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Shiga toxin-producing Escherichia coli (STEC) cause substantial and costly illnesses. Leafy greens are the second most common source of foodborne STEC O157 outbreaks. We examined STEC outbreaks linked to leafy greens during 2009-2018 in the United States and Canada. We identified 40 outbreaks, 1,212 illnesses, 77 cases of hemolytic uremic syndrome, and 8 deaths. More outbreaks were linked to romaine lettuce (54%) than to any other type of leafy green. More outbreaks occurred in the fall (45%) and spring (28%) than in other seasons. Barriers in epidemiologic and traceback investigations complicated identification of the ultimate outbreak source. Research on the seasonality of leafy green outbreaks and vulnerability to STEC contamination and bacterial survival dynamics by leafy green type are warranted. Improvements in traceability of leafy greens are also needed. Federal and state health partners, researchers, the leafy green industry, and retailers can work together on interventions to reduce STEC contamination. [ABSTRACT FROM AUTHOR]

Following infection with certain strains of Shiga toxin-producing Escherichia coli (STEC), particularly enterohemorrhagic ones, patients are at elevated risk for developing life-threatening extraintestinal complications, such as acute renal failure. Hence, these bacteria represent a public health concern in both developed and developing countries. Shiga toxins (Stxs) expressed by STEC are highly cytotoxic class II ribosome-inactivating proteins and primary virulence factors responsible for major clinical signs of Stx-mediated pathogenesis, including bloody diarrhea, hemolytic uremic syndrome (HUS), and neurological complications. Ruminant animals are thought to serve as critical environmental reservoirs of Stx-producing Escherichia coli (STEC), but other emerging or arising reservoirs of the toxin-producing bacteria have been overlooked. In particular, a number of new animal species from wildlife and aquaculture industries have recently been identified as unexpected reservoir or spillover hosts of STEC. Here, we summarize recent findings about reservoirs of STEC and review outbreaks of these bacteria both within and outside the United States. A better understanding of environmental transmission to humans will facilitate the development of novel strategies for preventing zoonotic STEC infection. [ABSTRACT FROM AUTHOR]

Shiga toxin–producing Escherichia coli (STEC) of serotype O113:H21 have caused severe diseases but are unusual in that they do not produce the intimin protein required for adherence to intestinal epithelial cells. Strains of serogroup O113 are one of the most common STEC found in ground beef and beef products in the United States, but their virulence potential is unknown. We used a microarray to characterize 65 O113 strains isolated in the United States from ground beef, beef trim, cattle feces, and fresh spinach. Most were O113:H21 strains, but there were also nine strains of O113:H4 serotype. Although strains within the same serotype had similar profiles for the genes that were tested on the array, the profiles were distinct between the two serotypes, and the strains belonged to different clonal groups. Analysis by clustered regularly interspaced short palindromic repeat analysis showed that O113:H4 strains are conserved genetically, but the O113:H21 strains showed considerable polymorphism and genetic diversity. In comparison to the O113:H21 strains from Australia that were implicated in severe disease, the U.S. isolates showed similar genetic profiles to the known pathogens from Australia, suggesting that these may also have the potential to cause infections. [ABSTRACT FROM AUTHOR]

Shiga toxin-producing Escherichia coli (STEC) causes acute diarrheal illness. To determine risk factors for non-O157 STEC infection, we enrolled 939 patients and 2,464 healthy controls in a case-control study conducted in 10 US sites. The highest population-attributable fractions for domestically acquired infections were for eating lettuce (39%), tomatoes (21%), or at a fast-food restaurant (23%). Exposures with 10%-19% population attributable fractions included eating at a table service restaurant, eating watermelon, eating chicken, pork, beef, or iceberg lettuce prepared in a restaurant, eating exotic fruit, taking acid-reducing medication, and living or working on or visiting a farm. Significant exposures with high individual-level risk (odds ratio >10) among those >1 year of age who did not travel internationally were all from farm animal environments. To markedly decrease the number of STEC-related illnesses, prevention measures should focus on decreasing contamination of produce and improving the safety of foods prepared in restaurants.

The U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) Chapter 4a describes a Luminex microbead-based suspension array used to screen colonies for 11 clinically relevant Shiga toxin-producing Escherichia coli (STEC) serogroups: 026, 045, 091, 0103, 0104, 0111, 0113, 0121, 0128, 0145, and 0157. We evaluated the usefulness of this method to identify STEC-positive enrichment samples before agar plating. Twelve E. coli strains were added to three types of fresh produce (bagged baby spinach, alfalfa sprouts, and cilantro) at levels near the detection limit of the test. A subset of these strains (six O serogroups) was similarly evaluated in raw milk. For comparison, portions of each of the 168 enrichment cultures were analyzed for serogroup by a real-time PCR assay and a Bio-Plex 200 assay with the bead-based suspensions. No falsepositive results were obtained. Of the 112 samples with a reported cycle threshold (CT) value, 101 undiluted, diluted, or extracted enrichment cultures also produced ratios above 5.0 in the Bio-Plex assay. When PCR CT values approached or were greater than 35, Bio-Plex detection became less reliable. Using undiluted or extracted enrichment cultures resulted in a significantly larger number of positive results. With the same enrichment material prepared for real-time PCR analysis as described in the BAM Chapter 4a, the STEC tnicrobead-based suspension array can accurately screen food enrichment cultures. [ABSTRACT FROM AUTHOR]

Foodborne outbreaks reported to national surveillance systems represent a subset of all outbreaks in the United States; not all outbreaks are detected, investigated, and reported. We described the structural factors and outbreak characteristics of outbreaks reported during 2009-2018. We categorized states (plus DC) as high (highest quintile), middle (middle 3 quintiles), or low (lowest quintile) reporters on the basis of the number of reported outbreaks per 10 million population. Analysis revealed considerable variation across states in the number and types of foodborne outbreaks reported. High-reporting states reported 4 times more outbreaks than low reporters. Low reporters were more likely than high reporters to report larger outbreaks and less likely to implicate a setting or food vehicle; however, we did not observe a significant difference in the types of food vehicles identified. Per capita funding was strongly associated with increased reporting. Investments in public health programming have a measurable effect on outbreak reporting.

Abstract: Several outbreaks of Shiga toxin-producing Escherichia coli infections in the past decade have been linked to flour and flour-associated products and have raised concerns that the consumption of raw flour represents a public health risk as a vehicle for foodborne pathogens. The extent to which consumers know and understand that they should not consume raw flour is unclear. In fall 2019, the U.S. Food and Drug Administration collected data on perceptions regarding uncooked flour and on self-reported consumption behaviors via the Food Safety and Nutrition Survey, a national probability survey of U.S. adults (≥18 years of age). Cross-tabulations and regressions were used to analyze the data (n = 2,171). Thirty-five percent of consumers reported having tasted or eaten something with uncooked flour in it in the previous 12 months. Responses differed significantly by sex, race, education, and age. On average, respondents indicated that uncooked flour is not likely to contain germs that can make people sick, with significant differences noted by demographic categories. Respondents rated raw homemade cookie dough as moderately likely to have germs that can make people sick, with significant demographic differences. These findings indicate that U.S. consumers are largely unaware that raw flour is risky to consume, and many people are consuming products that contain raw flour., (Published 2022 by the International Association for Food Protection. Not subject to U.S. Copyright.)

Abstract: Animals (grazing, working, or intrusion) in produce production areas may present a potential contamination source of foodborne pathogens on produce. Cattle grazing on native pecan production orchards, a common practice in the southern United States, provides an opportunity to study the impact of grazing practice and waiting periods on contamination rates of foodborne pathogens of tree nuts. Therefore, the objective of this study was to determine the prevalence of Salmonella and Shiga toxin-producing Escherichia coli (STEC) in native pecan production orchards as influenced by waiting periods between grazing cattle and pecan harvest. Soil (10 g), cattle feces (10 g), and in-shell pecans (25 g) were sampled from five cattle-grazed orchards in areas with cattle removed 2 or 4 months before harvest and not removed. Five nongrazing orchards were sampled at harvest for comparison. Detection and isolation of the pathogens were performed by enrichment, selective isolation, and multiplex PCR. Statistical analyses were performed using contingency tables with Pearson's chi-square test. The prevalence of STEC (36%) and Salmonella (29%) in cattle-grazed orchards was significantly higher than in nongrazed orchards (13 and 7%, respectively). STEC prevalence in cattle-grazed orchards was higher (38%) in areas with cattle at harvest than in fenced areas where cattle were removed 2 (29%) and 4 (27%) months before harvest. Salmonella prevalence was similar in areas without fencing (31%) and areas with cattle removed at 2 (22%) and 4 (30%) months before harvest. However, there were no significant differences (P > 0.05) in contamination rates between waiting periods for either pathogen, suggesting a limited impact of waiting periods on reducing the risk of contamination., (Copyright ©, International Association for Food Protection.)

Abstract: A total of 482 veal cutlet, 555 ground veal, and 540 ground beef samples were purchased from retail establishments in the mid-Atlantic region of the United States over a noncontiguous 2-year period between 2014 and 2017. Samples (325 g each) were individually enriched and screened via real-time PCR for all seven regulated serogroups of Shiga toxin-producing Escherichia coli (STEC). Presumptive STEC-positive samples were subjected to serogroup-specific immunomagnetic separation and plated onto selective media. Up to five isolates typical for STEC from each sample were analyzed via multiplex PCR for both the virulence genes (i.e., eae, stx1 and/or stx2, and ehxA) and serogroup-specific gene(s) for the seven regulated STEC serogroups. The recovery rates of non-O157 STEC from veal cutlets (3.94%, 19 of 482 samples) and ground veal (7.03%, 39 of 555 samples) were significantly higher (P < 0.05) than that from ground beef (0.93%, 5 of 540 samples). In contrast, only a single isolate of STEC O157:H7 was recovered; this isolate originated from 1 (0.18%) of 555 samples of ground veal. Recovery rates for STEC were not associated with state, season, packaging type, or store type (P > 0.05) but were associated with brand and fat content (P < 0.05). Pulsed-field subtyping of the 270 viable and confirmed STEC isolates from the 64 total samples testing positive revealed 78 pulsotypes (50 to 80% similarity) belonging to 39 pulsogroups, with ≥90% similarity among pulsotypes within pulsogroups. Multiple isolates from 43 (67.7%) of 64 samples testing positive had an indistinguishable pulsotype. STEC serotypes O26 and O103 were the most prevalent serogroups in beef and veal, respectively. These findings support related findings from regulatory sampling studies over the past decade and confirm that recovery rates for the regulated STEC serogroups are higher for raw veal than for raw beef samples, as was observed in the present study of meat purchased at food retailers in the mid-Atlantic region of the United States., (Published 2021 by the International Association for Food Protection. Not subject to U.S. Copyright.)

Provision of safe drinking water in the United States is a great public health achievement. However, new waterborne disease challenges have emerged (e.g., aging infrastructure, chlorine-tolerant and biofilm-related pathogens, increased recreational water use). Comprehensive estimates of the health burden for all water exposure routes (ingestion, contact, inhalation) and sources (drinking, recreational, environmental) are needed. We estimated total illnesses, emergency department (ED) visits, hospitalizations, deaths, and direct healthcare costs for 17 waterborne infectious diseases. About 7.15 million waterborne illnesses occur annually (95% credible interval [CrI] 3.88 million-12.0 million), results in 601,000 ED visits (95% CrI 364,000-866,000), 118,000 hospitalizations (95% CrI 86,800-150,000), and 6,630 deaths (95% CrI 4,520-8,870) and incurring US $3.33 billion (95% CrI 1.37 billion-8.77 billion) in direct healthcare costs. Otitis externa and norovirus infection were the most common illnesses. Most hospitalizations and deaths were caused by biofilm-associated pathogens (nontuberculous mycobacteria, Pseudomonas, Legionella), costing US $2.39 billion annually.

Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen that has a significant impact on public health, with strains possessing the attachment factor intimin referred to as enterohemorrhagic E. coli (EHEC) and associated with life-threatening illnesses. Cattle and beef are considered typical sources of STEC, but their presence in pork products is a growing concern. Therefore, carcasses ( n  = 1,536) at two U.S. pork processors were sampled once per season at three stages of harvest (poststunning skins, postscald carcasses, and chilled carcasses) and then examined using PCR for Shiga toxin genes ( stx ), intimin genes ( eae ), aerobic plate count (APC), and Enterobacteriaceae counts (EBC). The prevalence of stx on skins, postscald, and chilled carcasses was 85.3, 17.5, and 5.4%, respectively, with 82.3, 7.8, and 1.7% of swabs, respectively, having stx and eae present. All stx -positive samples were subjected to culture isolation that resulted in 368 STEC and 46 EHEC isolates. The most frequently identified STEC were serogroups O121, O8, and O91 (63, 6.7, and 6.0% of total STEC, respectively). The most frequently isolated EHEC was serotype O157:H7 (63% of total EHEC). Results showed that scalding significantly reduced ( P <  0.05) carcass APC and EBC by 3.00- and 2.50-log 10 CFU/100 cm 2 , respectively. A seasonal effect was observed, with STEC prevalence lower ( P  < 0.05) in winter. The data from this study show significant ( P  < 0.05) reduction in the incidence of STEC ( stx ) from 85.3% to 5.4% and of EHEC ( stx plus eae ) from 82.3% to 1.7% within the slaughter-to-chilling continuum, respectively, and that potential EHEC can be confirmed present throughout using culture isolation. IMPORTANCE Seven serogroups of STEC are responsible for most (>75%) cases of severe illnesses caused by STEC and are considered adulterants of beef. However, some STEC outbreaks have been attributed to pork products, although the same E. coli are not considered adulterants in pork because little is known of their prevalence along the pork chain. The significance of the work presented here is that it identifies disease-causing STEC, EHEC, demonstrating that these same organisms are a food safety hazard in pork as well as beef. The results show that most STEC isolated from pork are not likely to cause severe disease in humans and that processes used in pork harvest, such as scalding, offer a significant control point to reduce contamination. The results will assist the pork processing industry and regulatory agencies to optimize interventions to improve the safety of pork products., (Copyright © 2020 American Society for Microbiology.)

The objectives of this study were (1) to estimate the prevalence and concentration of the seven major Shiga toxin-producing Escherichia coli (STEC) serogroups (O26, O45, O103, O111, O121, O145, and O157), collectively called STEC-7, on cattle hides collected in different seasons and beef processing plants; and (2) to determine associations of season, plant, and hide cleanliness scores with the prevalence and concentration of STEC-7. A total of 720 hide surface samples (240/season) were collected over three seasons (summer and fall 2015 and spring 2016) from beef cattle carcasses in four commercial processing plants in the United States. Samples were subjected to selective culture and spiral plating methods. Overall model-adjusted mean prevalence (95% confidence interval) was 0.3% (0.03-2.3%) for STEC O26; 0.05% (<0.01-8.5%) for STEC O45; 0.2% (0.02-1.9%) for STEC O103; 0.05% (<0.01-8.5%) for STEC O145; and 3.1% (0.6-15.2%) for STEC O157. Four percent of hide samples were enumerable for STEC O157; mean concentration (standard deviation) = 2.1 (0.7) log 10 colony-forming units (CFUs)/100 cm 2 . No samples were enumerable for non-O157 STEC. Hide-on prevalence of STEC O157 and STEC non-O157 (specifically of STEC O103) was higher in summer and spring, respectively. Across seasons and plants, the most common STEC non-O157 serogroups in this study (O26 and O103) were associated with a higher prevalence of STEC O157. Season and plant played a role in prevalence and concentration of STEC in beef cattle hides, varying by serogroup. Tailoring mitigation strategies at the plant can be challenging and processors would benefit from supplementary preharvest interventions to reduce overall contamination pressure at the plant, especially in fall and spring months when hide-on prevalence of STEC non-O157 is higher.

The U.S. Food and Drug Administration Escherichia coli Identification (FDA-ECID) microarray provides rapid molecular characterization of E. coli. The effectiveness of the FDA-ECID for characterizing Shiga toxin-producing E. coli (STEC) was evaluated by three federal laboratories and one reference laboratory with a panel of 54 reference E. coli strains from the External Quality Assurance program. Strains were tested by FDA-ECID for molecular serotyping (O and H antigens), Shiga toxin subtyping, and the presence of the ehxA and eae genes for enterohemolysin and intimin, respectively. The FDA-ECID O typing was 96% reproducible among the four laboratories and 94% accurate compared with the reference External Quality Assurance data. Discrepancies were due to the absence of O41 target loci on the array and to two pairs of O types with identical target sequences. H typing was 96% reproducible and 100% accurate, with discrepancies due to two strains from one laboratory that were identified as mixed by FDA-ECID. Shiga toxin (Stx) type 1 subtyping was 100% reproducible and accurate, and Stx2 subtyping was 100% reproducible but only 64% accurate. FDA-ECID identified most Stx2 subtypes but had difficulty distinguishing among stx 2a , stx 2c , and stx 2d genes because of close similarities of these sequences. FDA-ECID was 100% effective for detecting ehxA and eae and accurately subtyped the eae alleles. This interlaboratory study revealed that FDA-ECID for STEC characterization was highly reproducible for molecular serotyping, stx and eae subtyping, and ehxA detection. However, the array was less useful for distinguishing among the highly homologous O antigen genes and the stx 2a , stx 2c , and stx 2d subtypes.

The objective of this research was to assess the microbiological status of leafy greens, sprouts, and melons from U.S. markets. A total of 14,183 samples of leafy greens, 2,652 samples of sprouts, and 3,411 samples of melons were collected throughout the United States from 2009 to 2014. The samples were analyzed for aerobic plate counts, total coliform counts, Escherichia coli counts, and the presence and levels of Salmonella, Shigella, Listeria monocytogenes, and Shiga toxin-producing E. coli (STEC), depending on the year and type of produce. Among the leafy greens, no E. coli O157:H7 or non-O157 STEC were detected from iceberg lettuce samples. The overall prevalences of Salmonella, E. coli O157:H7, non-O157 STEC, and L. monocytogenes in the 14,183 samples of leafy greens were 0.05, 0.01, 0.07, and 0.11%, respectively. Among sprout samples, no Salmonella or E. coli O157:H7 was detected, and the overall prevalences of non-O157 STEC and L. monocytogenes were 0.04 and 0.11%, respectively. Among melon samples, no Salmonella was detected from cucumbers, no L. monocytogenes was detected from cantaloupes, and the overall prevalences of Salmonella and L. monocytogenes were 0.12 and 0.23%, respectively. L. monocytogenes levels were 0.4 to 1,470 most probable number (MPN)/g in leafy greens, 0.36 to 1,100 MPN/g in sprouts, and <0.03 to 150 MPN/g in melons, and most positive samples had low levels of these pathogens. The isolates from these foods were very diverse genetically. Foodborne pathogens, including Salmonella, STEC, and L. monocytogenes, had relatively low prevalences in the produce surveyed. Because these foods are usually consumed raw, measures should be taken to significantly minimize the presence and levels of human pathogens.

Shiga toxin-producing Escherichia coli (STEC) is among the common causes of foodborne gastroenteritis. STEC is defined by the production of specific toxins, but within this pathotype there is a diverse group of organisms. This diversity has important consequences for understanding the pathogenesis of the organism, as well as for selecting the optimum strategy for diagnostic testing in the clinical laboratory. This review includes discussions of the mechanisms of pathogenesis, the range of manifestations of infection, and the several different methods of laboratory detection of Shiga toxin-producing E coli., (Copyright © 2015 Elsevier Inc. All rights reserved.)

We describe multiple-aetiology infections involving non-O157 Shiga toxin-producing Escherichia coli (STEC) identified through laboratory-based surveillance in nine FoodNet sites from 2001 to 2010. A multiple-aetiology infection (MEI) was defined as isolation of non-O157 STEC and laboratory evidence of any of the other nine pathogens under surveillance or isolation of >1 non-O157 STEC serogroup from the same person within a 7-day period. We compared exposures of patients with MEI during 2001-2010 with those of patients with single-aetiology non-O157 STEC infections (SEI) during 2008-2009 and with those of the FoodNet population from a survey conducted during 2006-2007. In total, 1870 non-O157 STEC infections were reported; 68 (3.6%) were MEI; 60 included pathogens other than non-O157 STEC; and eight involved >1 serogroup of non-O157 STEC. Of the 68 MEI, 21 (31%) were part of six outbreaks. STEC O111 was isolated in 44% of all MEI. Of patients with MEI, 50% had contact with farm animals compared with 29% (P < 0.01) of persons with SEI; this difference was driven by infections involving STEC O111. More patients with non-outbreak-associated MEI reported drinking well water (62%) than respondents in a population survey (19%) (P < 0.01). Drinking well water and having contact with animals may be important exposures for MEI, especially those involving STEC O111., (© 2014 Blackwell Verlag GmbH.)

Each year, >9 million foodborne illnesses are estimated to be caused by major pathogens acquired in the United States. Preventing these illnesses is challenging because resources are limited and linking individual illnesses to a particular food is rarely possible except during an outbreak. We developed a method of attributing illnesses to food commodities that uses data from outbreaks associated with both simple and complex foods. Using data from outbreak-associated illnesses for 1998-2008, we estimated annual US foodborne illnesses, hospitalizations, and deaths attributable to each of 17 food commodities. We attributed 46% of illnesses to produce and found that more deaths were attributed to poultry than to any other commodity. To the extent that these estimates reflect the commodities causing all foodborne illness, they indicate that efforts are particularly needed to prevent contamination of produce and poultry. Methods to incorporate data from other sources are needed to improve attribution estimates for some commodities and agents.