Surveillance of listeria infections in Europe

In addition to the economic consequences and threats associated with outbreaks, listeriosis remains of great public health concern, as it has one of the highest case fatality rates of all the foodborne infections (20%-30%), and has common source epidemic potential. Changes in the way food is produced, distributed and stored have created the potential for diffuse and widespread outbreaks involving many countries. In 2002, a survey was carried out to assess the need for and the feasibility of a European network on listeria infections in humans. Data on surveillance systems and laboratory methods were collected through two postal surveys sent to the national Centres for communicable disease surveillance and to the listeria reference laboratories. Surveillance systems for listeria infections were in operation in 16 out of the 17 countries surveyed, and 16 countries had a national reference laboratory (NRL). All countries based their case definition of listeriosis on the isolation of Listeria monocytogenes. Fourteen NRLs performed at least one typing method on human strains. At least 13 countries already carried out or expressed willingness to carry out characterisation of isolates by pulsed field gel electrophoresis (PFGE) of L. monocytogenes strains isolated from human cases following a standard protocol. The participants concluded that there was a clear added value to having a European surveillance network for listeria infections, particularly for outbreak detection and investigation, and that a surveillance network based on the existing national surveillance systems was feasible.

Foodborne Infections in France

To quantify the impact of foodborne diseases on health, and set priorities for data collection, prevention and control of these diseases, we compiled and analyzed information from surveillance systems and other sources on the morbidity and mortality due to foodborne infectious diseases in mainland France in the last decade of the 20th century. Illness due to 13 bacteria, two viruses, and eight parasites were studied. The number of foodborne infections, hospitalizations, and deaths were estimated from multiple data sources. For each agent, several estimates were derived from the different sources. Estimates were ranked according to their plausibility, based on an assessment of the validity of the data source, and are presented as a "plausible interval" consisting of a low and high estimate. We estimate that these pathogens caused 10,200-17,800 hospitalizations per year. Salmonella is the most frequent cause (5,700-10,200 cases), followed by Campylobacter (2,600-3,500 cases) and Listeria (304 cases). Toxoplasmosis accounts for the majority of hospitalizations (426 cases) attributable to the studied parasitic infections. The number of deaths related to foodborne infection was estimated between 228 and 691. Bacterial pathogens account for the majority (191 to 652) of deaths of which 92 to 535 are attributable to salmonellosis, ranking as the first cause of death, and 78 to listeriosis, the second cause. Salmonella, Campylobacter, and Listeria are the main causes of severe foodborne illness in France. For several pathogens, data are insufficient to derive exact estimates of the disease burden. Nevertheless, it has been possible to derive plausible estimates for the majority, and to rank them according to their impact on public health.

[Increase of Hantavirus infections in France, 2003]

BACKGROUND

Hantaviral infections causing hemorrhagic fever with renal syndrome are endemic in North Eastern France. Humans are contaminated by the inhalation of aerosols contaminated by rodent faeces. In February 2003, the National reference centre (NRC) for hemorrhagic fevers detected an increased number of cases. An investigation was carried out to confirm the outbreak and take appropriate control measures.

METHODS

Cases were collected by the NRC. A case was defined as a person living in France with symptoms compatible with hantaviral infection and a positive blood test both for specific Puumala IgM, and IgG. Clinical information and at-risk exposures during the 2 weeks before onset were recorded.

RESULTS

In 2003, 128 cases were diagnosed (61 in 2002). The median age of patients was 38, 77% were men and 82% were hospitalized. Patients were living in North-Eastern France. Clusters were detected in the Ardennes and Oise districts. Occupation (35%) (in agriculture, forestry, and construction work), manipulation of firewood (35%), gardening (29%), and outdoors leisure (14%) were identified as at-risk exposures in these cases.

CONCLUSIONS

An increased number of positive diagnoses of hantaviral infections was confirmed. The location and at-risk exposures of the cases were identical in previous investigations. Exclusion and prevention of rodents' access to houses and avoiding the inhalation of contaminated dust are the only possible prevention measures of hantaviral infections. Information about the disease and its prevention needs to be made widely available to both healthcare professionals and the general population living in endemic areas.

An outbreak of multidrug-resistant Salmonella enterica serotype Newport infections linked to the consumption of imported horse meat in France

In 2003, 14 cases of multidrug-resistant Salmonella Newport infections were reported. This is the first documented foodborne outbreak of multidrug-resistant S. Newport in France. The blaCMY gene was present in all isolates. All cases reported having eaten horse meat from a common wholesaler. The country of origin of the imported meat could not be identified.

Norovirus foodborne outbreaks associated with the consumption of oysters from the Etang de Thau, France, December 2002

In January 2003, the Institut de Veille Sanitaire received notification of clusters of gastroenteritis (GE) thought to be associated with consumption of oysters harvested from Etang de Thau in the south of France. At the same time Italy reported an outbreak (200+ cases) associated with oysters from the Etang de Thau. An investigation was carried out to determine the source and vehicle of the outbreaks. Descriptive analysis of reported clusters in France, microbiological analysis of stool and oyster samples, genotyping of noroviruses and an environmental investigation of the Etang de Thau were carried out. A retrospective cohort study was also undertaken among those attending a number of family meals in Paris. Thirteen family clusters in four districts of France (69 cases) could be attributed to the consumption of Thau oysters based on descriptive evidence. Oysters distributed at an office in Paris and consumed at fourteen family meals between 19 and 24 December led to a further outbreak. In this outbreak the attack rate was 21/36 (58%) for Thau oyster consumers and 0/22 for non-consumers (p=0.00002). Noroviruses (genogroups I and II) were found in stool samples from four clusters and oysters from three clusters (including Paris). Environmental investigations revealed heavy rainfall, an overflow of a water purification station and faecal contamination of the Etang de Thau in December. Oysters from the Etang de Thau were responsible for a number of clusters of norovirus GE in winter 2002 in France and also in Italy. High Escherichia Coli levels in Thau water and shellfish led to an official request, mid-December, for oyster purification before distribution. This was not possible, due to lack of purification facilities. This investigation has contributed to a change in the way that shellfish harvesting areas are classified in France.

Two outbreaks of Salmonella enteritidis phage type 8 linked to the consumption of Cantal cheese made with raw milk, France, 2001

Salmonelloses are one are the main causes of foodborne infections in industrialised countries. In France, the incidence of human salmonellosis recorded by the National Reference Centre for Salmonella and Shigella (CNRSS) in 2001 was 21 cases per 100,000 inhabitants, and Salmonella serotype Enteritidis represented 39% of cases (1). This article reports the investigation results of two community outbreaks of salmonellosis that occurred simultaneously in the south west of France, and which were linked to the consumption of cheese made from raw milk.

Creutzfeldt-Jakob disease and related diseases in France from 1998 to 2000

In France, the number of reports of suspected CJD increased from 1998 to 2000, probably due to the increase in the requests for biological tests: respectively 459 in 1998, 590 in 1999, and 823 in 2000. For all three years, the distribution by sex is similar, with a sex ratio (M/F) of 1.05. The proportion of suspected cases aged under 50 remained stable (16% of all reports in 1998–2000). The number of sporadic CJD, confirmed or probable, was stable, with a mortality ratio of 1.38 per one million in 1998, 1.56 in 1999, and 1.41 in 2000.

Creutzfeldt-Jakob disease and related diseases in France from 1998 to 2000

In France, the number of reports of suspected CJD increased from 1998 to 2000, probably due to the increase in the requests for biological tests: respectively 459 in 1998, 590 in 1999, and 823 in 2000. For all three years, the distribution by sex is similar, with a sex ratio (M/F) of 1.05. The proportion of suspected cases aged under 50 remained stable (16% of all reports in 1998-2000). The number of sporadic CJD, confirmed or probable, was stable, with a mortality ratio of 1.38 per one million in 1998, 1.56 in 1999, and 1.41 in 2000.

Clustered cases of leptospirosis in Rochefort, France, June 2001

Five clustered cases of leptospirosis were diagnosed in the area of Rochefort, France, in June 2001, among teenagers who had swum in the Genouillé canal. The symptoms included fever, headache, abdominal pain and vomiting, chills and myalgia. Three cases were confirmed by PCR and serology. The mean cumulative duration of bathing was significantly higher in cases (23.8 hours) compared to controls (14.4 hours). No other particular risk factor was observed. The environmental investigation revealed the presence of rodents excreting of leptospires near the bathing area. For all antigens considered, the occurence of seropositive rodents was 30.8%, L. icterohaemorrhagiae being the predominant serogroup (23,1%).

[The capture-recapture applied to epidemiology: principles, limits and application]

By matching several sources of information coming from the same population, the capture-recapture method allows, if matches between sources can be identified, to estimate the number of cases not identified by any of the sources, the total number (N) of cases in the population and the sensitivity of each source. Used first in zoology and demography, this technique has been increasingly applied to epidemiology in the last two decades. However, six conditions need to be satisfied: all cases identified by each source are true cases; occurred during the time and the geographical area studied; the study population is closed; all matches are true matches; sources are independent and there is no heterogeneous catchability within sources. It is possible to assess and take into account dependence between sources when 3 or more sources are used, in particular by log linear modelling. However interactions of maximal order cannot be adjusted for. In case of a biased estimation because of the non respect of the conditions, it is recommended to apply a method of correction. The complete application of the methods is illustrated in the study of estimating the number of Salmonella infectious foodborne outbreak. As capture-recapture studies often use data collected for other purposes, this technique should be regarded as exploratory or be used to validate an estimate of a number of cases obtained by another method. It should not replace population sampling methods only because of its low cost. Otherwise it is a very informative approach to evaluate the sensitivity and representativeness of surveillance systems and registries.

[Food-borne infections: do we need further data collection for public health action and research]

The data needed for controlling and preventing food-borne infectious diseases relied so far on surveillance of the main food-borne infections (Salmonella and listeria infections) to follow trends over time and detect outbreak. However, this systematic continuous data collection was not always sensitive enough to timely detect community outbreaks and did not take into account sporadic cases of food-borne infections which represent the majority of patients (such as Campylobacter infection for example). Therefore, the true burden of food-borne infections, including morbidity, mortality and the social and economic cost could not be assessed. As the issue of food-borne infections got more social attention, the need of further epidemiological data has increased including the implementation of large population studies (active surveillance and follow up studies) associated with analytical studies in the United States (Foodnet) and in some European countries (United Kingdom, The Netherlands, Denmark.). Meanwhile surveillance and detection of outbreaks have substantially improved through the use of new typing scheme, particularly those based on molecular techniques. Their routine use, now, allows an early identification of the clonal spread of food-borne bacteria. The application of automatic detection algorithm to surveillance data base has also improved the performance of outbreak detection and changes of trends. Furthermore, food-borne infection surveillance has become European which allows, by pooling of national database, to identify emergence that did not get noticed in any country. To foster the prevention of sporadic cases, the use of analytical epidemiology has become more and more frequent and has improved the knowledge of food vehicles and risk factors. The risk assessment approach has also been applied to the microbial contamination of food to answer to the increasing needs of expertise, particularly at the international level. This approach, however, needs further methodological development and the collection of extra information on the food chain. Last, but not the least, a wider public health research approach must also be considered, particularly on the social perception of food-borne risks and the cost-effectiveness analysis of the prevention measures that are taken.

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.

[Epidemiology of human Listeria infections in France]

Human listeriosis is a relatively rare but serious disease with case fatality rates between 20 and 30%. The majority of patients who have listeriosis present with meningitis or septicaemia. Listeriosis during pregnancy can lead to a congenital infection, neonatal sepsis and meningitis or foetal death. The main mode of transmission is through contaminated foods. The infection usually occurs sporadically but small outbreaks and even large epidemics have occurred in a large number of industrialised countries. During the last 10 years several Listeria monocytogenes control measures have been introduced and implemented at the retail level and in production for plants or foods potentially contaminated with Listeria monocytogenes. During this period the incidence of listeriosis decreased substantially and is at present estimated at 300-400 cases annually.

Minced beef and human salmonellosis: review of the investigation of three outbreaks in France

The synthesis of investigations of three salmonellosis outbreaks which occured in France between 1998 and 2000 confirms the role of the consumption of minced beef and highlights the importance of prevention measures.

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.

Risk factors for the occurrence of sporadic Salmonella enterica serotype typhimurium infections in children in France: a national case-control study

To determine risk factors for the occurrence of sporadic Salmonella typhimurium infections among children in France, we conducted a matched case-control study. Cases were identified between 15 June and 30 September 1996. We interviewed 101 pairs of case patients and control subjects, matched for age and place of residence. The risk of illness was greater for children who ate undercooked ground beef than for those who did not (odds ratio [OR], 5.0; 95% confidence interval [CI], 1.9-13.1). Case patients were more likely than control subjects to have taken antibiotics during the month before onset of disease (OR, 2.2; 95% CI, 1.0-4.9). Case patients <5 years of age were more likely to have been in contact with a household member with diarrhea 3-10 days before onset (P=.05). Consumption of undercooked ground beef is a risk factor for the sporadic occurrence of S. typhimurium infection among children, and antibiotics may facilitate the occurrence of illness. The possibility of person-to-person transmission among young children needs to be considered.

How many foodborne outbreaks of Salmonella infection occurred in France in 1995? Application of the capture-recapture method to three surveillance systems

Despite control measures, foodborne outbreaks of non-typhi Salmonella infection continue to occur in developed countries. The authors aimed to assess the number of foodborne Salmonella outbreaks that occurred in France in 1995 using a capture-recapture approach. Data from three sources--the National Public Health Network (NPHN), the Ministry of Agriculture (MA), which receives mandatory notification, and the National Salmonella and Shigella Reference Center (NRC)-were collected. Matching algorithms permitted identification of matched outbreaks. The total number of outbreaks was estimated by log-linear modeling taking into account source dependencies and the variable catchability. The final estimate was adjusted for the positive predictive value (66%) of the NRC case definition. The dependence between the NPHN and the MA was also evaluated by means of a qualitative survey. A total of 716 foodborne Salmonella outbreaks were reported to the three sources, and 108 matches were identified. The best-fitting model, taking into account a positive dependence between the NPHN and MA sources, gave an estimate of 757 outbreaks. The sensitivity was 15% for the NPHN, 10% for the MA, and 50% for the NRC. In France, routine mandatory reporting of foodborne Salmonella outbreaks is very incomplete, and it is not representative of the serotype and the type of outbreak.

Surveillance of haemolytic uraemic syndrome in children under 15 years of age in France in 1998

Data from a national network of paediatric nephrology departments in France suggest that the incidence of haemolytic uraemic syndrome (HUS) in 1998 was 0.7 cases per 100 000 children aged under 15 years and that cases occur sporadically. Six out of 85 cas

A community--wide outbreak of Salmonella enterica serotype Typhimurium infection associated with eating a raw milk soft cheese in France

In 1997, a community-wide outbreak of Salmonella enterica serotype Typhimurium (S. typhimurium) infection occurred in France. The investigation included case searching and a case-control study. A case was defined as a resident of the Jura district with fever or diarrhoea between 12 May and 8 July 1997, from whom S. typhimurium was isolated in stool or blood. One hundred and thirteen cases were identified. Thirty-three (83 %) of 40 cases but only 23 (55 %) of 42 community controls, matched for age and area of residence, reported eating Morbier cheese (Odds ratio: 6.5; 95 % Confidence Interval: 1.4-28.8). Morbier cheese samples taken from the refrigerators of two case-patients and one symptom-free neighbour cultured positive for S. typhimurium of the same phage type as the human isolates. The analysis of distribution channels incriminated one batch from a single processing plant. These findings show that an unpasteurized soft cheese is an effective vehicle of S. typhimurium transmission.

Outbreak of trichinellosis in the Midi-Pyrenees region of France January - March 1998

Two outbreaks of trichinellosis in the Tarn et Garonne, departement, France were reported by the departmental health autorities on 2 March 1998, to the Reseau National de Sante Publique (RNSP). An epidemiological investigation began on 3 March in order to

Outbreak of trichinellosis in the Midi-Pyrénées region of France January - March 1998

Two outbreaks of trichinellosis in the Tarn et Garonne, département, France were reported by the departmental health autorities on 2 March 1998, to the Réseau National de Santé Publique (RNSP). An epidemiological investigation began on 3 March in order to

Outbreak of Salmonella dublin infection in France, November - December 1995

On 20 December 1995, the National Network of Public Health (Reseau National de Sante Publique - RNSP) was notified by the Salmonella and Shigella National Reference Centre (Centre National de Reference - CNR) that a greater than expected number of human i