dispatched to interview 60 residents who had become ill or had contact will ailing residents.
The outbreak is confined to The Sequoias and is not a threat to the general population, Stebbins stressed.
The Sequoias is owned by Northern California Presbyterian Homes and Services, a nonprofit group that owns seven other retirement facilities, all but one in the Bay Area. But none of the firm's other entities, including a San Francisco complex also called The Sequoias, has been affected by the outbreak, said Mel Matsumoto, vice president of operations.
"Good people from public health are in place, doing what they need to do, '' Matsumoto said. "And we are cooperating fully because we want to get to the bottom of this as well."
Of the seven hospitalized, three have already been released, Stebbins said. A total of 17 residents and seven employees at the facility have been stricken, but none of the workers appeared to have required hospitalization. The first resident was hospitalized Friday.
Stebbins did not have details about the senior in critical condition at Stanford University Medical Center or the conditions of the other three patients who are being treated at local hospitals.
Two of the hospitalized seniors had confirmed cases of the E. coli 0157 strain. State health officials are expected to confirm by this afternoon whether the outbreak was triggered by the virulent E. coli sub-strain, 0157:H7,
which kills an estimated 61 Americans annually.
"In the U.S., the H7 variety tends to be the most common cause of this type of outbreak," Stebbins said.
State officials will also eventually be able to provide a genetic "snapshot'' of bacteria samples from the Portola Valley cases that will allow them to tell whether it's related to a larger Southern California E. coli outbreak, where contaminated lettuce served at restaurants sickened at least 36 people, Stebbins said.
"We don't think it's related,'' Stebbins added. "The state has done a lot of tracking on that Southern California outbreak and none of the products appear to reach Northern California."
A Mill Valley second-grader is recovering in a San Francisco hospital from an apparent bout with E. coli. The child was hospitalized a week ago with symptoms of the disease, which can cause severe cramping, bloody diarrhea and kidney damage.
E. coli illnesses have become surprisingly common since the bacterium was discovered in 1982. According to the federal Centers for Disease Control and Prevention, it strikes an estimated 73,000 Americans each year. The 0157:H7 strain kills about 61 people a year.
The bacteria is typically spread through ground beef and other food contaminated by cattle manure in food processing or by poor hygiene, when food handlers don't wash their hands properly, Stebbins said. The best prevention is thoroughly cooking beef, rinsing vegetables and washing hands prior to food preparation.
Contact Alan Gathright at agathright@sfchronicle.com.