Attributing sporadic and outbreak-associated infections to sources: blending epidemiological data

Determinants of Sporadic Shiga Toxin-Producing Escherichia coli (STEC) Infection in Denmark, 2018-2020: A Matched Case-Control Study

Infections with Shiga toxin-producing Escherichia coli (STEC) are increasing in Denmark and elsewhere. STEC is also the most frequent cause of haemolytic uraemic syndrome (HUS) in Danish children. Most cases are considered sporadic, while approximately one-third can be attributed to a known source of infection. Hence, we examined sources of sporadic STEC infection in Denmark. From January 2018 to December 2020, we conducted a prospective nationwide case-control study among Danish adults and children. Cases with confirmed positive STEC infection were notified infections within the national laboratory surveillance system. Control persons were randomly selected from the Danish Civil Registration System, individually matched in age in 5-year bands and sex. Participants were invited by an electronic letter to complete either an adult or child questionnaire online. Univariate and adjusted matched odds ratios were computed for adults and children using conditional logistic regression. The study recruited 1583 STEC cases and 6228 controls. A total of 658 cases (42%) and 2155 controls (35%) were included in the analysis. Depending on age, univariate analysis adjusted for socio-demographic determinants showed that the consumption of boiled beef (mOR = 2.2, 95% confidence interval (CI): 1.6-3.1) and fried minced beef (mOR = 1.6, CI: 1.2-2.1), drinking raw (unpasteurized) milk (mOR = 11, CI 1.1-110), eating grilled food (mOR = 9.8, CI: 5.6-17) and having a household member using diapers (mOR = 2.1, CI: 1.4-3.2) were determinants of sporadic STEC infection. Further multivariate adjusted analysis resulted in the same determinants. This study confirms that beef is an overall important risk factor for STEC infection in Denmark. We also present evidence that a proportion of sporadic STEC infections in Denmark are determined by age-specific eating habits, environmental exposures and household structure, rather than being exclusively food-related. These findings are relevant for targeted public health actions and guidelines.

Identification and molecular characteristics of verotoxin-producing Escherichia coli (VTEC) from bovine and pig carcasses isolated in Poland during 2014-2018

The presence of verotoxin-producing Escherichia coli (VTEC) on bovine (n = 330) and pig (n = 120) carcasses in Poland was investigated using the ISO/TS 13136 standard. A total of 115 (34.8%) and 37 (30.8%) cattle and pig samples were positive in real-time PCR, respectively. Isolation of the bacteria revealed that from bovine carcasses 37 (32.2%) VTEC were obtained whereas only 5 (13.5%) pig carcasses were positive for the stx gene. The VTEC were characterized using whole genome sequencing (WGS) and bovine isolates were classified into 25 serotypes with the most prevalent O113:H21 (5 strains) whereas pig strains belonged to 5 different serotypes which were not identified among cattle strains. The majority of bovine VTEC (35; 94.6% isolates) were positive for the stx2 gene, either alone or together with the stx1 gene. All strains isolated from pig carcasses resulted positive for the stx2 gene only. Only two isolates of bovine origin contained the eaeA intimin gene, together with the ehxA and lpfA markers. VTEC were highly molecularly diverse as shown by classification into 29 different MLST STs. The obtained results suggest that further studies related to cattle and pig carcasses are needed to assess the role of these sources for human VTEC infections.

Detection, Prevalence, and Pathogenicity of Non-O157 Shiga Toxin-Producing Escherichia coli from Cattle Hides and Carcasses

Cattle are a major reservoir for Shiga toxin-producing Escherichia coli (STEC) and harbor these bacteria in the intestinal tract. The prevalence, concentration, and STEC serogroup isolated in cattle varies between individuals. Hide removal at slaughter serves as a major point of carcass contamination and ultimately beef products. Certain STEC serogroups, such as O26, O45, O103, O111, O121, O145, and O157, containing the intestinal adherence factor intimin, pose a large economic burden to food producers because of testing and recalls. Human infection with STEC can cause illnesses ranging from diarrhea to hemorrhagic colitis and hemolytic uremic syndrome, and is commonly acquired through ingestion of contaminated foods, often beef products. Previously, most studies focused on O157 STEC, but there is growing recognition of the importance of non-O157 STEC serogroups. This review summarizes detection methods, prevalence, and methods for prediction of pathogenicity of non-O157 STEC from cattle hides and carcasses. A synthesis of procedures is outlined for general non-O157 STEC and targeted detection of specific STEC serogroups. Standardization of sample collection and processing procedures would allow for more robust comparisons among studies. Presence of non-O157 STEC isolated from cattle hides and carcasses and specific factors, such as point of sample collection and season, are summarized. Also, factors that might influence STEC survival on these surfaces, such as the microbial population on hides and microbial adherence genes, are raised as topics for future investigation. Finally, this review gives an overview on studies that have used genetic and cell-based methods to identify specific phenotypes of non-O157 STEC strains isolated from cattle to assess their risk to human health.

Pathogenic and non-pathogenic Escherichia coli colonization and host inflammatory response in a defined microbiota mouse model

Most Escherichia coli strains in the human intestine are harmless. However, enterohemorrhagic Ecoli (EHEC) is a foodborne pathogen that causes intestinal disease in humans. Conventionally reared (CONV) mice are inconsistent models for human infections with EHEC because they are often resistant to Ecoli colonization, in part due to their gastrointestinal (GI) microbiota. Although antibiotic manipulation of the mouse microbiota has been a common means to overcome colonization resistance, these models have limitations. Currently, there are no licensed treatments for clinical EHEC infections and, thus, new tools to study EHEC colonization need to be developed. Here, we used a defined microbiota mouse model, consisting of the altered Schaedler flora (ASF), to characterize intestinal colonization and compare host responses following colonization with EHEC strain 278F2 or non-pathogenic Ecoli strain MG1655. Significantly higher (P<0.05) levels of both strains were found in feces and cecal and colonic contents of C3H/HeN ASF compared to C3H/HeN CONV mice. GI inflammation was significantly elevated (P<0.05) in the cecum of EHEC 278F2-colonized compared to E. coli MG1655-colonized C3H/HeN ASF mice. In addition, EHEC 278F2 differentially modulated inflammatory-associated genes in colonic tissue of C3H/HeN ASF mice compared to E. coli MG1655-colonized mice. This approach allowed for prolonged colonization of the murine GI tract by pathogenic and non-pathogenic Ecoli strains, and for evaluation of host inflammatory processes. Overall, this system can be used as a powerful tool for future studies to assess therapeutics, microbe-microbe interactions, and strategies for preventing EHEC infections.

Comparing Characteristics of Sporadic and Outbreak-Associated Foodborne Illnesses, United States, 2004-2011

Our findings do not warrant rejecting the hypothesis that outbreak and sporadic illnesses are similar.

Comparing Sporadic and Outbreak Foodborne Illness

Outbreak data have been used to estimate the proportion of illnesses attributable to different foods. Applying outbreak-based attribution estimates to nonoutbreak foodborne illnesses requires an assumption of similar exposure pathways for outbreak and sporadic illnesses. This assumption cannot be tested, but other comparisons can assess its veracity. Our study compares demographic, clinical, temporal, and geographic characteristics of outbreak and sporadic illnesses from Campylobacter, Escherichia coli O157, Listeria, and Salmonella bacteria ascertained by the Foodborne Diseases Active Surveillance Network (FoodNet). Differences among FoodNet sites in outbreak and sporadic illnesses might reflect differences in surveillance practices. For Campylobacter, Listeria, and Escherichia coli O157, outbreak and sporadic illnesses are similar for severity, sex, and age. For Salmonella, outbreak and sporadic illnesses are similar for severity and sex. Nevertheless, the percentage of outbreak illnesses in the youngest age category was lower. Therefore, we do not reject the assumption that outbreak and sporadic illnesses are similar.

Estimates of the burden of illness for eight enteric pathogens associated with animal contact in Canada

Enteric pathogens are commonly known to be transmitted through food or water; however, contact with animals is another important transmission route. This study estimated the annual burden of illness attributable to animal contact for eight enteric pathogens in Canada. Using data from a Canadian expert elicitation on transmission routes, the proportion of enteric illnesses attributable to animal contact was estimated for each pathogen to estimate the annual number of illnesses, hospitalizations and deaths in Canada. For each estimate, a mean and probability intervals were generated. Of all illnesses caused by these eight pathogens, 16% were estimated attributable to animal contact. This estimate translates to 86 000 (31 000–166 000) illnesses, 488 (186–890) hospitalizations and 12 (2–28) deaths annually for the eight pathogens combined. Campylobacter spp. is the leading cause of illnesses annually, with an estimated 38 000 (14 000–71 000) illnesses occurring each year, followed by non-typhoidal Salmonella spp. (17 000, 6000–32 000). The majority of hospitalizations were attributable to non-typhoidal Salmonella spp. (36%) and Campylobacter spp. (31%). Non-typhoidal Salmonella spp. (28%) and Listeria monocytogenes (31%) were responsible for the majority of the estimated deaths. These results identify farm animal and pet/pet food exposure as key pathways of transmission for several pathogens. The estimated burden of illness associated with animal contact is substantial.

Prevalence and Level of Enterohemorrhagic Escherichia coli in Culled Dairy Cows at Harvest

The primary objective of this study was to determine the prevalence and level of enterohemorrhagic Escherichia coli (EHEC) O26, O45, O103, O111, O121, and O145 (collectively EHEC-6) plus EHEC O157 in fecal, hide, and preintervention carcass surface samples from culled dairy cows. Matched samples (n = 300) were collected from 100 cows at harvest and tested by a culture-based method and two molecular methods: NeoSEEK STEC (NS) and Atlas STEC EG2 Combo. Both the culture and NS methods can be used to discriminate among the seven EHEC types (EHEC-7), from which the cumulative prevalence was inferred, whereas the Atlas method can discriminate only between EHEC O157 and non-O157 EHEC, without discrimination of the serogroup. The EHEC-7 prevalence in feces, hides, and carcass surfaces was 6.5, 15.6, and 1.0%, respectively, with the culture method and 25.9, 64.9, and 7.0%, respectively, with the NS method. With the Atlas method, the prevalence of non-O157 EHEC was 29.1, 38.3, and 28.0% and that of EHEC O157 was 29.1, 57.0, and 3.0% for feces, hides, and carcasses, respectively. Only two samples (a hide sample and a fecal sample) originating from different cows contained quantifiable EHEC. In both samples, the isolates were identified as EHEC O157, with 4.7 CFU/1,000 cm(2) in the hide sample and 3.9 log CFU/g in the fecal sample. Moderate agreement was found between culture and NS results for detection of EHEC O26 (κ = 0.58, P < 0.001), EHEC O121 (κ = 0.50, P < 0.001), and EHEC O157 (κ = 0.40, P < 0.001). No significant agreement was observed between NS and Atlas results or between culture and Atlas results. Detection of an EHEC serogroup in fecal samples was significantly associated with detection of the same EHEC serogroup in hide samples for EHEC O26 (P = 0.001), EHEC O111 (P = 0.002), EHEC O121 (P < 0.001), and EHEC-6 (P = 0.029) based on NS detection and for EHEC O121 (P < 0.001) based on detection by culture. This study provides evidence that non-O157 EHEC are ubiquitous on hides of culled dairy cattle and that feces are an important source of non-O157 EHEC hide contamination.

Estimating the burden of acute gastrointestinal illness due to Giardia, Cryptosporidium, Campylobacter, E. coli O157 and norovirus associated with private wells and small water systems in Canada

Waterborne illness related to the consumption of contaminated or inadequately treated water is a global public health concern. Although the magnitude of drinking water-related illnesses in developed countries is lower than that observed in developing regions of the world, drinking water is still responsible for a proportion of all cases of acute gastrointestinal illness (AGI) in Canada. The estimated burden of endemic AGI in Canada is 20·5 million cases annually – this estimate accounts for under-reporting and under-diagnosis. About 4 million of these cases are domestically acquired and foodborne, yet the proportion of waterborne cases is unknown. There is evidence that individuals served by private systems and small community systems may be more at risk of waterborne illness than those served by municipal drinking water systems in Canada. However, little is known regarding the contribution of these systems to the overall drinking water-related AGI burden in Canada. Private water supplies serve an estimated 12% of the Canadian population, or ~4·1 million people. An estimated 1·4 million (4·1%) people in Canada are served by small groundwater (2·6%) and surface water (1·5%) supplies. The objective of this research is to estimate the number of AGI cases attributable to water consumption from these supplies in Canada using a quantitative microbial risk assessment (QMRA) approach. This provides a framework for others to develop burden of waterborne illness estimates for small water supplies. A multi-pathogen QMRA of Giardia, Cryptosporidium, Campylobacter, E. coli O157 and norovirus, chosen as index waterborne pathogens, for various source water and treatment combinations was performed. It is estimated that 103 230 AGI cases per year are due to the presence of these five pathogens in drinking water from private and small community water systems in Canada. In addition to providing a mechanism to assess the potential burden of AGI attributed to small systems and private well water in Canada, this research supports the use of QMRA as an effective source attribution tool when there is a lack of randomized controlled trial data to evaluate the public health risk of an exposure source. QMRA is also a powerful tool for identifying existing knowledge gaps on the national scale to inform future surveillance and research efforts.

Highly Virulent Non-O157 Enterohemorrhagic Escherichia coli (EHEC) Serotypes Reflect Similar Phylogenetic Lineages, Providing New Insights into the Evolution of EHEC

Enterohemorrhagic Escherichia coli (EHEC) is the causative agent of bloody diarrhea and extraintestinal sequelae in humans, most importantly hemolytic-uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Besides the bacteriophage-encoded Shiga toxin gene (stx), EHEC harbors the locus of enterocyte effacement (LEE), which confers the ability to cause attaching and effacing lesions. Currently, the vast majority of EHEC infections are caused by strains belonging to five O serogroups (the “big five”), which, in addition to O157, the most important, comprise O26, O103, O111, and O145. We hypothesize that these four non-O157 EHEC serotypes differ in their phylogenies. To test this hypothesis, we used multilocus sequence typing (MLST) to analyze a large collection of 250 isolates of these four O serogroups, which were isolated from diseased as well as healthy humans and cattle between 1952 and 2009. The majority of the EHEC isolates of O serogroups O26 and O111 clustered into one sequence type complex, STC29. Isolates of O103 clustered mainly in STC20, and most isolates of O145 were found within STC32. In addition to these EHEC strains, STC29 also included stx-negative E. coli strains, termed atypical enteropathogenic E. coli (aEPEC), yet another intestinal pathogenic E. coli group. The finding that aEPEC and EHEC isolates of non-O157 O serogroups share the same phylogeny suggests an ongoing microevolutionary scenario in which the phage-encoded Shiga toxin gene stx is transferred between aEPEC and EHEC. As a consequence, aEPEC strains of STC29 can be regarded as post- or pre-EHEC isolates. Therefore, STC29 incorporates phylogenetic information useful for unraveling the evolution of EHEC.