Lessons in surveillance: a four-state outbreak of E. coli infections from fast food hamburgers

Repercussions of 1992-1993 outbreak in the western United States still reverberate today.

A combination of prompt reporting and the use of pulsed field gel electrophoresis aided public health officials in stemming the tide of an Escherichia coli O157:H7 outbreak in the western United States in 1992-1993. Experts believe that the subsequent recall of approximately 250,000 hamburger patties may have saved as many as 800 people from illness.

The outbreak infected 732 people, most of whom were children; 25% of those infected were hospitalized. More than 7% of those infected developed hemolytic uremic syndrome, and four children died.

The Washington experience

The investigation began on Jan. 12, 1993, when a pediatric gastroenterologist notified the Washington Department of Health that ED visits for bloody diarrhea had sharply increased and that three children with hemolytic uremic syndrome had been admitted to Children’s Hospital and Medical Center in Seattle.

Patricia M. Griffin, MD, was a member of the Foodborne and Diarrheal Diseases Branch of the National Center for Infectious Diseases at CDC when the outbreak occurred. “At that time, E. coli O157 was a notifiable disease in Washington state,” she said in an interview with Infectious Disease News. “This was not the case for most other states. As a result, clinicians in Washington were perhaps more aware of this pathogen than were clinicians in other parts of the country.”

By Jan. 15, 1993, the Washington Department of Health had begun active surveillance for outbreak-related illnesses. Through use of a standard questionnaire with questions targeting specific meals within 10 days before the illness began, investigators quickly determined that hamburgers from Jack in the Box chain restaurants were the source of the illnesses.

A case-control study was conducted on Jan. 16 and 17, 1993. The results demonstrated that regular-sized hamburgers, which weighed approximately 46 g and were popular with children, had been consumed by most of the people who became infected.

On Jan. 17, 1993, health department officials visited 10 Jack in the Box restaurants to collect raw hamburger patties for cooking and culture.

Prior to the outbreak, FDA recommendations required hamburgers be cooked to an internal temperature of 60° C. During the investigation, health officials determined that a temperature of 68.3° C was necessary to kill 99% of organisms. As the outbreak unfolded, the FDA raised the recommended temperature to meet this standard, according to Griffin.

On Jan. 18 and 19, 1993, investigators cooked hamburgers according to Jack in the Box specifications and determined that, even after heating, at least one internal temperature measurement often was below 68.3° C (range: 41.7° C to 81.1° C).

Hidden epidemic

Following a public announcement on Jan. 18, 1993, reports of the disease increased dramatically. The health department in Washington received dozens of calls from concerned individuals and parents of infected children. “People were shocked that the responsibility of killing pathogens lay in their own hands or in the hands of restaurant employees,” Griffin said, remembering common questions raised by parents. “‘There is something in meat that can kill my child? And it is my job to kill it?’”

The public outcry may have helped prevent illness in other parts of the country where incidence of E. coli was on the rise.

Prior to the 1992-1993 outbreak, the major private laboratory in Las Vegas had ceased testing for E. coli due to the cost. On Jan. 21, 1993, the parent of a child with bloody diarrhea in Las Vegas had heard about the outbreak in Seattle and called a pediatrician. The pediatrician then called the health department to inquire about the possibility of an outbreak in Las Vegas. “That same day, another health department official in the city was driving by one of the chain’s restaurants and saw that hamburger patties were being removed,” Griffin said. “Though no confirmed cases had been reported up to that point, the Las Vegas health department placed an ad in the newspaper encouraging anyone with bloody diarrhea to contact them immediately. They were flooded with calls.”

An action plan of case-control studies and environmental and laboratory investigations similar to the one in Washington was enacted.

Between December 1992 and January 1993, 58 individuals in Las Vegas had bloody diarrhea, and three of those patients developed hemolytic uremic syndrome.

During the same period, there were 32 infections in southern California and 13 infections in Idaho.

Laboratory, slaughterhouse

Kathleen F. Gensheimer, MD, MPH, is the state epidemiologist in the medical epidemiology section in the division of infectious diseases at the Maine Department of Health and Human Services and an Infectious Disease News Editorial Board member. She said that this outbreak demonstrated the importance and effectiveness of using pulsed field gel electrophoresis in public health surveillance activities. “Genetic fingerprinting really allowed them to pinpoint a lot of the cases across the four states,” she said. “It is a great tool, but it was not widely used then. They were fortunate to have those isolates tested with this newly-available public health tool.”

Having access to the isolates benefitted all aspects of the investigation, from the clinic to the slaughterhouse.

Trace-backs led the investigators to plants which used a process called bed slaughter. This method involves the slain animal lying on a bed of rails a few inches above a floor that was often covered with feces and dirt, according to Griffin. Slaughterhouse workers then skinned the animals by hand.

The skinned carcasses were sent to boning plants, where the meat was removed on a long table and placed on a conveyor belt. Department of Agriculture officials conducted visual inspections only. The conveyor belts were sanitized just once a day. “Unfortunately, despite our best efforts, as far as sanitation goes, the slaughterhouse quite simply is not the operating room,” Gensheimer said.

Although investigators were able to trace the contaminated meat back to the boning plant that was the sole supplier of frozen hamburgers to Jack in the Box restaurants, they were unable to accurately trace the meat back to its original source. In fact, it had likely come from both domestic and international sources, highlighting the fact that any given hamburger can contain meat from several locations around the world.

Legacy

The inability of investigators to trace the meat back to its source due to the increasingly complex globalized production system marked the beginning of a paradigm shift in the approach to surveillance of foodborne illnesses. Griffin, who is now chief of enteric diseases epidemiology branch in the division of foodborne, bacterial, and mycotic diseases at the National Center for Zoonotic, Vectorborne, and Enteric Diseases at CDC, said that the effect of this outbreak was “a watershed for meat safety in the United States.”

The low infectious dose of the pathogen had been a major concern. “The minimum infectious dose of this disease may be as low as 20 organisms per gram,” Griffin said.

Griffin said that soon after this investigation, the USDA declared E. coli O157 to be an adulterant in ground beef. In addition, USDA implement a pathogen reduction program called Hazard Analysis and Critical Control Points in beef plants. The program includes zero tolerance for fecal matter on cattle carcasses and culturing for Salmonella, which is another common contaminant that causes human illness.

The impact of the outbreak on the general public also cannot be underestimated. “This outbreak made E. coli a household word,” Griffin said. “It brought food safety into the homes of average Americans, and into Congress. From a public health perspective, this has been extremely influential.”

Gensheimer summed up the effect of the investigation in terms of industry distribution, public health and public perception. “E. coli used to be a hamburger disease, but that is no longer the case,” she said. “Since then, we have seen this organism transmitted from multiple foods, including sprouts, apple cider, lettuce, spinach and fruit juices.”– by Rob Volansky

For more information:

• Bell B. et al. JAMA.1994;272:1349-1353.
• Cieslak P. et al. Am J Public Health.1997;87:176-180.
• Griffin P. et al. Large Outbreak of Escherichia coli O157:H7 Infections in the Western United States: The Big Picture. Recent advances in verocytotoxin-producing Escherichia coli Infections. Proceedings of the 2nd International Symposium and Workshop on Verocytotoxin (Shiga-like toxin)-producing Escherichia coli infections, Bergamo, Italy, June 1994. New York:Elsevier, 1994:7-12.
• Shefer A. et al. West J Med. 1996; 165:15-19.