In February 1999, an outbreak of listeriosis caused by Listeria monocytogenes serotype 3a occurred in Finland. All isolates were identical. The outbreak strain was first isolated in 1997 in dairy butter. This dairy began delivery to a tertiary care hospital (TCH) in June 1998. From June 1998 to April 1999, 25 case patients were identified (20 with sepsis, 4 with meningitis, and 1 with abscess; 6 patients died). Patients with the outbreak strain were more likely to have been admitted to the TCH than were patients with other strains of L. monocytogenes (60% vs. 8%; odds ratio, 17.3; 95% confidence interval, 2.8-136.8). Case patients admitted to the TCH had been hospitalized longer before cultures tested positive than had matched controls (median, 31 vs. 10 days; P=.008). An investigation found the outbreak strain in packaged butter served at the TCH and at the source dairy. Recall of the product ended the outbreak.
An outbreak of listeriosis in Sweden, consisting of nine cases, was investigated by means of molecular typing of strains from patients and strains isolated from suspected foodstuffs, together with interviews of the patients. Listeria monocytogenes was isolated from six of the patients, and all isolates were of the same clonal type. This clonal type was also isolated from a "gravad" rainbow trout, made by producer Y, found in the refrigerator of one of the patients. Unopened packages obtained from producer Y were also found to contain the same clonal type of L. monocytogenes. Based on the interview results and the bacteriological typing, we suspect that at least six of the nine cases were caused by gravad or cold-smoked rainbow trout made by producer Y. To our knowledge, this is the first rainbow trout-borne outbreak of listeriosis ever reported.
Serious infection with the bacterium L. monocytogenes mainly manifests as sepsis and/or meningitis. A particular entity is Listeria brain stem encephalitis, which is characterized by progressive brain stem deficits. The condition is fatal unless early treated. The purpose of the present study was to assess the incidence of brain stem encephalitis in a population-based listeriosis material. Medical records from 212 of the 240 patients with serious listeriosis reported in Norway from 1977 to 2000, as well as autopsy material from 8 of these patients, were available. This material was searched for clinical and neuropathological evidence of brain stem infection. Findings indicating brain stem encephalitis were present in 19 of the 172 patients with adult listeriosis (11%) but none of the 40 pregnancy-related listeriosis cases. None of the 19 patients had been diagnosed with Listeria brain stem infection originally. We conclude that brain stem encephalitis is relatively common in this Norwegian listeriosis material.
A 70-year-old woman fell seriously ill overnight with meningitis and was admitted to hospital. Cerebrospinal fluid culture yielded Listeria monocytogenes. One of the first problems in solving a human case of listeriosis suspected to be foodborne is to find the foods likely to have been transmitting L. monocytogenes. Two enrichment procedures and a direct plating procedure were used for isolation of the bacteria from different food items collected from the patient's refrigerator, local retail store and producer. Samples of vacuum-packed products of sliced pork brawn, sliced cooked medwurst and berliner wurst of the same brand harboured L. monocytogenes. Serotyping and restriction enzyme analysis (REA) with pulsed-field gel electrophoresis (PFGE) were used to characterize and compare 41 isolates, including the human strain. At least three clones were present in the foods investigated, and one of these was identical to the human clone. This clone was present in samples of medwurst from the patient's refrigerator and the local retail store. This is, to our knowledge, the first proven foodborne case of listeriosis reported in Sweden.
Public health authorities place a high priority on investigating listeriosis outbreaks, and these epidemiological investigations remain challenging. Some approaches have been described in the literature to address these challenges. This review of listeriosis clusters and outbreaks investigated in the Province of Quebec (Quebec) highlights investigative approaches that contributed to identifying the source of these outbreaks.
The Laboratoire de Santé Publique du Québec (LSPQ) implemented pulsed-field gel electrophoresis (PFGE) molecular subtyping in 1997 to identify Listeria monocytogenes clusters among isolates from invasive listeriosis cases identified throughout Quebec. A cluster was defined as three cases or more with the same or similar PFGE profiles (=3 band difference) occurring over a 4-month period. An investigation was initiated if the epidemiologic indicators suggested a common source. Listeriosis data from LSPQ's database were reviewed to identify and describe clusters detected from 1997 to 2011, including those that led to an outbreak investigation. Epidemiological reports prepared following each outbreak were also reviewed.
Eleven clusters were identified in the province by LSPQ between 1997 and 2011. Outbreak investigations were initiated for six clusters, four of which involved more than 10 cases. Factors that contributed to identifying the source for three of these outbreaks highlighted the value of (1) making all stakeholders (food safety and inspection services, public health authorities, and laboratories) aware of any ongoing investigation and sharing relevant information even if the source is not yet identified; (2) promptly collecting food samples identified and considered as possible vehicles of infection identified during the interview of a Listeria case; (3) collecting food items and/or environmental samples in locations reported in common by cases in the same cluster.
Multiple approaches should be considered when investigating L. monocytogenes clusters. Networks to facilitate continuous exchange of human and food data between public health and food safety partners should be encouraged.
In 1958-74 altogether 64 cases of bacteriologically verified infections of Listeria monocytogenes were diagnosed in Sweden in children, aged more than 27 days, and in adults. Immunosuppression predisposed to the disease. Thus, many patients had co-existing disorders, such as leukemia and alcoholism. Sixteen patients had been treated with corticosteroids, which were combined with cytostatic drugs in nine. Meningoencephalitis was diagnosed in 52 patients and was fatal in 16. The clinical symptoms did not differ from those in purulent meningitis caused by other bacteria. In the cerebrospinal fluid the cellular response was dominated by polymorphonuclear cells in 29 patients and by mononuclear cells in 20. Ten patients had septicemia, which was fatal in four. Clinical symptoms were dominated by chills, high fever and general prostration. One patient had pleurisy and one an abscess of the neck; both recovered. Serotypes 1 and 4b prevailed and were equally common. Many patients developed raised antibody titers in both the O-agglutination test and the complement fixation test. The titers were often not positive until after a month. Moderate granulocytosis was the rule and monocytosis was rarely seen. Ampicillin alone or combined with an aminoglycoside seemed to be the drug of choice in the treatment of listeriosis. An alternative drug was tetracycline. Most deaths occurred within six days of onset of the illness. Early diagnosis and treatment were imperative. Most patients recovered and serious sequelae were rare.
An outbreak of febrile gastroenteritis affected consumers of on-farm manufactured dairy products from a summer farm in Sweden. Symptoms included diarrhoea, fever, stomach cramps and vomiting in 88, 60, 54 and 21% of cases identified. The median incubation period was 31 h. A cohort study with 33 consumers showed an attack rate of 52% and an association between the total amount of product eaten and illness (P=0.07). Twenty-seven of 32 (84%) stool samples cultured for Listeria monocytogenes tested positive, although there was no association between clinical disease and the isolation of L. monocytogenes. In addition, gene sequences for VTEC and ETEC were detected in 6 and 1 subjects, respectively. Bacteriological analysis of cheese samples revealed heavy contamination with L. monocytogenes and coagulase positive staphylococci in all of them and gene markers for VTEC in one of them. Molecular profiles for L. monocytogenes isolated from dairy products, stool samples and an abscess from 1 patient who developed septic arthritis were identical. Results of both microbiological and epidemiological analyses point to L. monocytogenes as the most likely cause of this outbreak. The finding of markers for VTEC in some humans and cheese samples means that a mixed aetiology at least in some cases cannot be conclusively ruled out.
Isolates of Listeria monocytogenes (n = 932) isolated in Sweden during 1958-2010 from human patients with invasive listeriosis were characterized by serotyping and pulsed-field gel electrophoresis (PFGE) (AscI). Of the 932 isolates, 183 different PFGE types were identified, of which 83 were each represented by only one isolate. In all, 483 serovar 1/2a isolates were distributed over 114 PFGE types; 90 serovar 1/2b isolates gave 32 PFGE types; 21 serovar 1/2c isolates gave nine PFGE types; three serovar 3b isolates gave one PFGE type; and, 335 serovar 4b isolates gave 31 PFGE types. During the 1980s in Sweden, several serovar 4b cases were associated with the consumption of European raw soft cheese. However, as cheese-production hygiene has improved, the number of 4b cases has decreased. Since 1996, serovar 1/2a has been the dominant L. monocytogenes serovar in human listeriosis in Sweden. Therefore, based on current serovars and PFGE types, an association between human cases of listeriosis and the consumption of vacuum-packed gravad and cold-smoked salmon is suggested.