Kathie Grant

Changing Pattern of Human Listeriosis, England and Wales, 2001–2004

Disease has reemerged, mainly in patients ≥60 years of age with bacteremia.

Whole genome-based population biology and epidemiological surveillance of Listeria monocytogenes

Listeria monocytogenes (Lm) is a major human foodborne pathogen. Numerous Lm outbreaks have been reported worldwide and associated with a high case fatality rate, reinforcing the need for strongly coordinated surveillance and outbreak control. We developed a universally applicable genome-wide strain genotyping approach and investigated the population diversity of Lm using 1,696 isolates from diverse sources and geographical locations. We define, with unprecedented precision, the population structure of Lm, demonstrate the occurrence of international circulation of strains and reveal the extent of heterogeneity in virulence and stress resistance genomic features among clinical and food isolates. Using historical isolates, we show that the evolutionary rate of Lm from lineage I and lineage II is low (∼2.5 × 10−7 substitutions per site per year, as inferred from the core genome) and that major sublineages (corresponding to so-called ‘epidemic clones’) are estimated to be at least 50–150 years old. This work demonstrates the urgent need to monitor Lm strains at the global level and provides the unified approach needed for global harmonization of Lm genome-based typing and population biology.

The microbiological safety of ready-to-eat specialty meats from markets and specialty food shops: a UK wide study with a focus on Salmonella and Listeria monocytogenes.

From 2359 specialty meats (continental sausages, cured/fermented, dried meats) sampled from markets and specialty food shops, 98.9% of samples were of satisfactory or acceptable microbiological quality. However, 16 (0.7%) were unsatisfactory as a result of Escherichia coli, Staphylococcus aureus or Listeria spp. contamination (>or=10(2) CFU/g), and nine (0.4%) were unacceptable due to presence of Salmonella spp. or Listeria monocytogenes (>10(2) CFU/g). Meats with unacceptable levels of L. monocytogenes were within shelf life (range: 8-143 days remaining). Nine different subtypes of L. monocytogenes were detected with sero/AFLP type 1/2c VII predominating (37%), although this subtype was not overrepresented in any particular meat type (P > 0.05). Ninety-six percent of continental sausages and cured/fermented products were stored at <8 degrees C at premises, including seven of the nine unacceptable samples. These nine meats were all pre-packed prior to supply to retail premises (OR = 0.1 P = 0.003) indicating that contamination with bacterial pathogens occurred earlier in the production chain. Most samples (72.7%, 8/11) with unsatisfactory levels of E. coli were sliced on request, suggesting cross-contamination at point of sale. This study highlights the importance of ensuring that products do not become contaminated before final packaging, that storage conditions are controlled, and that durability dates are an accurate indication of the shelf life of the product so as to minimise the potential for L. monocytogenes to be present at levels hazardous to health at the point of sale.

Disease Presentation in Relation to Infection Foci for Non-Pregnancy-Associated Human Listeriosis in England and Wales, 2001 to 2007

ABSTRACT Listeriosis is a rare but severe food-borne disease, affecting unborn or newly delivered infants, the elderly, and the immunocompromised. The epidemiology of listeriosis in England and Wales changed between 2001 and 2007, with more patients ≥60 years old presenting with bacteremia (but without central nervous system [CNS] involvement). In order to explain this increase and understand the altered disease presentation, clinical, microbiological, and seasonal data on bacteremic cases of Listeria monocytogenes infection identified through national surveillance were compared with those for patients with CNS infections. Logistic regression analysis was applied while controlling for age. Bacteremic patients, who presented more frequently with gastrointestinal symptoms, were more likely to have underlying medical conditions than CNS patients. This was most marked in patients with malignancies, particularly digestive organ malignancies. Treatment to reduce stomach acid secretion modified the effect of nonmalignant underlying conditions on outcome, i.e., patients with an underlying condition who were not taking acid-suppressing medication were equally likely to have a bacteremic or a CNS infection. However, this type of therapy did not modify the effect of malignancies on the likelihood of having a bacteremic or a CNS infection. The increase in the incidence of human listeriosis among patients ≥60 years old in England and Wales between 2001 and 2007 appears to have occurred in those with cancer or other conditions whose treatment included acid-suppressing medication. Therefore, this vulnerable patient group needs specific dietary advice on avoiding risk factors for listeriosis.

Characterization of a Verocytotoxin-Producing Enteroaggregative Escherichia coli Serogroup O111:H21 Strain Associated with a Household Outbreak in Northern Ireland

ABSTRACT A strain of Escherichia coli O111:H21 recently isolated in the United Kingdom harbored the phage-encoded vtx2c gene and the aggregative adherence plasmid. Although exhibiting the same pathogenic profile as the E. coli O104:H4 strain linked to the outbreak in Germany, there were important differences in strain characteristics and in the epidemiological setting.

Attribution of human Listeria monocytogenes infections in England and Wales to ready-to-eat food sources placed on the market: adaptation of the Hald Salmonella source attribution model.

Human listeriosis is a rare but serious foodborne disease, with high morbidity and mortality in vulnerable populations (e.g., pregnant women, the elderly, and the immunocompromised). The disease is predominantly caused by the consumption of contaminated ready-to-eat foods. Since 2001, an increase in the number of listeriosis cases has been observed in several European Union countries, including England and Wales, predominantly in the over-60s population. The cause of this selective increased incidence is unknown. The Hald Salmonella Bayesian source attribution model was adapted to determine the potential of this approach to quantify the contribution of different food sources to the burden of human listeriosis in England and Wales from 2004 to 2007. The most important food sources for the overall population were multicomponent foods (sandwiches and prepacked mixed salad vegetables) (23.1%), finfish (16.8%), and beef (15.3%). Attribution of major sources of infection was similar for the elderly population (>or=60 years old, multicomponent foods [22.0%], finfish [14.7%], and beef [13.6%]). For pregnancy-associated cases, beef (12.3%), milk and milk products (11.8%), and finfish (11.2%) were more important sources of infection. The adapted model also showed that the serotype 4b was associated with relatively more human infections than that of other serotypes; further, the subtype 4b amplified fragment-length polymorphism V was associated with more pregnancy-associated cases than other subtypes of 4b. This approach of quantifying the contribution of various food sources to human listeriosis provides a useful tool in food safety risk analysis, and underlines the need for further emphasis to be given to the reduction of Listeria monocytogenes in high-risk foods, such as multicomponent foods, which are consumed without any further treatment. The need for targeted dietary advice for the elderly population is also highlighted.

The identification and characterization of Clostridium perfringens by real-time PCR, location of enterotoxin gene, and heat resistance.

Clostridium perfringens carrying the enterotoxin gene is an important cause of both foodborne and non-foodborne diarrheal disease. Rapid identification of isolates carrying the enterotoxin gene is invaluable for outbreak investigation whilst information on the genomic location of the enterotoxin (cpe) gene can improve our understanding of disease transmission. This paper describes the validation of a real-time polymerase chain reaction (PCR) assay for the identification of C. perfringens and assessment of the potential to cause diarrhea, together with an investigation into the genomic location of the cpe genes in isolates from confirmed incidents of C. perfringens diarrhea. The real-time assay was shown to be specific for the identification of 253 C. perfringens cultures and gave results concordant with those from motility nitrate and lactose gelatine media, the Nagler reaction, and a conventional block-based PCR assay. The cpe gene was detected in 223 of 253 C. perfringens cultures isolated in association with human gastrointestinal disease. A subset of cpe-positive C. perfringens isolates associated with separate incidents of diarrheal disease were investigated further for plasmid or chromosomal location of the cpe gene using a multiplex PCR assay. The cpe gene was plasmid encoded in two isolates from cases of sporadic diarrhea and six isolates from cases of food poisoning. The cpe gene from the remaining 11 isolates from different food poisoning outbreaks was found to be chromosomally encoded. One of the C. perfringens strains with a plasmid encoded cpe gene formed spores of high heat resistance and five formed spores that were sensitive to heating. Eight of the isolates with a chromosomal cpe gene formed heat-resistant spores, and two formed spores with an intermediate heat resistance.

Outbreak of Listeria monocytogenes in an oncology unit associated with sandwiches consumed in hospital

In May 2003, two adult patients in an oncology unit were diagnosed with listeriosis, and sandwiches consumed in the hospital were identified as a common risk factor. Both patients were infected by the same strain of Listeria monocytogenes. Sandwiches collected from the hospital and external sandwich producer, as well as sites within the manufacturing environment, were contaminated by the same strain of L. monocytogenes. Sandwiches consumed in other hospitals have been associated with small clusters of listeriosis patients in the UK. This report describes the investigations following diagnosis of the two infections, and highlights a more general problem with sandwiches sold in hospitals.

Listeria monocytogenes infection in the over-60s in England between 2005 and 2008: a retrospective case-control study utilizing market research panel data.

A retrospective case-control study of listeriosis in patients in England aged over 60 years is described. The incidence of listeriosis in patients aged ≥60 years in England has doubled since 2001; hence, the investigation of risk factors for infection in this group is important to inform on prevention and control. Standardized epidemiological information has been sought on cases since 2005, but the value of the data accrued is limited without some perception of exposure prevalence in the population at risk of listeriosis. The exposures of listeriosis cases aged ≥60 years reported in England from 2005 to 2008 were compared to those of market research panel members representing the same population (i.e., residents of England aged ≥60 years) and time period. Exposures were grouped to facilitate comparison. Odds ratios and 95% confidence intervals were calculated. Cases were more likely than panel members to report the consumption of cooked meats (beef and ham/pork, but not poultry), cooked fish (specifically smoked salmon) and shellfish (prawns), dairy products (most noticeably milk but also certain cheeses), and mixed salads. They were less likely to report the consumption of other forms of seafood, dairy spread, other forms of dairy, sandwiches, and fresh vegetables. The diversity of high-risk food exposures reflects the ubiquity of the microorganism in the environment and/or the susceptibility of those at risk, and suggests that a wider variety of foods can give rise to listeriosis. Food safety advice on avoiding listeriosis should be adapted accordingly. While not inexpensive, the application of market research data to infectious disease epidemiology can add value to routine surveillance data.

Fluorescence amplified fragment length polymorphism compared to pulsed field gel electrophoresis for Listeria monocytogenes subtyping.

BackgroundListeriosis is a severe infection which mainly affects pregnant women, neonates and immuno-compromised adults. ANSES’s Laboratory for Food safety has been the European Union Reference Laboratory (EURL) for L. monocytogenes in the food chain since 2006. Pulsed Field Gel Electrophoresis (PFGE) is routinely used in the EURL for the surveillance of L. monocytogenes isolated from foods, animals and the environment. One of the main EURL activities is to evaluate alternative molecular subtyping methods to PFGE, and integrate their use within the National Reference Laboratories (NRL) network. Since 2008, the United Kingdom (UK)-NRL for L. monocytogenes at the Health Protection Agency (HPA), London, has used fluorescent Amplified Fragment Length Polymorphism (fAFLP) for the routine surveillance of L. monocytogenes isolated from human clinical cases, food and food processing environments in the UK. This study compares fAFLP with PFGE for subtyping L. monocytogenes.ResultsA panel of 109 L. monocytogenes isolates from either human cases of listeriosis, foods, food processing environments and animals were used for the comparative evaluation. Among these, 2 strains were tested from duplicate culture by both methods. The panel also included field isolates, isolates associated with outbreaks or sporadic cases and reference strains. The two strains tested in duplicate displayed the same fAFLP and PFGE types. Strains known to be epidemiologically associated with one another were found to have unique PFGE and fAFLP types. FAFLP and PFGE divided the strains into 76 and 82 distinct profiles, or types, respectively. The discriminatory index calculated was 0.993 and 0.996 for fAFLP and PFGE, respectively.ConclusionsThe discriminatory ability of fAFLP was similar to that of PFGE for the subtyping of L. monocytogenes isolates. As a less labour intensive technique fAFLP may be a better method to use than PFGE in investigating outbreaks of human listeriosis and tracking the source of contamination in food processing facilities in real time.