Thirty-three E. coli infections are being studied; 24 cases have been confirmed by the state laboratory.
Determining whether the infecting bacteria are the same genetic strain will solve a key mystery of the outbreak and help investigators determine which of the cases are related so they can begin tracing the source.
The most common link among the people who are sick is a trip to the State Fair last month -- in particular, to a petting zoo exhibit. Of the 33 cases under scrutiny, 15 have State Fair connections, one attended the Cleveland County fair, seven did not attend the fair and the remainder have not completed the investigator's questionnaire.
"If it does turn out to be a petting zoo, there are thousands of people who were exposed, and they are widespread," said Dr. Jeffrey Engel, state epidemiologist. "People came to visit from other states."
Engel said he has alerted his counterparts in other states through an electronic posting and is working with officials from the Centers for Disease Control and Prevention. Four CDC investigators have joined dozens of state and county health officials working to track the outbreak and prevent further spreading.
Quarantining the animals in the suspected petting zoos, however, has not been done. One of the petting zoos headed to a fair in South Carolina; the other is a North Carolina farm and only does a few fairs a year.
"For the petting zoo industry, this is a risk wherever they are," Engel said.
The type of E. coli that has sickened the North Carolina people is common in cattle, goats and sheep. It causes the animals no harm but is dangerous to humans, causing severe diarrhea and possible kidney damage.
"The measure is not to quarantine the animals, the measure is to provide information and prevention strategies," Engel said.
Hand-washing is the most effective means of avoiding an E. coli infection, and the petting zoos had posted numerous hand-washing stations at its exhibits. In Pennsylvania, Engel said, petting zoos are required by law to have hand-washing stations along with posters explaining the risks of bacterial infections.
"Maybe with this outbreak, it'll become a law in North Carolina, too," Engel said.
Most of the people infected by the bacteria are children. Two patients, including a 13-year-old girl from Moore County, have developed a severe complication known as hemolytic-uremic syndrome, in which the number of blood platelets suddenly drops, red blood cells are destroyed and the kidneys shut down.
The Moore County girl, Katie Maness, has been transferred to UNC Hospitals in Chapel Hill, said her mother, Becky Maness, on Wednesday. The syndrome can be life-threatening or cause permanent kidney damage.
The outbreak is North Carolina's largest E. coli infection since a 2001 incident in Robeson County that stemmed from unpasteurized butter offered to schoolchildren during a demonstration. More than 200 grew sick.
Food contamination, particularly from beef that has come in contact with animal feces during slaughter and processing, is often the source of E. coli infections, but petting zoos are also common sources.
William Marler, a Seattle lawyer who has built a national practice filing lawsuits in E. coli and other contamination cases, said petting zoos are aware of the dangers of the business, and most provide hand-washing stations. But even the best of precautions can still fall short.
He said he represented 25 families in an unsuccessful Oregon case in which people grew ill after visiting the petting zoo. Half of the victims washed their hands; half didn't. Babies in strollers got sick despite never getting out of their strollers or touching the animals.
"The frustrating thing was, there wasn't a common denominator," Marler said. "We were trying to figure out what the fair did or should've done to prevent the outbreak."
He said two of the North Carolina families in the current outbreak have called him, but he does not know whether there is a legal case. Much depends on what state health investigators turn up and whether the outbreak is traced to the State Fair.
"When I was a kid taking my cow to the fair, nobody even heard of E. coli," Marler said. "That was 35 years ago. But since Jack in the Box, and with repeated fair outbreaks, we have to be more vigilant."