Outbreak of multiple strains of non-O157 Shiga toxin-producing and enteropathogenic Escherichia coli associated with rocket salad, Finland, autumn 2016

Assessment of the presence of Acinetobacter spp. resistant to β-lactams in commercial ready-to-eat salad samples

Acinetobacter baumannii is a well-known nosocomial infection causing agent. However, other Acinetobacter spp. have also been implicated in cases of human infection. Additionally, these bacteria are known for the development of antibiotic resistance thus making the treatment of the infections they cause, challenging. Due to their relevance in clinical setups less attention has been paid to their presence in foods, and its relation with infection/dissemination routes. In the current study commercial Ready-To-Eat (RTE) salads were analyzed seeking for antibiotic resistant Acinetobacter spp. A preliminary screening allowed us to recover Gram-negative bacteria resistant to β - lactams using cefotaxime, third generation cephalosporins, as the selective agent, and this was followed by identification with CHROMagar™ Acinetobacter and 16S rDNA sequencing. Finally, the isolates identified as Acinetobacter spp. were reanalyzed by PCR to determine the presence of nine potential Extended Spectrum β Lactamases (ESBL). Two commercial RTE salad brands were included in the study (2 batches per brand and 8 samples of each batch making a total of 32 independent samples), and compared against an organic lettuce. High concentrations of β - lactam, resistant bacteria were found in all the samples tested (5 log CFU/g). Additionally, 209 isolates were phenotypically characterized on CHROMagar Acinetobacter. Finally, PCR analysis identified the presence of different ESBL genes, being positive for blaACC, blaSHV, blaDHA and blaVEB; out of these, blaACC was the most prevalent. None of the isolates screened were positive for more than one gene. To conclude, it is important to highlight the fact that pathogenic species within the genus Acinetobacter spp., other than A. baumannii, have been identified bearing resistance genes not typically associated to these microorganisms highlight the importance of continuous surveillance.

Strain-level characterization of foodborne pathogens without culture enrichment for outbreak investigation using shotgun metagenomics facilitated with nanopore adaptive sampling

Introduction

Shotgun metagenomics has previously proven effective in the investigation of foodborne outbreaks by providing rapid and comprehensive insights into the microbial contaminant. However, culture enrichment of the sample has remained a prerequisite, despite the potential impact on pathogen detection resulting from the growth competition. To circumvent the need for culture enrichment, we explored the use of adaptive sampling using various databases for a targeted nanopore sequencing, compared to shotgun metagenomics alone.

Methods

The adaptive sampling method was first tested on DNA of mashed potatoes mixed with DNA of a Staphylococcus aureus strain previously associated with a foodborne outbreak. The selective sequencing was used to either deplete the potato sequencing reads or enrich for the pathogen sequencing reads, and compared to a shotgun sequencing. Then, living S. aureus were spiked at 105 CFU into 25 g of mashed potatoes. Three DNA extraction kits were tested, in combination with enrichment using adaptive sampling, following whole genome amplification. After data analysis, the possibility to characterize the contaminant with the different sequencing and extraction methods, without culture enrichment, was assessed.

Results

Overall, the adaptive sampling outperformed the shotgun sequencing. While the use of a host removal DNA extraction kit and targeted sequencing using a database of foodborne pathogens allowed rapid detection of the pathogen, the most complete characterization was achieved when using solely a database of S. aureus combined with a conventional DNA extraction kit, enabling accurate placement of the strain on a phylogenetic tree alongside outbreak cases.

Discussion

This method shows great potential for strain-level analysis of foodborne outbreaks without the need for culture enrichment, thereby enabling faster investigations and facilitating precise pathogen characterization. The integration of adaptive sampling with metagenomics presents a valuable strategy for more efficient and targeted analysis of microbial communities in foodborne outbreaks, contributing to improved food safety and public health.

Genetic Characterization of Intimin Gene (eae) in Clinical Shiga Toxin-Producing Escherichia coli Strains from Pediatric Patients in Finland

Shiga toxin (Stx)-producing Escherichia coli (STEC) infections cause outbreaks of severe disease in children ranging from bloody diarrhea to hemolytic uremic syndrome (HUS). The adherent factor intimin, encoded by eae, can facilitate the colonization process of strains and is frequently associated with severe disease. The purpose of this study was to examine and analyze the prevalence and polymorphisms of eae in clinical STEC strains from pediatric patients under 17 years old with and without HUS, and to assess the pathogenic risk of different eae subtypes. We studied 240 STEC strains isolated from pediatric patients in Finland with whole genome sequencing. The gene eae was present in 209 (87.1%) strains, among which 49 (23.4%) were from patients with HUS, and 160 (76.6%) were from patients without HUS. O157:H7 (126, 60.3%) was the most predominant serotype among eae-positive STEC strains. Twenty-three different eae genotypes were identified, which were categorized into five eae subtypes, i.e., γ1, β3, ε1, θ and ζ3. The subtype eae-γ1 was significantly overrepresented in strains from patients aged 5-17 years, while β3 and ε1 were more commonly found in strains from patients under 5 years. All O157:H7 strains carried eae-γ1; among non-O157 strains, strains of each serotype harbored one eae subtype. No association was observed between the presence of eae/its subtypes and HUS. However, the combination of eae-γ1+stx2a was significantly associated with HUS. In conclusion, this study demonstrated a high occurrence and genetic variety of eae in clinical STEC from pediatric patients under 17 years old in Finland, and that eae is not essential for STEC-associated HUS. However, the combination of certain eae subtypes with stx subtypes, i.e., eae-γ1+stx2a, may be used as risk predictors for the development of severe disease in children.

A worldwide review of illness outbreaks involving mixed salads/dressings and factors influencing product safety and shelf life

The trends toward healthy living, vegetarianism, and busy schedules have increased salad popularity. Salads are usually consumed raw without any thermal treatment, and therefore, without proper care they can become major vehicles for foodborne illness outbreaks. This review examines the microbial quality of 'dressed' salads which contain two or more vegetables/fruits and salad dressings. The possible sources of ingredient contamination, recorded illnesses/outbreaks, and overall microbial quality observed worldwide, besides the antimicrobial treatments available are discussed in detail. Noroviruses were most frequently implicated in outbreaks. Salad dressings usually play a positive role in influencing microbial quality. However, this depends on several factors like the type of contaminating microorganism, storage temperature, dressing pH and ingredients, plus the type of salad vegetable. Very limited literature exists on antimicrobial treatments that can be used successfully with salad dressings and 'dressed' salads. The challenge with antimicrobial treatments is to find ones sufficiently broad in spectrum, compatible with produce flavour which can be applied at competitive cost. It is evident that renewed emphasis on prevention of produce contamination at the producer, processor, wholesale and retail levels plus enhanced hygiene vigilance at foodservice will have a major impact on reducing the risk of foodborne illnesses from salads.

Pathophysiology of enteropathogenic Escherichia coli during a host infection

Enteropathogenic Escherichia coli (EPEC) is a major cause of infantile diarrhea in developing countries. However, sporadic outbreaks caused by this microorganism in developed countries are frequently reported recently. As an important zoonotic pathogen, EPEC is being monitored annually in several countries. Hallmark of EPEC infection is formation of attaching and effacing (A/E) lesions on the small intestine. To establish A/E lesions during a gastrointestinal tract (GIT) infeciton, EPEC must thrive in diverse GIT environments. A variety of stress responses by EPEC have been reported. These responses play significant roles in helping E. coli pass through GIT environments and establishing E. coli infection. Stringent response is one of those responses. It is mediated by guanosine tetraphosphate. Interestingly, previous studies have demonstrated that stringent response is a universal virulence regulatory mechanism present in many bacterial pathogens including EPEC. However, biological signficance of a bacterial stringent response in both EPEC and its interaction with the host during a GIT infection is unclear. It needs to be elucidated to broaden our insight to EPEC pathogenesis. In this review, diverse responses, including stringent response, of EPEC during a GIT infection are discussed to provide a new insight into EPEC pathophysiology in the GIT.

Anti-listerial properties of chemical constituents of Eruca sativa (rocket salad): From industrial observation to in vitro activity

The frequency of foodborne outbreaks epidemiologically associated with Listeria monocytogenes in fresh produce has increased in recent years. Although L. monocytogenes may be transferred from the environment to vegetables during farming, contamination of food products most commonly occurs in food processing facilities, where L. monocytogenes has the ability to establish and persist on processing equipment. The current study was undertaken to collect data on the occurrence of L. monocytogenes and the identity of the endogenous microbiota in a fresh produce processing facility, for which information has remained scarce. L. monocytogenes was not detected in the facility. Experiments simulating conditions in the processing environment were performed, including examination of bacterial growth in nutrients based on vegetables (salad juice) compared to in other types of nutrients (fish, meat). Results showed that the endogenous microbiota (dominated by Pseudomonas) grew well in iceberg lettuce and rocket salad juice at low temperatures, while growth inhibition of L. monocytogenes was observed, particularly in rocket salad juice. The anti-listerial activity in rocket salad juice was retained in a polar chromatographic fraction containing several metabolites. Characterization of this active fraction, using LC-MS/MS, led to identification of 19 compounds including nucleosides and amino acids. Further work is necessary to determine the molecular mechanism responsible for the inhibitory activity of rocket salad constituents. The study nevertheless suggests that the available nutrients, as well as a low temperature (3 °C) and the in-house bacterial flora, may influence the prevalence of L. monocytogenes in fresh produce processing facilities.

Antimicrobial Resistance of Non-O157 Shiga Toxin-Producing Escherichia coli Isolated from Humans and Domestic Animals

Non-O157 Shiga toxin-producing Escherichia coli (STEC) is an important pathogen that can cause zoonotic diseases. To investigate the antimicrobial resistance of STEC in China, non-O157 STEC isolates, recovered from domestic animals and humans from 12 provinces, were analyzed using antimicrobial susceptibility testing and whole genome characterization. Out of the 298 isolates tested, 115 strains showed resistance to at least one antimicrobial and 85 strains showed multidrug resistance. The highest resistance rate was to tetracycline (32.6%), followed by nalidixic acid (25.2%) and chloramphenicol and azithromycin (both 18.8%). However, imipenem and meropenem were effective against all isolates. Antimicrobial resistance patterns varied among strains from different sources. Strains from pig, sheep, humans, and cattle showed resistance rates of 100.0%, 46.9%, 30.3%, and 6.3% to one or more antimicrobials, respectively. Forty-three genes related to 11 antimicrobial classes were identified among these strains. The colistin-resistance gene mcr was only carried by strains from pigs. A new fosfomycin-resistant gene, fosA7, was detected in strains from humans, cattle, and sheep. Whole genome phylogenetic analysis showed that strains from the four sources were genetically diverse and scattered throughout the phylogenetic tree; however, some strains from the same source had a tendency to cluster closely. These results provide a reference to monitor the emergence and spread of multidrug resistant STEC strains among animals and humans. Furthermore, with a better understanding of antimicrobial genotypes and phenotypes among the diverse STEC strains obtained, this study could guide the administration of antimicrobial drugs in STEC infections when necessary.

Do changes in STEC diagnostics mislead interpretation of disease surveillance data in Switzerland? Time trends in positivity, 2007 to 2016

BackgroundLaboratory-confirmed cases of Shiga toxin-producing Escherichia coli (STEC) have been notifiable to the National Notification System for Infectious Diseases in Switzerland since 1999. Since 2015, a large increase in case numbers has been observed. Around the same time, syndromic multiplex PCR started to replace other diagnostic methods in standard laboratory practice for gastrointestinal pathogen testing, suggesting that the increase in notified cases is due to a change in test practices and numbers.AimThis study examined the impact of changes in diagnostic methods, in particular the introduction of multiplex PCR panels, on routine STEC surveillance data in Switzerland.MethodsWe analysed routine laboratory data from 11 laboratories, which reported 61.9% of all STEC cases from 2007 to 2016 to calculate the positivity, i.e. the rate of the number of positive STEC tests divided by the total number of tests performed.ResultsThe introduction of multiplex PCR had a strong impact on STEC test frequency and identified cases, with the number of tests performed increasing sevenfold from 2007 to 2016. Still, age- and sex-standardised positivity increased from 0.8% in 2007 to 1.7% in 2016.ConclusionIncreasing positivity suggests that the increase in case notifications cannot be attributed to an increase in test numbers alone. Therefore, we cannot exclude a real epidemiological trend for the observed increase. Modernising the notification system to address current gaps in information availability, e.g. diagnostic methods, and improved triangulation of clinical presentation, diagnostic and serotype information are needed to deal with emerging disease and technological advances.

The use of multiple hypothesis-generating methods in an outbreak investigation of Escherichia coli O121 infections associated with wheat flour, Canada 2016-2017

A Canadian outbreak investigation into a cluster of Escherichia coli O121 was initiated in late 2016. When initial interviews using a closed-ended hypothesis-generating questionnaire did not point to a common source, cases were centrally re-interviewed using an open-ended approach. The open-ended interviews led cases to describe exposures with greater specificity, as well as food preparation activities. Data collected supported hypothesis generation, particularly with respect to flour exposures. In March 2017, an open sample of Brand X flour from a case home, and a closed sample collected at retail of the same brand and production date, tested positive for the outbreak strain of E. coli O121. In total, 76% (16/21) of cases reported that they used or probably used Brand X flour or that it was used or probably was used in the home during their exposure period. Crucial hypothesis-generating techniques used during the course of the investigation included a centralised open-ended interviewing approach and product sampling from case homes. This was the first outbreak investigation in Canada to identify flour as the source of infection.

A practical composite risk score for the development of Haemolytic Uraemic Syndrome from Shiga toxin-producing Escherichia coli

BACKGROUND

Haemolytic Uraemic Syndrome (HUS) is a serious complication of Shiga toxin-producing Escherichia coli (STEC) infection and the key reason why intensive health protection against STEC is required. However, although many potential risk factors have been identified, accurate estimation of risk of HUS from STEC remains challenging. Therefore, we aimed to develop a practical composite score to promptly estimate the risk of developing HUS from STEC.

METHODS

This was a retrospective cohort study where data for all confirmed STEC infections in Ireland during 2013-15 were subjected to statistical analysis with respect to predicting HUS. Multivariable logistic regression was used to develop a composite risk score, segregating risk of HUS into 'very low risk' (0-0.4%), 'low risk' (0.5-0.9%), 'medium risk' (1.0-4.4%), 'high risk' (4.5-9.9%) and 'very high risk' (10.0% and over).

RESULTS

There were 1397 STEC notifications with complete information regarding HUS, of whom 5.1% developed HUS. Young age, vomiting, bloody diarrhoea, Shiga toxin 2, infection during April to November, and infection in Eastern and North-Eastern regions of Ireland, were all statistically significant independent predictors of HUS. Demonstration of a risk gradient provided internal validity to the risk score: 0.2% in the cohort with 'very low risk' (1/430), 1.1% with 'low risk' (2/182), 2.3% with 'medium risk' (8/345), 3.1% with 'high risk' (3/98) and 22.2% with 'very high risk' (43/194) scores, respectively, developed HUS.

CONCLUSION

We have developed a composite risk score which may be of practical value, once externally validated, in prompt estimation of risk of HUS from STEC infection.

Enteroaggregative E. coli Adherence to Human Heparan Sulfate Proteoglycans Drives Segment and Host Specific Responses to Infection

Enteroaggregative Escherichia coli (EAEC) is a significant cause of acute and chronic diarrhea, foodborne outbreaks, infections of the immunocompromised, and growth stunting in children in developing nations. There is no vaccine and resistance to antibiotics is rising. Unlike related E. coli pathotypes that are often associated with acute bouts of infection, EAEC is associated with persistent diarrhea and subclinical long-term colonization. Several secreted virulence factors have been associated with EAEC pathogenesis and linked to disease in humans, less certain are the molecular drivers of adherence to the intestinal mucosa. We previously established human intestinal enteroids (HIEs) as a model system to study host-EAEC interactions and aggregative adherence fimbriae A (AafA) as a major driver of EAEC adherence to HIEs. Here, we report a large-scale assessment of the host response to EAEC adherence from all four segments of the intestine across at least three donor lines for five E. coli pathotypes. The data demonstrate that the host response in the duodenum is driven largely by the infecting pathotype, whereas the response in the colon diverges in a patient-specific manner. Major pathways altered in gene expression in each of the four enteroid segments differed dramatically, with responses observed for inflammation, apoptosis and an overwhelming response to different mucin genes. In particular, EAEC both associated with large mucus droplets and specific mucins at the epithelial surface, binding that was ameliorated when mucins were removed, a process dependent on AafA. Pan-screening for glycans for binding to purified AafA identified the human ligand as heparan sulfate proteoglycans (HSPGs). Removal of HSPG abrogated EAEC association with HIEs. These results may mean that the human intestine responds remarkably different to distinct pathobionts that is dependent on the both the individual and intestinal segment in question, and uncover a major role for surface heparan sulfate proteoglycans as tropism-driving factor in adherence and/or colonization.

A Practical Method to Implement Strain-Level Metagenomics-Based Foodborne Outbreak Investigation and Source Tracking in Routine

The management of a foodborne outbreak depends on the rapid and accurate identification of the responsible food source. Conventional methods based on isolation of the pathogen from the food matrix and target-specific real-time polymerase chain reactions (qPCRs) are used in routine. In recent years, the use of whole genome sequencing (WGS) of bacterial isolates has proven its value to collect relevant information for strain characterization as well as tracing the origin of the contamination by linking the food isolate with the patient's isolate with high resolution. However, the isolation of a bacterial pathogen from food matrices is often time-consuming and not always successful. Therefore, we aimed to improve outbreak investigation by developing a method that can be implemented in reference laboratories to characterize the pathogen in the food vehicle without its prior isolation and link it back to human cases. We tested and validated a shotgun metagenomics approach by spiking food pathogens in specific food matrices using the Shiga toxin-producing Escherichia coli (STEC) as a case study. Different DNA extraction kits and enrichment procedures were investigated to obtain the most practical workflow. We demonstrated the feasibility of shotgun metagenomics to obtain the same information as in ISO/TS 13136:2012 and WGS of the isolate in parallel by inferring the genome of the contaminant and characterizing it in a shorter timeframe. This was achieved in food samples containing different E. coli strains, including a combination of different STEC strains. For the first time, we also managed to link individual strains from a food product to isolates from human cases, demonstrating the power of shotgun metagenomics for rapid outbreak investigation and source tracking.

Interactions of Shiga toxin-producing Escherichia coli with leafy green vegetables

Shiga toxin-producing Escherichia coli (STEC) are important foodborne pathogens responsible for a wide spectrum of diseases including diarrhea, bloody diarrhea, and hemolytic uremic syndrome (HUS). A considerable number of outbreaks and sporadic cases of HUS have been associated with ingestion of fresh ready-to-eat products. Maintenance and persistence of STEC in the environment and foods can be related to its ability to form biofilm. A non-O157 STEC strain isolated from bovine feces was distinguished by its great ability to form biofilm in abiotic surfaces. In the present study, we aimed to investigate the ability of this strain to adhere to rocket leaves (Eruca sativa). Adherence assays were carried out for 3 h at 28 °C and analyzed by scanning electron microscopy. The non-O157 STEC strain adhered to leaf surface and inside the stomata forming several bacterial aggregates. The number of adherent bacteria per square millimeter of leaf was eightfold higher compared with an O157 STEC strain. Deletion of the STEC autotransporter protein contributing to biofilm (Sab) reduced the adherence ability of the non-O157 strain in almost 50%, and deletion of antigen 43 (Ag43) almost abolished this interaction. Very few bacteria were seen on the leaf surface, and these differences were statistically significant, suggesting the role of both proteins and especially Ag43 in the interaction of the non-O157 STEC strain with leaves. The risk posed by non-O157 STEC adherence to leaves on fresh produce contamination should not be neglected, and measures that effectively control adherence should be included in strategies to control non-O157 STEC.

Biofilm formation by South African non-O157 Shiga toxigenic Escherichia coli on stainless steel coupons

This study examined the biofilm-forming ability of six non-O157 Shiga-toxin-producing Escherichia coli (STEC) strains: O116:H21, wzx-Onovel5:H19, O129:H21, O129:H23, O26:H11, and O154:H10 on stainless steel coupons after 24, 48, and 72 h of incubation at 22 °C and after 168 h at 10 °C. The results of crystal violet staining revealed that strains O129:H23 and O154:H10 were able to form biofilms on both the submerged surface and the air-liquid interface of coupons, whereas strains O116:H21, wzx-Onovel5:H19, O129:H21, and O26:H11 formed biofilm only at the air-liquid interface. Viable cell counts and scanning electron microscopy showed that biofilm formation increased (p < 0.05) over time. The biofilm-forming ability of non-O157 STEC was strongest (p < 0.05) at 22 °C after 48 h of incubation. The strongest biofilm former regardless of temperature was O129:H23. Generally, at 10 °C, weak to no biofilm was observed for isolates O154:H10, O116:H21, wzx-Onovel5:H19, O26:H11, and O129:H21 after 168 h. This study found that temperature affected the biofilm-forming ability of non-O157 STEC strains. Overall, our data indicate a high potential for biofilm formation by the isolates at 22 °C, suggesting that non-O157 STEC strains could colonize stainless steel within food-processing facilities. This could serve as a potential source of adulteration and promote the dissemination of these potential pathogens in food.

Hemolytic uremic syndrome caused by Shiga toxin-producing Escherichia coli in children: incidence, risk factors, and clinical outcome

BACKGROUND

Hemolytic uremic syndrome (HUS) is a multisystemic disease. In a nationwide study, we characterized the incidence, clinical course, and prognosis of HUS caused by Shiga toxin (Stx)-producing Escherichia coli (STEC) strains with emphasis on risk factors, disease severity, and long-term outcome.

METHODS

The data on pediatric HUS patients from 2000 to 2016 were collected from the medical records. STEC isolates from fecal cultures of HUS and non-HUS patients were collected from the same time period and characterized by whole genome sequencing analysis.

RESULTS

Fifty-eight out of 262 culture-positive cases developed verified (n = 58, 22%) STEC-HUS. Another 29 cases had probable STEC-HUS, the annual incidence of STEC-HUS being 0.5 per 100,000 children. Eleven different serogroups were detected, O157 being the most common (n = 37, 66%). Age under 3 years (OR 2.4), stx2 (OR 9.7), and stx2a (OR 16.6) were found to be risk factors for HUS. Fifty-five patients (63%) needed dialysis. Twenty-nine patients (33%) developed major neurological symptoms. Complete renal recovery was observed in 57 patients after a median 4.0 years of follow-up. Age under 3 years, leukocyte count over 20 × 10⁹/L, and need for dialysis were predictive factors for poor renal outcome.

CONCLUSIONS

Age under 3 years, stx2, and stx2a were risk factors for HUS in STEC-positive children. However, serogroup or stx types did not predict the renal outcome or major CNS symptoms.

Whole genome sequencing and metagenomics for outbreak investigation, source attribution and risk assessment of food-borne microorganisms

This Opinion considers the application of whole genome sequencing (WGS) and metagenomics for outbreak investigation, source attribution and risk assessment of food‐borne pathogens. WGS offers the highest level of bacterial strain discrimination for food‐borne outbreak investigation and source‐attribution as well as potential for more precise hazard identification, thereby facilitating more targeted risk assessment and risk management. WGS improves linking of sporadic cases associated with different food products and geographical regions to a point source outbreak and can facilitate epidemiological investigations, allowing also the use of previously sequenced genomes. Source attribution may be favoured by improved identification of transmission pathways, through the integration of spatial‐temporal factors and the detection of multidirectional transmission and pathogen–host interactions. Metagenomics has potential, especially in relation to the detection and characterisation of non‐culturable, difficult‐to‐culture or slow‐growing microorganisms, for tracking of hazard‐related genetic determinants and the dynamic evaluation of the composition and functionality of complex microbial communities. A SWOT analysis is provided on the use of WGS and metagenomics for Salmonella and Shigatoxin‐producing Escherichia coli (STEC) serotyping and the identification of antimicrobial resistance determinants in bacteria. Close agreement between phenotypic and WGS‐based genotyping data has been observed. WGS provides additional information on the nature and localisation of antimicrobial resistance determinants and on their dissemination potential by horizontal gene transfer, as well as on genes relating to virulence and biological fitness. Interoperable data will play a major role in the future use of WGS and metagenomic data. Capacity building based on harmonised, quality controlled operational systems within European laboratories and worldwide is essential for the investigation of cross‐border outbreaks and for the development of international standardised risk assessments of food‐borne microorganisms.

Did the ban on serving raw beef liver in restaurants decrease Enterohemorrhagic Escherichia coli infection in Japan?: an interrupted time-series analysis

Background

Enterohemorrhagic Escherichia coli (EHEC) is an important pathogen that causes diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS). After an EHEC outbreak involving uncooked beef, serving raw beef liver dishes at restaurants was completely banned starting on July 1, 2012 in Japan. However, its long-term associations with the incidence rates of EHEC infections have never been assessed by formal interrupted time-series analysis (ITSA).

Methods

A retrospective cohort study to assess the impact of banning raw beef liver provision at restaurants was conducted. The weekly incidence of asymptomatic and symptomatic EHEC infections, the incidence of HUS, and deaths were extracted from the national reportable diseases database from January 2008 to December 2017. ITSA was conducted to evaluate the impact of banning raw beef liver from July 2012. To account for a potential simultaneous external effect, the additional regulation on raw beef red meat handling (implemented in May 2011) and the seasonality were also incorporated into the model.

Results

There were 32,179 asymptomatic and 21,250 symptomatic EHEC infections (including 717 HUS cases and 26 deaths) reported during the study period. During the pre-intervention period (before week 27, 2012), there were 0.45 asymptomatic EHEC infections per million-persons per week. The mean post-intervention asymptomatic EHEC infections were 0.51 per million-persons per week. ITSA revealed no baseline trend or change in the intercept and trend (0.002 infections per million-persons per week, 95% Confidence interval − 0.03-0.04, p = 0.93, 1.22, CI -1.96-4.39, p = 0.45, and − 0.006, CI -0.003-0.02, p = 0.68, respectively). For symptomatic EHEC infections, there were 0.30 cases per million per week during the pre-intervention period, and it became 0.33 cases per million per week after the intervention. Time series modeling again did not show a significant baseline trend or changes in the intercept and trend (0.0005, CI -0.02-0.02, p = 0.96, 0.69, CI -1.75-3.12, p = 0.58, and − 0.003, CI -0.02-0.01, p = 0.76, respectively).

Conclusion

We did not find a statistically significant reduction in the overall incidence rates of both asymptomatic and symptomatic EHEC infections in Japan after implementing measures, including a ban on serving raw beef liver dishes in the restaurant industry.

Outbreaks of Shiga Toxin-Producing Escherichia coli Linked to Sprouted Seeds, Salad, and Leafy Greens: A Systematic Review

Shiga toxin-producing Escherichia coli (STEC) outbreaks involving ready-to-eat salad products have been described in the scientific literature since 1995. These products typically do not undergo a definitive control step such as cooking to eliminate pathogens. To reduce the number of STEC infections from salad products, efforts will need to focus on preventing and reducing contamination throughout the food chain. We performed a systematic review of STEC outbreaks involving sprouted seeds, salad, or leafy green products to determine whether there were recurrent features, such as availability of microbiological evidence or identification of the contamination event, which may inform future investigations and prevention and control strategies. Thirty-five STEC outbreaks linked to contaminated leafy greens were identified for inclusion. The outbreaks occurred from 1995 to 2018 and ranged from 8 to more than 8,500 cases. Detection of STEC in the food product was rare (4 of 35 outbreaks). For the remaining outbreaks, the determination of leafy greens as the source of the outbreak mainly relied on analytical epidemiology (20 of 35) or descriptive evidence (11 of 35). The traceback investigation in 21 of 32 outbreaks was not able to identify possible routes leading to where the STEC bacteria came from or how the leaves were contaminated. Investigations in eight outbreaks found poor practice during processing that may have contributed to the outbreak, such as insufficient postharvest disinfection of the product. Six outbreak investigations were able to identify the outbreak strain in animal feces near the growing fields; two of these were also able to find it in irrigation water on the farms, providing a likely route of contamination. These results highlight the limitations of relying on microbiological confirmation as a basis to initiate investigations of upstream production to understand the source of contamination. This review also demonstrates the importance of, and difficulties associated with, food-chain traceback studies to inform control measures and future prevention.