Today’s Morbidity and Mortality Weekly Report (MMWR) contains “Recommendations for Diagnosis of Shiga Toxin–Producing Escherichia coli Infections by Clinical Laboratories.”  The report, which was written by collaborators from federal and state government agencies, universities, and private organizations, focuses on improving our public health response to Shiga toxin-producing E. coli (STEC) outbreaks in the United States by improving processes by which laboratories process STEC cultures and report them to the proper public health agencies.

lab-testing.jpgAccording to the most recent estimates, STEC cause approximately 100,000 illnesses, 3,000 hospitalizations, and 90 deaths annually in the United States.  The majority of those illnesses are caused by E. coli O157:H7, but non-O157 STEC have also been associated with foodborne illness in the United States. 

E. coli O111 was the source of a 2008 E. coli outbreak in Oklahoma, and E. coli O121 was the source of a 2006 E. coli outbreak in Utah.  Other known STEC serogroups include O26, O45, O103, and O145. 

The Shiga toxin produced by these E. coli serogroups causes acute, often bloody, diarrhea in individuals who have ingested STEC bacteria.  Hemolytic uremic syndrome (HUS) is a life-threatening condition that can result from E. coli infection, and can cause kidney failure, central nervous system damage, and other complications in otherwise healthy individuals.   

STEC can be present on a wide variety of foods.  Known outbreaks have occurred due to contamination of ground beef, unpasteurized juice, raw milk, raw produce, and other foods.  In addition, STEC can be transmitted through contact with animals or from other infected people. 

The article’s authors recommend “that all stools submitted for routine testing from patients with acute community-acquired diarrhea (regardless of patient age, season of the year, or presence or absence of blood in the stool) be simultaneously cultured for E. coli O157:H7 (O157 STEC) and tested with an assay that detects Shiga toxins to detect non-O157 STEC.” And state, “The recommendations are intended primarily for clinical laboratories but also are an important reference for health-care providers, public health laboratories, public health authorities, and patients and their advocates.”

Benefits of the recommended testing strategy identified by the article’s authors include:

  • Identification of additional STEC infections and detection of all STEC serotypes
  • Early diagnosis and improved patient outcome
  • Prompt detection of outbreaks

Procedures for collecting and handling specimens for STEC diagnostic testing, culturing STEC, the use of nonculture assays for detection of Shiga toxins and STEC, specialized diagnostic methods for lab personnel, procedures for forwarding specimens and isolates to public health labs, the interpretation of final lab results, and clinical considerations are all included in the MMWR. 

The authors conclude, “These recommendations should improve the accuracy of diagnosing STEC infections, facilitate assessment of risk for severe illness, promote prompt diagnosis and treatment, and improve detection of outbreaks.

“Because of the critical impact of time on diagnosis of STEC, treating patients, and recognizing and controlling outbreaks of STEC infections, attempting to isolate O157 STEC and detect other STEC serotypes simultaneously, rather than separately (i.e., conducting a Shiga toxin test to determine whether to culture), is recommended. Performing culture for O157 STEC while simultaneously testing for all STEC serotypes is critical. . . .  Detection of O157 STEC within 24 hours after specimen submission to the laboratory helps physicians to rapidly assess the patient’s risk for severe disease and to initiate measures to prevent serious complications, such as renal damage and death. Rapid isolation of the infecting organism helps public health officials quickly initiate measures to detect outbreaks and control the spread of infection.”

E. coli O157:H7 was declared an adulterant in meat in 1994.  A recent petition filed with the U.S. Department of Agriculture (USDA)’s Food Safety and Inspection Service asks the USDA to declare all STEC adulterants under the Federal Meat Inspection Act.  (See Lawyers Petition USDA on E. coli Issue, Oct. 6 and USDA Should Declare non-O157 E. coli an Adulterant, Oct. 5)

Photo courtesy CDC/ Hsi Liu, Ph.D., MBA, James Gathany.