Listeriosis Outbreaks and Associated Food Vehicles, United States, 1998–2008

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Release date: December 12, 2012; Expiration date: December 12, 2013

Learning Objectives

Upon completion of this activity, participants will be able to:
• Assess the general epidemiology of listeriosis
• Analyze the epidemiology of listeriosis in the United States between 1998 and 2008
• Distinguish the most common food vehicle for listeriosis during the study period
• Evaluate clinical outcomes of listeriosis

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Thomas J. Gryczan, MS, Technical Writer/Editor, Emerging Infectious Diseases. Disclosure: Thomas J. Gryczan, MS, has disclosed no relevant financial relationships.

CME Author

Charles P. Vega, MD, Health Sciences Clinical Professor; Residency Director, Department of Family Medicine, University of California, Irvine. Disclosure: Charles P. Vega, MD, has disclosed no relevant financial relationships.

Authors

Disclosures: Emily J. Cartwright, MD; Kelly A. Jackson, MPH; Shacara D. Johnson, MSPH; Lewis M. Graves; Benjamin J. Silk, PhD, MPH; and Barbara E. Mahon, MD, MPH, have disclosed no relevant financial relationships.

Table of Contents
Volume 19, Number 1–January 2013

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Listeriosis Outbreaks and Associated Food Vehicles, United States, 1998–2008 - - Emerging Infectious Disease journal - CDC

Listeriosis Outbreaks and Associated Food Vehicles, United States, 1998–2008

Emily J. Cartwright, Kelly A. Jackson, Shacara D. Johnson, Lewis M. Graves, Benjamin J. Silk

, and Barbara E. Mahon

Author affiliations: Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Abstract

Listeria monocytogenes, a bacterial foodborne pathogen, can cause meningitis, bacteremia, and complications during pregnancy. This report summarizes listeriosis outbreaks reported to the Foodborne Disease Outbreak Surveillance System of the Centers for Disease Control and Prevention during 1998–2008. The study period includes the advent of PulseNet (a national molecular subtyping network for outbreak detection) in 1998 and the Listeria Initiative (enhanced surveillance for outbreak investigation) in 2004. Twenty-four confirmed listeriosis outbreaks were reported during 1998–2008, resulting in 359 illnesses, 215 hospitalizations, and 38 deaths. Outbreaks earlier in the study period were generally larger and longer. Serotype 4b caused the largest number of outbreaks and outbreak-associated cases. Ready-to-eat meats caused more early outbreaks, and novel vehicles (i.e., sprouts, taco/nacho salad) were associated with outbreaks later in the study period. These changes may reflect the effect of PulseNet and the Listeria Initiative and regulatory initiatives designed to prevent contamination in ready-to-eat meat and poultry products.

Listeria monocytogenes is transmitted predominantly through contaminated food (1). Listeriosis includes a spectrum of clinical illnesses ranging from febrile gastroenteritis to potentially fatal bacteremia and meningitis in groups at higher risk for invasive disease, including older adults and persons with certain medical conditions (2,3). Although pregnant women infected with L. monocytogenes typically experience a mild influenza-like illness or an asymptomatic infection, pregnancy-associated listeriosis can result in fetal loss, preterm delivery, invasive neonatal infection, and infant death.
The Centers for Disease Control and Prevention (CDC) estimates that 1,662 invasive infections with L. monocytogenes occur annually in the United States, causing 1,520 hospitalizations and 266 related deaths (4). Population-based surveillance demonstrated a 24% decrease in the crude incidence of laboratory-confirmed listeriosis from 0.41 to 0.31 cases per 100,000 population during 1996–2003 (5). Since 2003, the incidence of listeriosis has remained stable, with rates ranging from 0.25 to 0.32 cases per 100,000 population during 2004–2009. The 6-year average rates of hospitalization and death were 0.26 hospital admissions and 0.05 deaths or fetal losses per 100,000, respectively (6). Millions of US dollars in health care expenditures and quality-adjusted life years are lost to invasive listeriosis annually (7).
Foodborne transmission of listeriosis was first recognized conclusively after an outbreak in Canada in 1981 that was associated with consumption of contaminated coleslaw (1). In the United States, the first recognized foodborne listeriosis outbreak occurred in 1983 and was associated with pasteurized milk (8). During 1983–1998, outbreaks of foodborne listeriosis associated with Mexican-style cheese (9) and shrimp (10) were subsequently documented; a single case was also attributed to turkey frankfurters (11).
PulseNet, the national molecular subtyping network for enteric bacterial disease surveillance, was established in 1998 (www.cdc.gov/pulsenet). L. monocytogenes isolates from patients are sent to state public health laboratories for standardized pulsed-field gel electrophoresis (PFGE); the PFGE patterns are then uploaded to a central database (PulseNet) for national comparisons (12). When >2 L. monocytogenes isolates with indistinguishable PFGE pattern combinations are uploaded within a 120-day period, this cluster is evaluated. An investigation is initiated if the upload rate for this pattern combination is greater than the historical background or if other epidemiologic indicators suggest a common source.
Invasive listeriosis has been a nationally notifiable disease in the United States since 2001. Although most listeriosis cases are sporadic (i.e., not associated with a recognized cluster of illness), the detection of a listeriosis outbreak is a critical opportunity to prevent additional illness and death by removing a contaminated vehicle from the food supply. In addition, outbreak investigations often provide information about transmission of L. monocytogenes that can be used to improve food safety (13). However, epidemiologic investigations of listeriosis clusters are challenging because they are typically detected as a small number of geographically dispersed case-patients (some of whom may have died), and the incubation period can be lengthy, making patients’ recall of food exposures difficult (14).
Following a 2003 Council of State and Territorial Epidemiologists position statement, the Listeria Initiative was launched in 2004 to address these concerns (www.cdc.gov/listeria/surveillance.html). The Listeria Initiative encourages state and local health department officials to routinely interview all patients with culture-confirmed listeriosis as soon as they are reported by using a standardized, extended questionnaire to collect food histories. Concurrently, clinical isolates are submitted to public health laboratories for PFGE subtyping and submission to PulseNet, and PFGE results are linked to epidemiologic information in the Listeria Initiative database. When a cluster is identified in PulseNet, Listeria Initiative data related to that cluster can be reviewed quickly to identify common food exposures. The Listeria Initiative also facilitates case–case studies by comparing exposures reported by cluster-associated cases with information from listeriosis cases that are not associated with the cluster. The effectiveness of the case–case approach has been illustrated repeatedly, for example, during the investigation of large, multistate outbreaks associated with delicatessen turkey meat and cantaloupe (15,16).
This report summarizes single-state and multistate listeriosis outbreaks reported to CDC during 1998–2008. We describe characteristics of the outbreaks and affected patients to summarize outbreak trends, L. monocytogenes serotype distribution, and implicated foods.
Listeriosis Outbreaks and Associated Food Vehicles, United States, 1998–2008 - - Emerging Infectious Disease journal - CDC