Notes from the Field: Multistate Outbreak of Escherichia coli O157:H7 Infections Linked to Dough Mix — United States, 2016
Weekly / January 27, 2017 / 66(3);88–89
Laura Gieraltowski, PhD1; Colin Schwensohn, MPH1; Stephanie Meyer, MPH2; Dana Eikmeier, MPH2; Carlota Medus, PhD2; Alida Sorenson, MPH3; Matthew Forstner3; Asma Madad, MS, MPH4; Joseph Blankenship, MPH4; Peter Feng, PhD4; Ian Williams, PhD1 (View author affiliations)View suggested citation
Views equals page views plus PDF downloads
- pdf icon [PDF]
On January 4, 2016, CDC PulseNet, the molecular subtyping network for foodborne disease surveillance, identified a cluster of 10 Shiga toxin-producing Escherichia coli (STEC) O157:H7 infections with indistinguishable pulsed-field gel electrophoresis (PFGE) pattern combinations. STEC infections with the identified outbreak PFGE pattern are commonly reported to PulseNet, with an average of 40–50 illnesses reported annually. Because this was a relatively common strain of STEC, multiple locus variable-number tandem repeat analysis (MLVA), another subtyping technique used to characterize the genetic relatedness of bacteria, was used to help define cases in the cluster. CDC collaborated with state and local health and agricultural agencies and the Food and Drug Administration (FDA) to investigate the outbreak. A case was defined as STEC O157:H7 infection with an isolate having PFGE and MLVA patterns indistinguishable from the outbreak strain in a person with diarrheal illness onset during December 6, 2015–February 9, 2016.
Thirteen STEC O157:H7 outbreak-associated cases were identified in nine states: Iowa (one case), Illinois (one), Kansas (one), Minnesota (five), North Carolina (one), Nebraska (one), New Jersey (one), South Dakota (one), and Wisconsin (one). The median age of patients was 17 years (range = 7–71 years); 53% were female. Among 12 patients with available information, eight were hospitalized, including two who developed hemolytic uremic syndrome; no deaths were reported.
Among the 12 interviewed patients, nine reported eating at one of nine locations of restaurant A, a national restaurant chain, during the week preceding illness onset, including eight who ate a specific dessert pizza made with a proprietary dough mix provided by manufacturer A. The ninth patient consumed bread sticks made from the same dough mix. At one Minnesota location, six of 21 (28%) non-ill patrons reported eating the implicated dessert pizza. Assuming this was representative of patrons of restaurant A, the proportion of cases who consumed dessert pizza was significantly higher than what would be expected by chance using the binomial distribution model (p<0.001). As an intervention in this outbreak, restaurant A locations stopped using dough mix from manufacturer A on February 4, 2016.
Eighty-eight samples of dry dough mix from five restaurant A locations where patients reported eating were collected by public health officials in five states (Illinois, Iowa, Minnesota, Nebraska, and Wisconsin). The Minnesota Department of Agriculture identified non-O157 STEC in seven of 17 collected samples, including one Shiga toxin-1–producing non-O157 STEC isolate and six Shiga toxin-2 (stx2)–producing non-O157 STEC isolates. FDA collected six samples of dry dough mix from manufacturer A. All six samples tested negative for STEC O157:H7, but one yielded an stx2-producing STEC O8:H28. All identified strains lacked known adherence factors and were therefore considered to present a low health risk.
Flour is a raw agricultural product and does not undergo processing to kill bacteria and other pathogens, so it is not sterile. Generic E. coli and coliforms have been found previously in flour (1,2). Flour and flour-based mixes have been suspected or implicated as the source of other foodborne Salmonella and STEC O157 outbreaks (1,3–6). Of note, this PFGE pattern was previously isolated from a sample of bulk flour collected during a 2009 outbreak investigation (5). Although no laboratory evidence identified contaminated flour as the ultimate source of this STEC O157:H7 outbreak, the identification of other enteric pathogens in multiple samples of dry dough mix consumed by patients associated with the outbreak implicates contaminated flour as the possible source of pathogen introduction for this outbreak. The small number of cases and the lack of additional restaurant clusters suggest that this was a low level contamination event or that contamination only affected a limited amount of product. Evidence obtained at one restaurant A location showed that dessert pizzas were made with the same dough mix used in traditional pizzas, but used thicker dough and might have been undercooked at some locations. Flour is usually not thought to be a food safety risk, but flour-based mixes are ubiquitous in restaurants and are often used for dusting of surfaces for transfer of pizzas. This outbreak serves as a reminder that consumers, industry, and government should consider that flour, a raw agricultural product, might be contaminated with pathogens and, when consumed raw or undercooked, might pose a risk to human health.
Kirk Smith, Kim Carlton, Nicole Hedeen, Samantha Olson, Vaishnavi Pattabiraman, Carrie Rigdon; Minnesota Department of Agriculture Microbiology Unit; Iowa Department of Public Health; Iowa Department of Inspection and Appeals; University of Iowa Hygienic Laboratory; Illinois Department of Public Health (IDPH); IDPH Springfield Environmental Micro Laboratory; Tazewell County Health Department, Illinois; Kansas Department of Health & Environment; North Carolina Department of Health and Human Services; Nebraska Department of Health and Human Services; Ohio Department of Health; Pennsylvania Department of Health; South Dakota Department of Health; Tennessee Department of Human Services; Wisconsin Division of Public Health; Wisconsin Department of Agriculture, Trade and Consumer Protection Bureau of Laboratory Services; Food and Drug Administration, Kansas City District Office, Missouri.
Corresponding author: Laura Gieraltowski, LGieraltowski@cdc.gov,404-639-3868.
- New Zealand Food and Safety Authority. Flour batch believed linked to Salmonella outbreak. Wellington, NZ: New Zealand Food and Safety Authority; 2008. http://foodsafety.govt.nz/elibrary/industry/Flour_Batch-Investigations_Into.htmexternal icon
- Sperber WH; North American Millers’ Association Microbiology Working Group. Role of microbiological guidelines in the production and commercial use of milled cereal grains: a practical approach for the 21st century. J Food Prot 2007;70:1041–53. CrossRefexternal icon PubMedexternal icon
- Zhang G, Ma L, Patel N, Swaminathan B, Wedel S, Doyle MP. Isolation of Salmonella typhimurium from outbreak-associated cake mix. J Food Prot 2007;70:997–1001. CrossRefexternal icon PubMedexternal icon
- Richter KS, Dorneanu E, Eskridge KM, Rao C. Microbiological quality of flours. Cereal Foods World 1993;38:367–9.
- Neil K, Biggerstaff G, MacDonald K, et al. A novel vehicle for transmission of Escherichia coli O157:H7 to humans: multistate outbreak of E. coli O157:H7 infections associated with consumption of ready-to-bake commercial prepackaged cookie dough—United States, 2009. Clin Infect Dis 2012;54:511–8. CrossRefexternal icon PubMedexternal icon
- CDC. Multistate outbreak of Shiga toxin-producing Escherichia coli infections linked to flour. Atlanta, GA: US Department of Health and Human Services, CDC; 2016. https://www.cdc.gov/ecoli/2016/o121-06-16/index.html
Suggested citation for this article: Gieraltowski L, Schwensohn C, Meyer S, et al. Notes from the Field. Multistate Outbreak of Escherichia coli O157:H7 Infections Linked to Dough Mix — United States, 2016. MMWR Morb Mortal Wkly Rep 2017;66:88–89. DOI: http://dx.doi.org/10.15585/mmwr.mm6603a6external icon.
MMWR and Morbidity and Mortality Weekly Report are service marks of the U.S. Department of Health and Human Services.
Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services.
References to non-CDC sites on the Internet are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites. URL addresses listed in MMWR were current as of the date of publication.
All HTML versions of MMWR articles are generated from final proofs through an automated process. This conversion might result in character translation or format errors in the HTML version. Users are referred to the electronic PDF version (https://www.cdc.gov/mmwr) and/or the original MMWR paper copy for printable versions of official text, figures, and tables.
Questions or messages regarding errors in formatting should be addressed to firstname.lastname@example.org.