ABSTRACT
We investigated an outbreak of listeriosis detected by whole-genome multilocus sequence typing and associated with packaged leafy green salads. Nineteen cases were identified in the United States during July 5, 2015-January 31, 2016; isolates from case-patients were closely related (median difference 3 alleles, range 0-16 alleles). Of 16 case-patients interviewed, all reported salad consumption. Of 9 case-patients who recalled brand information, all reported brands processed at a common US facility. The Public Health Agency of Canada simultaneously investigated 14 cases of listeriosis associated with this outbreak. Isolates from the processing facility, packaged leafy green salads, and 9 case-patients from Canada were closely related to US clinical isolates (median difference 3 alleles, range 0-16 alleles). This investigation led to a recall of packaged leafy green salads made at the processing facility. Additional research is needed to identify best practices and effective policies to reduce the likelihood of Listeria monocytogenes contamination of fresh produce.
Subject(s)
Disease Outbreaks , Food Microbiology , Foodborne Diseases/epidemiology , Foodborne Diseases/microbiology , Listeria , Listeriosis/epidemiology , Listeriosis/microbiology , Salads/microbiology , Adolescent , Adult , Aged , Aged, 80 and over , Canada/epidemiology , Child , Child, Preschool , Disease Notification , Female , Genome, Bacterial , Geography, Medical , Humans , Listeria/classification , Listeria/genetics , Listeria/isolation & purification , Listeriosis/transmission , Male , Middle Aged , Multilocus Sequence Typing , Pregnancy , Public Health Surveillance , Seasons , United States/epidemiology , Young AdultABSTRACT
Three multistate outbreaks between 2014 and 2016, involving case patients in and outside the United States, were linked to stone fruit, caramel apples, and packaged leafy green salad contaminated with Listeria monocytogenes singleton sequence type 382 (ST382), a serotype IVb-v1 clone with limited genomic divergence. Isolates from these outbreaks and other ST382 isolates not associated with these outbreaks were analyzed by whole-genome sequencing (WGS) analysis. The primary differences among ST382 strains were single nucleotide polymorphisms (SNPs). WGS analysis differentiated ST382 from a clonal complex 1 outbreak strain co-contaminating the caramel apples. WGS clustered food, environmental, and clinical isolates within each outbreak, and also differentiated among the three outbreak strains and epidemiologically unrelated ST382 isolates, which were indistinguishable by pulsed-field gel electrophoresis. ST382 appeared to be an emerging clone that began to diverge from its ancestor approximately 32 years before 2016. We estimated that there was 1.29 nucleotide substitution per genome (2.94 Mbp) per year for this clone.
Subject(s)
Disease Outbreaks , Food Microbiology , Foodborne Diseases/epidemiology , Genotype , Listeria monocytogenes/classification , Listeriosis/epidemiology , Multilocus Sequence Typing , Adolescent , Aged , Child , Child, Preschool , Cluster Analysis , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , Female , Foodborne Diseases/microbiology , Genome, Bacterial , Humans , Listeria monocytogenes/genetics , Listeria monocytogenes/isolation & purification , Listeriosis/microbiology , Male , Molecular Epidemiology , Polymorphism, Single Nucleotide , United StatesABSTRACT
In April 2016, PulseNet, the national molecular subtyping network for foodborne disease surveillance, detected a multistate cluster of Salmonella enterica serotype Oslo infections with an indistinguishable pulsed-field gel electrophoresis (PFGE) pattern (XbaI PFGE pattern OSLX01.0090).* This PFGE pattern was new in the database; no previous infections or outbreaks have been identified. CDC, state and local health and agriculture departments and laboratories, and the Food and Drug Administration (FDA) conducted epidemiologic, traceback, and laboratory investigations to identify the source of this outbreak. A total of 14 patients in eight states were identified, with illness onsets occurring during March 21-April 9, 2016. Whole genome sequencing, a highly discriminating subtyping method, was used to further characterize PFGE pattern OSLX01.0090 isolates. Epidemiologic evidence indicates Persian cucumbers as the source of Salmonella Oslo infections in this outbreak. This is the fourth identified multistate outbreak of salmonellosis associated with cucumbers since 2013. Further research is needed to understand the mechanism and factors that contribute to contamination of cucumbers during growth, harvesting, and processing to prevent future outbreaks.
Subject(s)
Cucumis sativus/microbiology , Disease Outbreaks , Salmonella Food Poisoning/epidemiology , Adolescent , Adult , Aged , Child , Child, Preschool , Female , Food Microbiology , Humans , Male , Middle Aged , Salmonella/isolation & purification , United States/epidemiology , Young AdultABSTRACT
In September 2015, PulseNet, the national molecular subtyping network for foodborne disease surveillance, identified a cluster of Listeria monocytogenes (Listeria) clinical isolates indistinguishable by two-enzyme pulsed-field gel electrophoresis (PFGE) pattern combination and highly related by whole-genome multilocus sequence typing (wgMLST). A case was defined as isolation of Listeria with the outbreak PFGE pattern and highly related by wgMLST with an isolation date on or after July 5, 2015, the isolate date of the earliest case in this cluster.
