Dianna Schoonmaker-Bopp

Multistate outbreak of listeriosis linked to Turkey deli meat and subsequent changes in US regulatory policy

BACKGROUNDnListeriosis, a life-threatening foodborne illness caused by Listeria monocytogenes, affects approximately 2500 Americans annually. Between July and October 2002, an uncommon strain of L. monocytogenes caused an outbreak of listeriosis in 9 states.nnnMETHODSnWe conducted case finding, a case-control study, and traceback and microbiological investigations to determine the extent and source of the outbreak and to propose control measures. Case patients were infected with the outbreak strain of L. monocytogenes between July and November 2002 in 9 states, and control patients were infected with different L. monocytogenes strains. Outcome measures included food exposure associated with outbreak strain infection and source of the implicated food.nnnRESULTSnFifty-four case patients were identified; 8 died, and 3 pregnant women had fetal deaths. The case-control study included 38 case patients and 53 control patients. Case patients consumed turkey deli meat much more frequently than did control patients (P = .008, by Wilcoxon rank-sum test). In the 4 weeks before illness, 55% of case patients had eaten deli turkey breast more than 1-2 times, compared with 28% of control patients (odds ratio, 4.5; 95% confidence interval, 1.3-17.1). Investigation of turkey deli meat eaten by case patients led to several turkey processing plants. The outbreak strain was found in the environment of 1 processing plant and in turkey products from a second. Together, the processing plants recalled > 30 million pounds of products. Following the outbreak, the US Department of Agricultures Food Safety and Inspection Service issued new regulations outlining a L. monocytogenes control and testing program for ready-to-eat meat and poultry processing plants.nnnCONCLUSIONSnTurkey deli meat was the source of a large multistate outbreak of listeriosis. Investigation of this outbreak helped guide policy changes designed to prevent future L. monocytogenes contamination of ready-to-eat meat and poultry products.

Pulsed-Field Gel Electrophoresis (PFGE) Analysis of Temporally Matched Listeria monocytogenes Isolates from Human Clinical Cases, Foods, Ruminant Farms, and Urban and Natural Environments Reveals Source-Associated as Well as Widely Distributed PFGE Types

ABSTRACT A total of 495 temporally and geographically matched Listeria monocytogenes isolates from human clinical cases, foods, ruminant farms, and urban and natural environments were used to investigate L. monocytogenes pulsed-field gel electrophoresis (PFGE) type diversity. Two-enzyme (AscI and ApaI) PFGE discriminated 310 PFGE types and exhibited higher overall discriminatory power (Simpsons index of discrimination [D] = 0.995) than either EcoRI ribotyping (D = 0.950) or AscI or ApaI single-enzyme PFGE (D = 0.992 for both). Seven PFGE types showed significant associations with specific sources, including one and four PFGE types, respectively, associated with human clinical cases and foods. Spatial analysis of 13 PFGE types occurring >5 times showed that two PFGE types were specific to a single processing facility each, where they appear to have persisted over time. Nine PFGE types were geographically widespread and occurred among isolates from multiple sources. For example, a PFGE type that matched isolates from listeriosis outbreaks in Los Angeles and Switzerland occurred among isolates from farms (n = 7), human clinical cases (n = 4), environmental sources (n = 3), and foods (n = 1). Our data indicate that (i) PFGE is highly discriminatory for the subtyping of L. monocytogenes, (ii) some L. monocytogenes PFGE types are associated with specific sources, and (iii) some L. monocytogenes PFGE types are widely distributed and appear to be stable and pandemic. Large PFGE type databases representing isolates from different sources are thus needed to appropriately interpret subtype data in epidemiological investigations and to identify common as well as source-specific PFGE types.

Multistate Outbreak of Pseudomonas fluorescens Bloodstream Infection after Exposure to Contaminated Heparinized Saline Flush Prepared by a Compounding Pharmacy

BACKGROUNDnPharmaceutical compounding, the manipulation of ingredients to create a customized medication, is a widespread practice. In January 2005, the Centers for Disease Control and Prevention was notified of 4 cases of Pseudomonas fluorescens bacteremia that were traced to contaminated heparinized saline intravenous flush syringes prepared as a compounded medical product.nnnPATIENTS AND METHODSnWe reviewed medical records of symptomatic patients with P. fluorescens-positive cultures of blood specimens or sections of explanted catheters, reviewed the production process of syringes, performed syringe cultures, compared isolates by pulsed-field gel electrophoresis (PFGE), and examined catheters by scanning electron microscopy.nnnRESULTSnWe identified 80 patients in 6 states with P. fluorescens-positive cultures during December 2004-March 2006. Sixty-four patients (80%) had received a diagnosis of cancer. Seventy-four (99%) of 75 patients for whom information about catheter type was available had long-term indwelling catheters. Thirty-three (41%) of 80 cases were diagnosed 84-421 days after the patients last potential exposure to a contaminated flush (delayed-onset cases). Compared with patients with early infection onset, more patients with delayed infection onset had venous ports (100% versus 50%; P <.001). By PFGE, clinical isolates from 50 (98%) of 51 patients were related to isolates cultured from unopened syringes. Scanning electron microscopy of explanted catheters revealed biofilms containing organisms morphologically consistent with P. fluorescens.nnnCONCLUSIONnThis outbreak underscores important challenges in ensuring the safety of compounded pharmaceuticals and demonstrates the potential for substantially delayed infections after exposures to contaminated infusates. Exposures to compounded products should be considered when investigating outbreaks. Patients exposed to contaminated infusates require careful follow-up, because infections can occur long after exposure.

A Whole-Genome Single Nucleotide Polymorphism-Based Approach To Trace and Identify Outbreaks Linked to a Common Salmonella enterica subsp. enterica Serovar Montevideo Pulsed-Field Gel Electrophoresis Type

ABSTRACT In this study, we report a whole-genome single nucleotide polymorphism (SNP)-based evolutionary approach to study the epidemiology of a multistate outbreak of Salmonella enterica subsp. enterica serovar Montevideo. This outbreak included 272 cases that occurred in 44 states between July 2009 and April 2010. A case-control study linked the consumption of salami made with contaminated black and red pepper to the outbreak. We sequenced, on the SOLiD System, 47 isolates with XbaI PFGE pattern JIXX01.0011, a common pulsed-field gel electrophoresis (PFGE) pattern associated with isolates from the outbreak. These isolates represented 20 isolates collected from human sources during the period of the outbreak and 27 control isolates collected from human, food, animal, and environmental sources before the outbreak. Based on 253 high-confidence SNPs, we were able to reconstruct a tip-dated molecular clock phylogeny of the isolates and to assign four human isolates to the actual outbreak. We developed an SNP typing assay to rapidly discriminate between outbreak-related cases and non-outbreak-related cases and tested this assay on an extended panel of 112 isolates. These results suggest that only a very small percentage of the human isolates with the outbreak PFGE pattern and obtained during the outbreak period could be attributed to the actual pepper-related outbreak (20%), while the majority (80%) of the putative cases represented background cases. This study demonstrates that next-generation-based SNP typing provides the resolution and accuracy needed for outbreak investigations of food-borne pathogens that cannot be distinguished by currently used subtyping methods.

Tracing Origins of the Salmonella Bareilly Strain Causing a Food-borne Outbreak in the United States.

BACKGROUNDnUsing a novel combination of whole-genome sequencing (WGS) analysis and geographic metadata, we traced the origins of Salmonella Bareilly isolates collected in 2012 during a widespread food-borne outbreak in the United States associated with scraped tuna imported from India.nnnMETHODSnUsing next-generation sequencing, we sequenced the complete genome of 100 Salmonella Bareilly isolates obtained from patients who consumed contaminated product, from natural sources, and from unrelated historically and geographically disparate foods. Pathogen genomes were linked to geography by projecting the phylogeny on a virtual globe and produced a transmission network.nnnRESULTSnPhylogenetic analysis of WGS data revealed a common origin for outbreak strains, indicating that patients in Maryland and New York were infected from sources originating at a facility in India.nnnCONCLUSIONSnThese data represent the first report fully integrating WGS analysis with geographic mapping and a novel use of transmission networks. Results showed that WGS vastly improves our ability to delimit the scope and source of bacterial food-borne contamination events. Furthermore, these findings reinforce the extraordinary utility that WGS brings to global outbreak investigation as a greatly enhanced approach to protecting the human food supply chain as well as public health in general.

A Large, Multiple-Restaurant Outbreak of Infection with Shigella flexneri Serotype 2a Traced to Tomatoes

BACKGROUNDnFoodborne outbreaks of Shigella infection are uncommon and tomatoes are an unusual vehicle. We describe a large, multiple-restaurant outbreak of Shigella flexneri serotype 2a infection that was associated with tomatoes.nnnMETHODSnWe conducted nationwide surveillance and a case-control study, collected fecal specimens for culture, and measured the survival of the outbreak strain of S. flexneri in tomatoes.nnnRESULTSnWe interviewed 306 of 886 ill restaurant patrons and 167 control subjects. Matched univariate analysis showed that several food items were associated with illness, but only tomatoes remained significant in multivariate models. Illness peaked at each restaurant within 24 h after the arrival of hand-sorted bruised and overripe tomatoes from a new distributor; all patient isolates that were tested were indistinguishable by PFGE. Sliced tomatoes from the distributor were inoculated with the outbreak strain, and viable S. flexneri were recovered for 72 h.nnnCONCLUSIONnTo prevent such outbreaks, persons with shigellosis should be excluded from handling food at all points along the distribution chain.

The prevalence of multidrug resistance is higher among bovine than human Salmonella enterica serotype Newport, Typhimurium, and 4,5,12:i:- isolates in the United States but differs by serotype and geographic region.

ABSTRACT Salmonella represents an important zoonotic pathogen worldwide, but the transmission dynamics between humans and animals as well as within animal populations are incompletely understood. We characterized Salmonella isolates from cattle and humans in two geographic regions of the United States, the Pacific Northwest and the Northeast, using three common subtyping methods (pulsed-field gel electrophoresis [PFGE], multilocus variable number of tandem repeat analysis [MLVA], and multilocus sequence typing [MLST]). In addition, we analyzed the distribution of antimicrobial resistance among human and cattle Salmonella isolates from the two study areas and characterized Salmonella persistence on individual dairy farms. For both Salmonella enterica subsp. enterica serotypes Newport and Typhimurium, we found multidrug resistance to be significantly associated with bovine origin of isolates, with the odds of multidrug resistance for Newport isolates from cattle approximately 18 times higher than for Newport isolates from humans. Isolates from the Northwest were significantly more likely to be multidrug resistant than those from the Northeast, and susceptible and resistant isolates appeared to represent distinct Salmonella subtypes. We detected evidence for strain diversification during Salmonella persistence on farms, which included changes in antimicrobial resistance as well as genetic changes manifested in PFGE and MLVA pattern shifts. While discriminatory power was serotype dependent, the combination of PFGE data with either MLVA or resistance typing data consistently allowed for improved subtype discrimination. Our results are consistent with the idea that cattle are an important reservoir of multidrug-resistant Salmonella infections in humans. In addition, the study provides evidence for the value of including antimicrobial resistance data in epidemiological investigations and highlights the benefits and potential problems of combining subtyping methods.

Neisseria wadsworthii sp. nov. and Neisseria shayeganii sp. nov., isolated from clinical specimens

An analysis of 16S rRNA gene sequences from archived clinical reference specimens has identified two novel Neisseria species. For each species, two strains from independent sources were identified. Amongst species with validly published names, the closest species to the newly identified organisms were Neisseria canis, N. dentiae, N. zoodegmatis, N. animaloris and N. weaveri. DNA-DNA hybridization studies demonstrated that the newly identified isolates represent species that are distinct from these nearest neighbours. Analysis of partial 23S rRNA gene sequences for the newly identified strains and their nearest neighbours provided additional support for the species designation. Bayesian analysis of 16S rRNA gene sequences suggested that the newly identified isolates belong to distinct but related species of the genus Neisseria, and are members of a clade that includes N. dentiae, N. bacilliformis and N. canis. The predominant cellular fatty acids [16u200a:u200a0, summed feature 3 (16u200a:u200a1ω7c and/or iso-15u200a:u200a0 2-OH) and 18u200a:u200a1ω7c], as well as biochemical and morphological analyses further support the designation of Neisseria wadsworthii sp. nov. (type strain 9715(T) =DSM 22247(T) =CIP 109934(T)) and Neisseria shayeganii sp. nov. (type strain 871(T) =DSM 22246(T) =CIP 109933(T)).

Enhanced Identification and Characterization of Non-O157 Shiga Toxin–Producing Escherichia coli: A Six-Year Study

Non-O157 Shiga toxin-producing Escherichia coli (STEC) are emerging pathogens with the potential to cause serious illness and impact public health due to diagnostic challenges. Between 2005 and 2010, the Wadsworth Center (WC), the public health laboratory of the New York State (NYS) Department of Health, requested that Shiga toxin enzyme immunoassay (EIA)-positive stool enrichment broths and/or stool specimens be submitted by clinical and commercial reference laboratories testing NYS patient specimens. A total of 798 EIA-positive specimens were received for confirmation and serotyping, and additionally a subset of STEC was assessed for the presence of six virulence genes (stx1, stx2, eaeA, hlyA, nleA, and nleB) by real-time polymerase chain reaction. We confirmed 591 specimens as STEC, 164 (28%) as O157 STEC, and 427 (72%) as non-O157 STEC. Of the non-O157 STEC serogroups identified, over 70% were O103, O26, O111, O45, O121, or O145. During this time period, WC identified and characterized a total of 1282 STEC received as E. coli isolates, stool specimens, or EIA broths. Overall, the STEC testing identified 59% as O157 STEC and 41% as non-O157 STEC; however, out of 600 isolates submitted to the WC as E. coli cultures, 543 (90%) were identified as O157 STEC. This report summarizes a 6-year study utilizing enhanced STEC testing that resulted in increased identification and characterization of non-O157 STEC in NYS. Continued utilization of enhanced STEC testing may lead to effective and timely outbreak response and improve monitoring of trends in STEC disease epidemiology.

Salmonella Cerro isolated over the past twenty years from various sources in the US represent a single predominant Pulsed-Field Gel Electrophoresis type

Salmonella Cerro prevalence in US dairy cattle has increased significantly during the past decade. Comparison of 237 Salmonella isolates collected from various human and animal sources between 1986 and 2009 using pulsed-field gel electrophoresis, antimicrobial resistance typing, and spvA screening, showed very limited genetic diversity, indicating clonality of this serotype. Improved subtyping methods are clearly needed to analyze the potential emergence of this serotype. Our results thus emphasize the critical importance of population-based pathogen surveillance for the detection and characterization of potentially emerging pathogens, and caution to critically evaluate the adequacy of diagnostic tests for a given study population and diagnostic application.