Category Archives: ecoli

E. coli O157:H7 Hazelnuts

Outbreak: E. coli O157:H7 Hazelnuts 
Product: HazelnutsInvestigation Start Date: 02/07/2011
Location: Multi-StateEtiology: E. coli (STEC) O157:H7
Earliest known case onset date: 12/20/2010Latest case onset date: 01/28/2011
Confirmed / Presumptive Case Count: 8 / 0Positive Samples (Food): 22

Eight outbreak cases of lab-confirmed E. coli O157:H7 were identified in Michigan, Minnesota, and Wisconsin. Initial, hypothesis generating interviews identified in-shell mixed nuts as a common exposure, specifically in-shell hazelnuts. A traceback investigation confirmed that the in-shell hazelnuts consumed by cases came from a common distributor which resulted in a press release and recall. Ultimately, the close collaboration between public health and agriculture agencies in multiple states, Centers for Disease Control and Prevention (CDC), and the United States Food and Drug Administration (FDA) allowed the identification of a novel vehicle for an O157 outbreak, with a very small number of detected cases.


A multi-state outbreak of E. coli O157:H7 infections associated with hazelnuts.


On February 7, 2011, the Minnesota Department of Health (MDH) Public Health Laboratory (PHL) determined that two human clinical E. coli O157:H7 isolates submitted through routine surveillance had indistinguishable PFGE patterns. A review of the national PulseNet database revealed four additional human E. coli O157:H7 isolates with the outbreak PFGE pattern in two states (three in Wisconsin and one in Michigan). A multi-state investigation was initiated.


Eight cases from three states were ultimately identified in this outbreak Minnesota (3), Wisconsin (4), and Michigan (1). All three Minnesota cases were male and had a median age of 62 years (range, 55 to 64 years). All three cases reported experiencing bloody diarrhea and cramps, two (66%) reported fever, one (33%) reported vomiting, and none reported fever. Two cases were hospitalized, each for 3 days. No cases developed hemolytic uremic syndrome and none died.
Upon initial interview, the first two Minnesota cases both reported consuming ground beef, sausage, lettuce, and nuts during the week prior to illness onset. Specific exposure information (i.e., brand and purchase location) collected on the ground beef, sausage, and lettuce consumed by the cases indicated these items were not from a common source. Upon re-interviews, all eight cases in the three states reported consuming in-shell hazelnuts also called filberts. Four case reported consuming hazelnuts as part of mixed nuts, and seven case reported purchased hazelnuts from bulk bins at grocery stores. One Wisconsin case reported purchasing packaged in-shell hazelnuts. However, further investigation at the grocery store where this product was purchased revealed that these hazelnuts were re-packaged at the store after originally being sold from a bulk bin.
A traceback investigation conducted by the Minnesota Department of Agriculture (MDA), in conjunction with the Michigan Department of Agriculture, California Food Emergency Response Team (CAL-FERT), and Wisconsin Department of Agriculture, Trade and Consumer Protection (WDATCP) found that the mixed nuts and in-shell hazelnuts purchased by cases originated from a single distributor, DeFranco and Son’s of California. On March 4, DeFranco and Sons issued a voluntary recall of all hazelnuts and mixed nut products distributed from November 2 through December 22, 2010. Recalled product was distributed to stores in seven states (Minnesota, Iowa, Michigan, Montana, North Dakota, South Dakota, and Wisconsin). A press release was issued on March 4, 2011 to inform the public.
In-shell hazelnuts collected by MDA from a case patient’s home tested positive for the outbreak PFGE subtype of E. coli O157:H7 on March 3, 2011. Additional mixed nut samples that included hazelnuts collected from recalled retail product by WDATCP and collected from DeFranco and Son’s by CAL-FERT also tested positive for the outbreak PFGE subtype of E. coli O157:H7. DeFranco and Son’s received hazelnuts from two companies in Oregon but did not maintain internal product traceability. The FDA conducted inspections of the two Oregon companies.


This was a multi-state outbreak of E. coli O157:H7 infections associated with eating in-shell hazelnuts grown in Oregon. Rapid collaboration between multiple state health departments and state departments of agriculture were crucial in identifying in-shell hazelnuts as the vehicle. This is the first documented outbreak of E. coli O157:H7 infections associated with nuts.

Raw Flour E. coli

Outbreak: Raw Flour E. Coli 
Product: Raw FlourInvestigation Start Date: 6/1/2016
Location: MultistateEtiology: E. coli O121
Earliest known case onset date: 12/21/2015Latest case onset date: 9/5/2016
Confirmed Case Count: 63Positive Environmental Samples: 39
Hospitalizations: 17Deaths: 0

CDC worked with public health and regulatory officials in many states and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Shiga toxin-producing Escherichia coli (STEC) infections.

Public health investigators used the PulseNet system to identify illnesses that may be part of this outbreak. PulseNet, coordinated by CDC, is the national subtyping network of public health and food regulatory agency laboratories. PulseNet performs DNA fingerprinting on STEC bacteria isolated from ill people by using techniques called pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). CDC PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks.

Sixty-three people infected with the outbreak strains of STEC O121 or STEC O26 were reported from 24 states. A list of the states and the number of cases in each can be found on the Case Count Map page. WGS showed that isolates from ill people were closely related genetically. This close genetic relationship means that people in this outbreak were more likely to share a common source of infection.

Illnesses started on dates ranging from December 21, 2015 to September 5, 2016. Ill people range in age from 1 year to 95, with a median age of 18. Seventy-six percent of ill people were female. Seventeen ill people were hospitalized. One person developed hemolytic uremic syndrome, a type of kidney failure, and no deaths were reported.


Flour is a raw, minimally processed product intended to be cooked before consumption. Although several previous Shiga-toxin-producing E. coli (STEC) outbreak investigations in the United States suspected contaminated flour as the source, none had been proven. In February 2016, PulseNet, the laboratory network for foodborne disease surveillance, detected a 12-state cluster of STEC O121 infections having the same rare genetic fingerprint. A multistate outbreak investigation was initiated. An additional STEC O26 strain was linked to the outbreak after testing of implicated flour.

A case was defined as infection with an outbreak strain of STEC O121 or O26 occurring between December 21, 2015, and September 5, 2016. Case-patients were interviewed about foods and other exposures in the week before illness onset. We performed univariable matched exact conditional logistic regression to identify exposures associated with illness, comparing them to exposures among people with reportable non-STEC enteric infections (primarily salmonellosis and campylobacteriosis), matched on age, gender, and state of residence. Four controls were sought for each case and interviewed by state and local health officials. Samples of suspected products were collected and cultured for STEC. A common point of contamination was sought through traceback. Whole genome sequencing (WGS) was performed on selected clinical and food isolates.

Fifty-six cases of STEC O121 and one case of STEC O26 infection were identified in 24 states; seventeen people were hospitalized; none died. Using General Mills flour (OR 21.0, 95% CI 4.7‒94.4) and tasting unbaked homemade dough or batter (OR 36.0, 95% CI 4.6‒280.2) were both significantly associated with illness. Traceback identified a common flour production facility. Three illnesses were in children exposed to raw dough for playing at several locations of a single restaurant chain. Leftover flour samples collected from cases’ homes and additional samples collected from the flour producer were tested, and five STEC strains were isolated (one STEC O26, three STEC O121, and one STEC O103). All isolates tested were closely related genetically.

This is the first investigation to link definitively an outbreak of STEC infections to raw flour. Nearly 250 products containing the implicated flour were recalled by the flour producer as well as by several companies that used recalled flour. Consumers should not eat products containing uncooked flour. Using uncooked dough for play should also be discouraged at restaurants and home. Flour producers should consider adding prominent packaging labels to warn consumer not to eat undercooked or raw flour. Foodborne illnesses associated with raw flour are likely preventable if appropriate control measures are taken from grain fields and production facilities to restaurants and consumers.

Publication citation: Crowe SJ., et al. Shiga toxin–producing E. coli infections associated with flour. New Engl J Med 2017; 377: 2036n43.