A high school environmental science experience went awry when 29 students became infected with a lesser-known strain of pathogenic E. coli from the white-tailed deer they hunted, butchered and barbecued for a class project.
The incident, which happened more than a year ago, came to the media’s attention for the first time Wednesday, when the Centers for Disease Control and Prevention (CDC) published a study on the outbreak written by researchers at the Minnesota Department of Health.
In late November, 2010, two students from the environmental science class were admitted to their local hospital with bloody diarrhea. They shared the same doctor, who suspected their concurrent symptoms might indicate E. coli O157:H7 infections.
When both students tested negative for O157, the doctor called the Minnesota Department of Health, whose epidemiologist, Joshua Rounds, discovered that both students were infected with E. coli O103:H2, another Shiga toxin-producing strain and one of the “Big Six” non-O157 strains soon to be regulated by the U.S. Department of Agriculture in ground beef. Rounds served as lead author on the study published by the CDC.
It didn’t take long for the health department to trace back the infections to school barbeques where more than 200 students learned to field dress deer and help a professional butcher chop chunks of venison into kabob pieces. Students were also largely responsible for cooking their own meat, which was cut from one of seven deer, at least one of which carried E. coli O103, as well as O145:NM, a nonvirulent strain.
Through interviews, the health department found that 27 other students had diarrhea in the days following the barbeque.
Rounds said that the students could have become infected a number of ways, most likely from cross-contamination when handling the raw venison. Many of the infected students likely did not wash either their hands, plates or the tongs that touched contaminated meat.
One unique theory from the study was that the skewers used for the kabobs could have transferred E. coli from the surface of the meat into the center of the venison chunks, which may have been undercooked. So-called whole meats, such as steak cuts, are typically considered safe to eat rare because pathogens cannot penetrate the inner tissues, and will be killed when cooked, but kabob skewers might carry the bacteria inside the meat.
“This incident is another reminder of the standard food safety messages, but we decided to write about it because it’s a rarer case from a non-O157 Shiga toxin E. coli,” Rounds told Food Safety News.
Rounds said the public was not alerted to the outbreak because health department officials knew it was an isolated incident, and they had direct contact with the teachers, students and their families who were affected.
Some students took home leftover chunks of meat. The health department said samples from two homes tested positive for O103. The families were told how to handle and cook the meat properly, and advised to eat it at their own risk.
The two hospitalized students recovered and did not suffer from hemolytic uremic syndrome (HUS), a potentially fatal complication that arises from severe E. coli infections.
Rounds said that the students’ teachers expressed regret for not better supervising the cookout, but no one faced repercussions for the outbreak and illnesses. Since E. coli contamination comes from contact with feces, he suspected that the deer meat became contaminated either from a gut-piercing bullet wound or poor field dressing.
Studies on wild deer have shown the prevalence of E. coli O157 to range from 0.25 percent in Nebraska to 2.4 percent in Kansas. Non-O157 Shiga toxin-producing E. coli strains, including O103, have shown up in 5 percent of venison sampled in Minnesota and Wisconsin.