The role of the Public Health Laboratory Service in England and Wales in the investigation of human listeriosis during the 1980s and 1990s

Implicated Food Products for Listeriosis and Changes in Serovars of Listeria monocytogenes Affecting Humans in Recent Decades

Listeriosis is a foodborne disease with a high fatality rate, and infection is mostly transmitted through ready-to-eat (RTE) foods contaminated with Listeria monocytogenes, such as gravad/smoked fish, soft cheeses, and sliced processed delicatessen (deli) meat. Food products/dishes stored in vacuum or in modified atmospheres and with extended refrigerator shelf lives provide an opportunity for L. monocytogenes to multiply to large numbers toward the end of the shelf life. Elderly, pregnant women, neonates, and immunocompromised individuals are particularly susceptible to L. monocytogenes. Listeriosis in humans manifests primarily as septicemia, meningitis, encephalitis, gastrointestinal infection, and abortion. In the mid 1990s and early 2000s a shift from L. monocytogenes serovar 4b to serovar 1/2a causing human listeriosis occurred, and serovar 1/2a is becoming more frequently linked to outbreaks of listeriosis, particularly in Europe and Northern America. Consumer lifestyle has changed, and less time is available for food preparation. Modern lifestyle has markedly changed eating habits worldwide, with a consequent increased demand for RTE foods; therefore, more RTE and take away foods are consumed. There is a concern that many Listeria outbreaks are reported from hospitals. Therefore, it is vitally important that foods (especially cooked and chilled) delivered to hospitals and residential homes for senior citizens and elderly people are reheated to at least 72°C: cold food, such as turkey deli meat and cold-smoked and gravad salmon should be free from L. monocytogenes. Several countries have zero tolerance for RTE foods that support the growth of Listeria.

Application of Hazard Analysis and Critical Control Point Methodology and Risk-Based Grading to Consumer Food Safety Surveys

Traditionally, consumer food safety survey responses have been classified as either “right” or “wrong” and food handling practices that are associated with high risk of infection have been treated in the same way as practices with lower risks. In this study, a risk-based method for consumer food safety surveys has been developed, and HACCP (hazard analysis and critical control point) methodology was used for selecting relevant questions. We conducted a nationally representative Web-based survey (n = 2,008), and to fit the self-reported answers we adjusted a risk-based grading system originally developed for observational studies. The results of the survey were analyzed both with the traditional “right” and “wrong” classification and with the risk-based grading system. The results using the two methods were very different. Only 5 of the 10 most frequent food handling violations were among the 10 practices associated with the highest risk. These 10 practices dealt with different aspects of heat treatment (lacking or insufficient), whereas the majority of the most frequent violations involved storing food at room temperature for too long. Use of the risk-based grading system for survey responses gave a more realistic picture of risks associated with domestic food handling practices. The method highlighted important violations and minor errors, which are performed by most people and are not associated with significant risk. Surveys built on a HACCP-based approach with risk-based grading will contribute to a better understanding of domestic food handling practices and will be of great value for targeted information and educational activities.

Isolation and characterization of Listeria monocytogenes and other Listeria species in foods of animal origin in Addis Ababa, Ethiopia

Listeriosis is a disease of humans and animals, in which it is one of the important emerging bacterial zoonotic diseases worldwide. Among the different species of the genus Listeria, Listeria monocytogenes (L. monocytogenes) is known to cause listeriosis in humans and animals with low incidence but high case fatality rate. Information on the occurrence and distribution of L. monocytogenes and other Listeria species is very limited both in the veterinary and public health sectors in Ethiopia. The objective of this study was to isolate and characterize L. monocytogenes and other Listeria species from foods of animal origin (cottage cheese, raw beef, raw milk and liquid whole egg) in Addis Ababa, Ethiopia. A total of 391 food samples of animal origin were collected randomly, using a cross-sectional study design from November 2008 to March 2009. L. monocytogenes isolation and characterization were performed according to mainly the United States Food and Drug Administration procedures. Of the samples examined, 102 (26.1%) were found to be positive for Listeria. Listeria species were isolated in 39 (51.3%), 37 (32.2%), 22 (22%) and 4 (4%) of the raw beef, liquid whole egg, raw milk and cottage cheese samples respectively. L. monocytogenes was detected in 5.4% of the samples analyzed. It was isolated mainly from raw milk (13%) and liquid whole egg (4.3%) followed by raw beef (2.6%) and cottage cheese (1%). In addition to L. monocytogenes, other Listeria species were identified as L. innocua (60.8%), L. welshimeri (6.9%), L. seeligeri (3.9%), L. murrayi (2.9%) and L. grayi (2.9%) and L. ivanovii (1.9%). It was shown that L. monocytogenes and other Listeria species are widely spread in occurrence in foods of animal origin in Addis Ababa, Ethiopia.

Survival of Listeria monocytogenes Scott A on metal surfaces: implications for cross-contamination

Listeria monocytogenes is an important re-emerging pathogen which is commonly found in the environment. Many outbreaks have been associated with the contamination of food produce, often linked to cross-contamination from surfaces or equipment to prepared foodstuffs. In the present study a number of copper-base metal alloys have been used to assess the survival times of L. monocytogenes on different materials, in comparison with stainless steel. High concentrations (10(7)) of bacteria were placed on metal coupons cut from each alloy. After defined incubation times, coupons were placed in tubes containing phosphate buffered saline and vortexed to remove the cells. Aliquots were then plated onto tryptone blood agar plates and the number of colony forming units counted. The high concentration of bacteria was used to represent a "worst-case" scenario. The results indicate that survival is greatly reduced on a copper-base alloy compared to stainless steel. Viable cells could be detected on stainless steel after 24 h incubation at room temperature. On copper, brass, aluminium bronze and silicon bronze, no viable bacteria could be detected after 60 min incubation, indicating a 5 log reduction (the detection limit of the procedure was 100 bacteria). No cells could be detected from copper nickel and copper nickel zinc alloys, after 90 min incubation. The viability stain, 5-cyano-2,3-ditolyl tetrazolium chloride (CTC), confirmed these results, with actively respiring bacteria being clearly labelled on stainless steel after 24 h. The results suggest that careful choice of surface material could reduce the potential risk of cross-contamination in industrial, commercial and domestic environments.

Listeria monocytogenes and listeriosis: a review of hazard characterisation for use in microbiological risk assessment of foods

Considerable effort has been put into the application of quantitative microbiological risk assessment for Listeria monocytogenes, and data are available for England and Wales (probably more so than most other countries) on the adverse health effects, together with incidence data on different age and risk groups for human L. monocytogenes infections. This paper reviews aspects of Listeria and human listeriosis, especially from a public health perspective and provide hazard characterisation data, i.e. the qualitative and/or quantitative evaluation of the adverse health effect associated with the hazard, which is the relationship between exposure levels (dose) and frequency of illness. The majority of cases of human listeriosis are food-borne; however, the disease process is complex with multiple routes of infection. The dose-response relationship is poorly understood, and data from human volunteer studies are not available and would be unethical to produce. Data are available from a range of different animal and in vitro models, although these poorly mimic the natural disease process in route of infection, end point, host and history of prior exposure to the bacterium. Epidemiological data provide some information on infective doses and dose responses, but because of the characteristics of the disease (the hugely variable and potentially very long incubation periods, the low attack rates and the rarity of identification of specific food vehicles), this also provides limited data for calculation of dose responses. There is some, albeit limited, evidence for strain variation, but this is an area of considerable uncertainty despite great advances in the genetic basis of the virulence of this bacterium, and almost all strains seem capable of causing serious disease. A variety of mathematical approaches have been used to model dose responses. The review is written to provide a clinical and epidemiological background to the mathematically oriented, as well as to outline the mathematical approaches to those interested in food-borne infection.

Listeria monocytogenes occurrence and characterization in meat-producing plants

AIMS

The prevalence, level of contamination and epidemiological profile of Listeria monocytogenes were investigated in two meat-producing plants during a 20-month period.

METHODS AND RESULTS

Sampling for L. monocytogenes was carried out in a cattle slaughterhouse (n = 72) and a swine meat-processing plant (n = 68) during a 20-month period. Swabs and food samples were analysed with the most probable number (MPN) technique for L. monocytogenes and the isolated strains were characterized by AscI-restriction analysis pulsed-field gel electrophoresis (REA-PFGE). Contamination of meat and meat products was always at low level (below 50 MPN per gram). The seven L. monocytogenes positive samples isolated in the bovine slaughterhouse yielded strains with the same REA-PFGE profile. However, the seven strains isolated in the swine meat processing plant showed six different profiles. Two of them showed indistinguishable profiles with L. monocytogenes strains collected from other meat processing facilities located in the same area.

SIGNIFICANCE AND IMPACT OF THE STUDY

The genotyping method is a valuable tool to investigate contamination sources. The study of REA-PFGE profiles indicated that environmental contamination was probably responsible for the persistence of over 16 months of one strain of L. monocytogenes in the cattle slaughterhouse. Several meat suppliers could be responsible for the contamination in the pig meat processing facility, and this is confirmed by the finding of some identical strain in other meat processing facilities located in the same area.

Listeriosis

Listeria monocytogenes is ubiquitous in nature and is part of the normal flora of the distal portion of the intestinal tract of numerous animal species. Listeriosis is an emerging food borne disease that is responsible for approximately 1,700 cases of human illness each year and 650 deaths. Listeria is the cause of three main disease entities in animals and humans: neural, visceral, and reproductive. Clinical signs associated with the three forms are discussed along with diagnosis, therapy, prevention, and control.