Assessing Differences in Risk Factors for O157 and Non-O157 Shiga Toxin-Producing Escherichia coli in Florida

BACKGROUND:  While O157:H7 Shiga Toxin-Producing Escherichia coli (STEC) infection remains a well-known cause of severe, bloody diarrhea and hemolytic-uremic syndrome (HUS), non-O157 STEC infections are increasingly recognized as the majority contributors to this disease burden. Advances in laboratory technologies and surveillance practices, as well as documented outbreaks of non-O157 STEC infection, have increased conventional knowledge about these historically underrepresented serogroups. In an effort to further understand its burden of STEC infections, the Florida Department of Health (FDOH) assessed the differences in risk factors for O157 and non-O157 STEC infections.

METHODS:  Data from STEC infection case reports and laboratory results are entered into the web-based reportable disease surveillance system (Merlin). In June 2009, fields were added to Merlin to electronically capture risk factor data from Florida’s standardized paper STEC case report form. Data collected from June 1, 2009 to May 31, 2013 were reviewed.

RESULTS:  From June 1, 2009 to May 31, 2013, a total of 347 laboratory-confirmed STEC infection cases were reported in Florida, of which 315 (91%) were interviewed. A total of 237 primary, Florida-acquired cases were reviewed, with 117 (49%) of those cases infected with a non-O157 serogroup. The most common risk factors reported for both O157 and non-O157 STEC were: consuming or handling meat products (42% for O157, 38% for non-O157), consuming raw fruits/vegetables (35% for O157, 33% for non-O157), consuming food at/from a restaurant (31% for O157, 24% for non-O157), and having contact with animals (27% for O157, 18% for non-O157). Observed differences in O157 and non-O157 STEC risk factors were not statistically significant.  Differences in incidence and exposures for O157 and non-O157 STEC infections for 237 primary, Florida-acquired infections by age, gender, race, ethnicity, and season will be presented.

CONCLUSIONS: Significant differences in risk factors for O157 and non-O157 STEC infections were not detected, and changes to current preventive actions are not recommended at this time. As laboratory testing capabilities expand, and increased numbers of non-O157 STEC are laboratory confirmed, FDOH anticipates that better characterization of O157 versus non-O157 STEC risk factors will be possible. The identification of meaningful differences in risk factors associated with O157 and non-O157 STEC would allow prevention education to be tailored at the serogroup level. While FDOH works to turn these expectations into reality, current STEC surveillance continues to aid epidemiologists in identifying STEC outbreaks and guiding those outbreak investigations.