Microbiological and epidemiological investigation of the Neisseria meningitidis serogroup A epidemic in Niger in 2009: last wave before the introduction of the serogroup A meningococcal conjugate vaccine?

The 2009 meningitis season in Niger was characterized by an early onset, beginning in the very first weeks of the year and peaking from the 12th to the 15th week with 5655 clinical cases over the 4 weeks. From 1 January 2009 to 28 June 2009 (week 26), a total of 13,733 clinical cases of meningitis were reported to the national epidemiological surveillance system with a case-fatality rate of 4·2%. During the season 25 of the 42 health districts reached the epidemic threshold and 11 the alert threshold. Reactive mass vaccination campaigns involving a total of 5 166,741 doses of the polysaccharide meningococcal bivalent (A+C) vaccine progressively controlled the outbreak in most parts of the country. A total of 3755 cerebrospinal fluid samples representing 28·1% of the suspected meningitis cases were analysed. Serogroup A meningococci were the causative agent in 97·5% of the meningococcal cases. Multi-locus sequence typing of 26 meningococal serogroup A strains showed 25 sequence type (ST)7 and one ST2859, both sequence types belonging to the ST5 clonal complex (CC5) of subgroup III. This is the largest epidemic observed in Niger since those of 1995-1996 (59,948 notified cases) and 2000 (14,633 notified cases).

Quantitative risk assessment of Listeria monocytogenes in ready-to-eat foods: the FAO/WHO approach.

Quantitative microbiological risk assessment is a very new and unique scientific approach able to link, for the first time, data from food (in the farm-to-fork continuum) and the various data on human disease to provide a clear estimation of the impact of contaminated food on human public health. The Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) have recently launched risk assessment studies of a number of pathogen-food commodity combinations (Salmonella in eggs and in broiler chickens, Listeria monocytogenes in ready-to-eat foods, Campylobacter in broiler chickens, Vibrio in seafood) to be used to lower the risk associated with these food-borne diseases and ensure fair practices in the international trade of food. The FAO/WHO Listeria risk assessment was undertaken in part to determine how previously developed risk assessments done at the national level could be adapted or expanded to address concerns related to L. monocytogenes in ready-to-eat foods at an international level. In addition, after initiation of the risk assessment, the risk assessors were asked by the Codex Committee on Food to consider three specific questions related to ready-to-eat foods in general, which are: (1). estimate the risk for consumers in different susceptible populations groups (elderly, infants, pregnant women and immunocompromised patients) relative to the general population; (2). estimate the risk for L. monocytogenes in foods that support growth and foods that do not support growth under specific storage and shelf-life conditions; (3). estimate the risk from L. monocytogenes in food when the number of organisms ranges from absence in 25 g to 1000 colonies forming units per gram or milliliter, or does not exceed specified levels at the point of consumption. To achieve these goals, new dose-response relationships and exposure assessments for ready-to-eat foods were developed. Preliminary data indicate that eliminating the higher dose levels at the time of consumption has a large impact on the number of predicted cases.

Expression of ActA, Ami, InlB, and listeriolysin O in Listeria monocytogenes of human and food origin.

Expression of proteins involved in the adhesion of Listeria monocytogenes to mammalian cells or in the intracellular life cycle of this bacterium, including listeriolysin O (LLO), ActA, Ami, and InlB, was used to compare two populations of L. monocytogenes strains. One of the populations comprised 300 clinical strains, and the other comprised 150 food strains. All strains expressed LLO, InlB, and ActA. No polymorphism was observed for LLO and InlB. Ami was detected in 283 of 300 human strains and in 149 of 150 food strains. The strains in which Ami was not detected were serovar 4b strains. Based on the molecular weights of the proteins detected, the strains were divided into two groups with Ami (groups Ami1 [75% of the strains] and Ami2 [21%]) and into four groups with ActA (groups ActA1 [52% of the strains], ActA2 [18%], ActA3 [30%], and ActA4 [one strain isolated from food]). Logistic regression showed that food strains were more likely to belong to group ActA3 than human strains (odds ratio [OR] = 2.90; P = 1 x 10(-4)). Of the strains isolated from patients with non-pregnancy-related cases of listeriosis, bacteremia was predominantly associated with group Ami1 strains (OR = 1.89; P = 1 x 10(-2)) and central nervous system infections were associated with group ActA2 strains (OR = 3.04; P = 1 x 10(-3)) and group ActA3 strains (OR = 3.91; P = 1 x 10(-3)).

Multicenter study of street foods in 13 towns on four continents by the food and environmental hygiene study group of the international network of pasteur and associated institutes.

An international multicenter study of ready-to-eat foods, sandwiches, and ice creams or sorbets sold in the streets and their vendors was carried out to assess the microbiological quality of these foods and to identify characteristics of the vendors possibly associated with pathogens. Thirteen towns in Africa, America, Asia, and Oceania were involved in the study. A single protocol was used in all 13 centers: representative sampling was by random selection of vendors and a sample of foods bought from each of these vendors at a time and date selected at random. Microbiological analyses were carried out using standardized Association Française de Normalisation methods, and the use of a standardized questionnaire to collect data concerning the characteristics of the vendors. Fifteen surveys were carried out, with 3,003 food samples from 1,268 vendors. The proportion of unsatisfactory food samples was between 12.7 and 82.9% for ice creams and sorbets and between 11.3 and 92% for sandwiches. For ice creams and sorbets, the sale of a large number of units (>80 per day) increased the risk of unsatisfactory food by a factor of 2.8 (95% confidence interval [CI]: 1.5 to 5.1), lack of training in food hygiene by 6.6 (95% CI: 1.1 to 50). and by a factor of 2.8 (95% CI: 1.4 to 5.4) for mobile vendors. These risk factors were not identified for sandwiches, this difference may be due to the presence of a cooking step in their preparation. These results show that the poor microbiological quality of these street foods constitutes a potential hazard to public health, that the extent of this hazard varies between the cities studied, and that vendors' health education in food safety is a crucial factor in the prevention of foodborne infections.

Effect of prevention measures on incidence of human listeriosis, France, 1987-1997.

To assess the impact of preventive measures by the food industry, we analyzed food monitoring data as well as trends in the incidence of listeriosis estimated through three independent sources: the National Reference Center of Listeriosis; a laboratory-based active surveillance network; and two consecutive nationwide surveys of public hospital laboratories. From 1987 to 1997, the incidence of listeriosis decreased by an estimated 68%. A substantial reduction in the proportion of Listeria monocytogenes-contaminated products was observed at the retail level. The temporal relationship between prevention measures by the food industry, reduction in L. monocytogenes-contaminated foodstuffs, and reduction in listeriosis incidence suggests a causal relationship and indicates that a substantial part of the reduction in illness is related to prevention efforts.

Two consecutive nationwide outbreaks of Listeriosis in France, October 1999-February 2000.

In France, listeriosis surveillance is based on mandatory notification of all culture-confirmed cases, with systematic typing of isolates and routine collection of the patient's food history. From October 1999 to March 2000, two outbreaks of listeriosis were detected through this enhanced surveillance system. In outbreak 1, analysis of the food histories of cases suggested brand X "rillettes," a pâté-like meat product, as the vehicle of infection, and the outbreak strain of Listeria monocytogenes was subsequently isolated from the incriminated rillettes. In outbreak 2, a case-control study showed that consumption of jellied pork tongue was strongly associated with infection with the outbreak strain (odds ratio = 75.5, 95% confidence interval: 4.7, 1,216.0). However, trace-back results did not permit incrimination of any particular manufacturer of jellied pork tongue, and the outbreak strain was not isolated from the incriminated food or from any production sites. Consumption of jellied pork tongue was discouraged on epidemiologic evidence alone. The consecutive occurrence of these two outbreaks confirms the epidemic potential of listeriosis, even in a context of decreasing incidence, and underlines the importance of timely case-reporting and systematic typing of human L. monocytogenes strains to allow early detection and separate investigation of different clusters.

Can food-related environmental factors induce different behaviour in two key serovars, 4b and 1/2a, of Listeria monocytogenes?

Listeria monocytogenes isolates (81 in total; 42 isolated from cases of human listeriosis: 39 isolated from food), belonging to serovars 1/2a or 4b, were studied for any group differences between serovars to selected factors associated with foods (two bacteriocins and mild heat treatment), growth kinetics at 37 degrees C and pathogenicity for chick embryos. The isolates were tested for sensitivity to two bacteriocins at 4 degrees C and 37 degrees C, and were tested for the remaining parameters both before and after exposure to cold storage (4 degrees C) with starvation. In addition, the isolates were typed using pulsed field gel electrophoresis (PFGE), multilocus enzyme electrophoresis (MEE) and phage typing to find any correlation between the types and group differences in the chosen parameters. Considerable strain diversity within each L. monocytogenes serovar with respect to the chosen parameters was observed, especially after exposure to cold storage. Nevertheless, the serovar 1/2a isolates, as a group, tended to be more resistant to the two antilisterial bacteriocins at 4 degrees C than the group of serovar 4b isolates. In contrast, after cold storage at 4 degrees C, L. monocytogenes serovar 4b isolates, as a group, tended to be more resistant to heat treatment at 60 degrees C than the group of 1/2a isolates. In addition, the serovar 4b group tended to have shorter lag phases and higher pathogenicity, when transferred from cold storage to body temperature (37 degrees C), than the group of serovar 1/2a isolates. No correlation between PFGE-, MEE- and phage-types and the tested parameters was found. Although the above serovar-related differences were observed only when mean values of the groups were compared (not all isolates within each group followed the group pattern), the results indicate interesting directions for further research.

Occurrence of Listeria monocytogenes in food in Chile.

Out of 2145 food samples analysed 77 were found contaminated with Listeria monocytogenes in Santiago, Chile. Samples were: 603 ice-cream (3.5% contaminated), 256 soft cheese (0.8%), 155 hard cheese (0%), 229 baby milk bottles (0%), 634 processed meat products (3.6%) and 268 crustaceous shellfish (11.6%). Three different isolation media were used: for 318 samples, Modified McBride Agar (MMA), Lithium chloride Phenylethanol Moxalactam agar, and Polymyxin Acriflavine Lithium chloride Ceftazidime Aesculin Mannitol agar; for 1827 samples MMA was replaced by Listeria Selective Agar Oxford Formulation. Isolates were classified as follow: serovar 1/2a (25 isolates), serovar 4b (20), serovar 1/2b (19), serovar 3b (7), serovar 1/2c (2), untypable (4). A high variety of phagovars was detected although 52% of strains was untypable.

Epidemiology of human listeriosis and seafoods.

While rarely diagnosed prior to 1960, more than 10,000 cases of listeriosis were recorded in the medical literature between 1960 and 1982, and thousands more have been reported annually world-wide [Rocourt J., 1991. Human listeriosis, 1989. WHO/HPP/FOS/91.3, World Health Organization, Geneva, Switzerland; Rocourt, J., Brosch, R., 1992. Human listeriosis, 1990. WHO/HPP/FOS/92.3, World Health Organization, Geneva, Switzerland; Rocourt, J., Jacquet, Ch., Bille, J., 1997. Human listeriosis, 1991/1992. WHO/FNU/FOS/97.1, World Health Organization, Geneva, Switzerland]. This widespread increase in reporting is most likely due to demographic trends and changes in food production, processing and storage, especially the extended cold food chain and the ability of Listeria monocytogenes to grow at low temperatures: L. monocytogenes is a bacterium responsible for opportunistic infections, preferentially affecting individuals whose immune system is perturbed, including pregnant women, newborns, people over 65 years, immunocompromised patients, such as cancer victims, transplant recipients, people on hemodialysis and AIDS patients. Thus, the increasing lifespan and medical progress allowing immunodeficient individuals to survive, partially explains the increasing incidence of listeriosis. Moreover, L. monocytogenes is ubiquitous and can grow at temperatures as low as 0 degrees C. At this temperature growth is very slow. The expansion of the agro-food industry, the widespread use of systems of cold storage and changes in consumers demands have led to a large increase in the pool of Listeria that can cause foodborne infections.

[Microbiological quality of street-vendor ice cream in Dakar]. / Qualité microbiologique des glaces vendues sur la voie publique à Dakar.

During a multicenter study initiated by the International Network of Pasteur Institutes and Associated Institutes, microbiological quality of street-vended ice creams in Dakar was evaluated. 313 samples of ice creams from 170 street-vendors were collected and tested for common foodborne pathogens and indicator organisms. Results showed that microbiological quality of 45% of tested samples was unsatisfactory because of large populations of aerobic mesophilic organisms (36.7%), thermotolerant coliforms bacteria (21.4%) and sometimes E. coli. (10.6%). Strict pathogens as Salmonella, Shigella and Vibrio cholerae were not found. An investigation conducted among vendors showed a lack of education and training; these vendors need information about food preparation and storage practices that reduce microbiological contamination of foods.

Evaluation of an rDNA Listeria probe for Listeria monocytogenes typing.

A Listeria monocytogenes DNA fragment, identified as part of the 23S rRNA gene and called B17, was used to type 266 L. monocytogenes strains and 43 strains of other Listeria species. Results were compared with those obtained: i) with pBA2 (which consists of a 2.3 kb Bacillus subtilis DNA fragment encoding 16S rRNA, inserted into the HindIII site of pBR322), a probe previously used for Listeria and L. monocytogenes ribotyping, and ii) with DNA macrorestriction profiles analysis. Twenty profiles were identified for L. monocytogenes using pB 17, three of which accounted for 87% of strains. This new rDNA probe had greater discriminatory power for serogroups 1/2 or 3 strains than for serogroup 4 strains. The number of varieties and the discrimination index were higher with this new probe than with pBA2, but DNA macrorestriction patterns analysis gave better discrimination between strains.

Listeria monocytogenes subtypes associated with mortality among fallow deer (Dama dama).

Different subtypes of Listeria monocytogenes were isolated from various animal and environmental samples during an episode of increased mortality on a fallow deer (Dama dama) farm. During a 4-wk period, six fallow deer died, including four does, one fawn, and one adult buck. Prior to death, one of the does had exhibited central nervous system signs characteristic of listeriosis. Postmortem examination of the six deer showed no histologic changes typical of listeriosis, although inflammatory changes were present in several organs. Different subtypes of L. monocytogenes were isolated from brain samples from six deer, from fodder and soil from the deer feeding area, and from faces of some healthy animals on the farm. Listeria monocytogenes, which was frequently isolated in the environment of the farm, was considered the probable major cause of mortality in these fallow deer.

Incidence of Listeria spp. in Breton live shellfish.

Live shellfish samples (120) were collected from nine littoral sites in Brittany (western France). They were screened for Listeria spp. and a count of faecal coliforms was carried out. Analysis of the results revealed Listeria spp. in 55% of samples, a much higher rate than the previous, infrequent, recorded data. Furthermore, the study demonstrated that the frequency of Listeria spp. in winter was more important than in summer (P < 0.001), and underlined a significant relationship between the occurrence of these bacteria and the concentration of faecal coliforms (P < 0.001). Finally, comparison of the official and Gen-Probe methods revealed the limits of the standardized technique in the search for L. monocytogenes in shellfish.

Listeriosis outbreak associated with the consumption of rillettes in France in 1993.

An outbreak of listeriosis involving 38 patients occurred in France between 18 June and 5 October 1993. The epidemic clone was characterized by serovar 4b, phagovar 2671:108:312, and DNA macrorestriction patterns 12 and 13. Thirty-one case-patients were materno-neonatal patients and 7 patients were nonpregnant adults. Preliminary analysis of a case-control study implicated a pork product, rillettes, of a particular brand (odds ratio, 18; 95% confidence interval, 2.2-208) as the vehicle of infection. Rillettes is a ready-to-eat food prepared with ham meat cooked with grease. The implicated lots of rillettes were recalled in mid-August, and the French authorities issued a warning to the general public. Microbiologic analysis of unopened plastic cans of rillettes confirmed the results of the case-control study 3 weeks after the recall. Final analysis showed that the rillettes was the major vehicle of the outbreak but suggested that other brand A meat products could also have been involved.

A fatal case of Listeria endocarditis in a man following his tending of goats suggests an epidemiological link which is not supported by the results.

A man died in endocarditis due to listeriosis in the late autumn. He had been looking after two goats during the summer. Listeria monocytogenas was isolated from a rectal swab from one of the goats. The goat faeces isolate and the human blood isolate were of identical serovar. The two isolates, however, were shown to be different by multilocus electrophoretic enzyme analysis and ribotyping, as well as by biotyping. Thus, these results do not support the hypothesis that the man was infected by the goat.

Foodborne listeriosis.

Various epidemiological investigations of outbreaks and sporadic cases have clearly demonstrated that the consumption of contaminated food is responsible for a high proportion of listeriosis cases and Listeria monocytogenes has been increasingly recognized as an important foodborne pathogen over the last 15 years. The emergence of listeriosis is the result of complex interactions of different factors: medical progress which increases the lifespan and allows immunodeficient people to survive, expansion of the food industry and cold storage systems as well as changes in food habits. None of these factors on its own is entirely responsible. Considerable research has attempted to characterize the organism, define the magnitude of the public health problem and its impact on the food industry, identify the risk factors associated with the disease, and devise appropriate control strategies. Nevertheless, a number of crucial questions remains incompletely elucidated (extent of the foodborne transmission of listeriosis, health status of apparently "healthy patients" with the possible role of an intercurrent infection or genetic susceptibility, how to distinguish highly virulent from less virulent strains of L. monocytogenes, factors contributing to the emergence of outbreaks, the possible role of healthy carriers in the epidemiology of listeriosis, etc.). To investigate the complexity of listeriosis requires the close collaboration of clinicians, epidemiologists, clinical and food microbiologists, food scientists and the food industry. A large amount of data has been accumulated during the past 10 years but more research is required to elucidate the epidemiology of the disease and the virulence of the causative agent.

A foodborne outbreak of gastroenteritis involving Listeria monocytogenes.

An outbreak of gastroenteritis occurred in Italy among 39 persons who had attended a private supper. All guests were previously healthy, young, non-pregnant adults; 18 (46%) had symptoms, mostly gastrointestinal (78%), with a short incubation period. Four were hospitalized with acute febrile gastroenteritis, two of whom had blood cultures positive for Listeria monocytogenes. No other microorganisms were recovered from the hospitalized patients' specimens. Epidemiological investigation identified rice salad as the most likely vehicle of the food-borne outbreak. L. monocytogenes was isolated from three leftover foods, the kitchen freezer and blender. Isolates from the patients, the foods and the freezer were indistinguishable: serotype 1/2b, same phage type and multilocus enzyme electrophoretic type. Eight (36%) of 22 guests tested were found to have antibodies against L. monocytogenes, compared with none of 11 controls from the general population. This point source outbreak was probably caused by infection with L. monocytogenes. Unusual features included the high attack rate among immunocompetent adults and the predominance of gastrointestinal symptoms.

[Taxonomy of the Listeria genus and typing of L. monocytogenes]. / Taxonomie du genre Listeria et typage de L. monocytogenes.

The genus Listeria contains six species (L. monocytogenes, L. innocua, L. ivanovii, L. seeligeri, L. welshimeri and L. grayi) among which only L. monocytogenes can cause infections in humans. Typing of L. monocytogenes includes phenotypic methods, serotyping and phage-typing, and molecular methods, mainly ribotyping, multilocus enzyme analysis, DNA micro- and macrorestriction analysis and RAPD (Random Amplified Polymorphic DNA).