Microbiological Aspects of the Investigation That Traced the 1998 Outbreak of Listeriosis in the United States to Contaminated Hot Dogs and Establishment of Molecular Subtyping-Based Surveillance for Listeria monocytogenes in the PulseNet Network

Abstract

A multistate outbreak of listeriosis occurred in the United States in 1998 with illness onset dates between August and December. The outbreak caused illness in 108 persons residing in 24 states and caused 14 deaths and four miscarriages or stillbirths. This outbreak was detected by public health officials in Tennessee and New York who observed significant increases over expected listeriosis cases in their states. Subsequently, the Centers for Disease Control and Prevention (CDC) began laboratory characterization of clinical isolates of Listeria monocytogenes by serotyping and restriction fragment length polymorphism analysis using pulsed-field gel electrophoresis (PFGE). For the purpose of this investigation, outbreak-related isolates were defined as those that had a specific AscI-PFGE pattern and indistinguishable or highly similar (no more than 2 band difference in 26 bands) ApaI-PFGE patterns when their DNA was restricted by AscI and ApaI restriction enzymes. Timely availability of molecular subtyping results enabled epidemiologists to separate outbreak cases from temporally associated sporadic cases in the same geographic areas and facilitated the identification of contaminated hot dogs manufactured at a single commercial facility as the source of the outbreak. During the investigation of this outbreak, a standardized protocol for subtyping L. monocytogenes by PFGE was developed and disseminated to public health laboratories participating with CDC's PulseNet network; these laboratories were requested to begin routine PFGE subtyping of L. monocytogenes.

Characterization of Listeria monocytogenes Isolates from Human Listeriosis Cases in Italy

“…In our experience, overall, 11 clusters were identified among 54 human isolates from two different geographic areas of Italy based on serotyping and AscI pulsotypes and clustering confirmation by ApaI. In previous studies, AscI PFGE has provided evidence to accurately cluster epidemiologically related isolates and to separate isolates from different outbreaks, whereas the use of more-discriminatory ApaI PFGE as a primary approach led in some instances to inaccurate separation of epidemiologically related isolates (15). Consequently, a large proportion of the human listeriosis cases under investigation could be grouped into molecular subtype clusters, some of which could represent common-source outbreaks.…”

Detection of <i>Listeria monocytogenes</i> in Foods and Characterization by PFGE

“…They found to be recorded an outbreak of 16 cases caused by pre-sliced ready-to-eat (RTE) delicatessen meat (sausage salad) [24]. Moreover, evidence from EU-wide routine food safety investigations indicates that a substantial proportion of RTE products may be contaminated by L. monocytogenes [25]. The result also confirms RTE, meat, and fish are as one of the important enteropathogens responsible for listeriosis.…”

“…PFGE has been considered as a standard subtyping method for L. monocytogenes [19]. The PFGE method has a high discriminatory power and has been shown to be very accurate and reproducible for fine structure comparison and molecular typing of L. monocytogenes [20] [21].…”

Prophages in Listeria monocytogenes Contain Single-Nucleotide Polymorphisms That Differentiate Outbreak Clones within Epidemic Clones

“…However, their whole-genome macroarray strategy could not differentiate the 1998 outbreak isolates as a group from the 2002 outbreak isolates (9). Graves et al (6) and Kathariou (9) reported that ApaI PFGE could subgroup ECII isolates into four closely related clusters, with some clusters containing both the 1998 outbreak isolates and the 2002 outbreak isolates. In summary, isolates within each ECII outbreak had different genomic macroarray profiles and ApaI PFGE patterns; thus, the isolates within the same outbreak would be considered different strains according to the definition of strain given by the European Study Group on Epidemiological Markers (14).…”

“…In summary, isolates within each ECII outbreak had different genomic macroarray profiles and ApaI PFGE patterns; thus, the isolates within the same outbreak would be considered different strains according to the definition of strain given by the European Study Group on Epidemiological Markers (14). Therefore, we propose "outbreak clone" as a better term than the traditional term "outbreak strain" to describe different strains involved in the same outbreak (6). Previously, AscI PFGE was the only subtyping method that could distinguish the 1998 outbreak isolates as a group from the 2002 outbreak isolates (Fig.…”