Assessing the Use of PCR To Screen for Shedding of Salmonella enterica in Infected Humans

High-resolution serotyping reveals Salmonella surveillance challenges in the turkey industry

Despite extensive Salmonella controls used at processing, 5.5% of salmonellosis cases are linked to turkey. This study had two objectives: i) to summarize USDA-FSIS turkey Salmonella verification program data and ii) to evaluate Salmonella through turkey production and processing of 22 flocks. In objective 1, USDA-FSIS data shows the average Salmonella prevalence in ground turkey from 2016-2022 was 15.9%, and that the leading serovar changes frequently. For objective 2, bootsocks (n=22) were collected on-farm right after load-out. At processing, pre-scald wingtips (n=6 composites of 10/flock), pre-chill wingtips (n=6 composites of 10/flock), mechanically separated turkey (MST; n=6 bins/flock) and ground turkey (n=6 bins/flock) were collected. Salmonella prevalence was determined by a commercial qPCR and culture confirmed. In 33.2% of PCR-positive samples, Salmonella was not confirmed by culture, highlighting a discrepancy between molecular and culture detection. On-farm, 8/22 flocks were Salmonella positive, compared to 21 flocks that were positive at one or more processing locations, including 18 flocks that were positive in at least one final product sample. A logistic regression showed higher Salmonella prevalence in pre-scald (53.8%) than in pre-chill (18.2%), MST (27.3%) or ground turkey (26.5%). CRISPR-SeroSeq analysis of 148 culture positive samples detected 18 Salmonella serovars and showed 35.1% of samples contained multiple serovars. In 16 flocks, one or more serovars detected in final products were absent from any upstream samples. Two thirds of final product samples containing serovar Typhimurium typed as a live-attenuated Typhimurium vaccine strain. Salmonella on-farm and at pre-scald did not reflect Salmonella observed in final product. This data underscores the complexity of serovar tracking in turkey production and highlights challenges to identify surveillance samples that accurately represent Salmonella in turkey products.

Laboratory Criteria for Exclusion and Readmission of Potentially Infectious Persons in Sensitive Settings in the Age of Culture-Independent Diagnostic Tests: Report of a Multidisciplinary Workgroup

Culture-independent diagnostic tests (CIDTs) are increasingly used for clinical diagnosis of gastrointestinal diseases such as salmonellosis, Shiga toxin-producing E. coli disease, and shigellosis because of their speed, convenience, and generally high-performance characteristics. These tests are also used to screen potentially infectious asymptomatic persons during outbreak investigations in sensitive settings such as childcare, food service, and healthcare. However, only limited performance data are available for CIDTs used on specimens from asymptomatic persons. The Association of Public Health Laboratories (APHL) and Council of State and Territorial Epidemiologists (CSTE) convened a workgroup to examine the available scientific data to inform interim decision-making related to exclusion and readmission criteria for potentially infectious persons in sensitive settings, the risks and benefits of different testing strategies, and to identify knowledge gaps for further research. This is the report on the Workgroup findings.

Salmonella Subpopulations Identified from Human Specimens Express Heterogenous Phenotypes That Are Relevant to Clinical Diagnosis

Clonal bacterial cells can give rise to functionally heterogeneous subpopulations. This diversification is considered an adaptation strategy that has been demonstrated for several bacterial species, including Salmonella enterica serovar Typhimurium. In previous studies on mouse models infected orally with pure Salmonella cultures, derived bacterial cells collected from animal tissues were found to express heterogenous phenotypes. Here, we show mixed Salmonella populations, apparently derived from the same progenitor, present in human specimens collected at a single disease time point, and in a long-term-infected patient, these Salmonella were no longer expressing surface-exposed antigen epitopes by isolates collected at earlier days of the disease. The subpopulations express different phenotypes related to cell surface antigen expression, motility, biofilm formation, biochemical metabolism, and antibiotic resistance, which can all contribute to pathogenicity. Some of the phenotypes correlate with single nucleotide polymorphisms or other sequence changes in bacterial genomes. These genetic variations can alter synthesis of cell membrane-associated molecules such as lipopolysaccharides and lipoproteins, leading to changes in bacterial surface structure and function. This study demonstrates the limitation of Salmonella diagnostic methods that are based on a single-cell population which may not represent the heterogenous bacterial community in infected humans. IMPORTANCE In animal model systems, heterogenous Salmonella phenotypes were found previously to regulate bacterial infections. We describe in this communication that different Salmonella phenotypes also exist in infected humans at a single disease time point and that their phenotypic and molecular traits are associated with different aspects of pathogenicity. Notably, variation in genes encoding antibiotic resistance and two-component systems were observed from the subpopulations of a patient suffering from persistent salmonellosis. Therefore, clinical and public health interventions of the disease that are based on diagnosis of a single-cell population may miss other subpopulations that can cause residual human infections.

Salmonella Paratyphi B; Public Health and Parental Choice: When to Treat Asymptomatic Carriers of Infection?

BACKGROUND

Salmonella Paratyphi B (Paratyphoid B) is a rare infection and a notifiable disease in England. Disease is typically mild, and chronic carriage in children has been described in endemic countries. Almost all cases in England are imported, with very few cases of community transmission reported.

METHODS

The aim of this work was to describe an unusual cluster of Paratyphoid B cases transmitted within England, examining clinical, epidemiologic and microbiologic data. Detailed phylogenetic analysis is presented to corroborate public health epidemiologic links between cases.

RESULTS

One child had recently returned from an endemic area and had mild gastrointestinal symptoms. One year later, 2 other children with no travel history developed invasive disease requiring hospitalization. Epidemiologic links confirmed person-to-person spread between these three cases. All isolates of S. Paratyphi B (n = 93) received by the Gastrointestinal Bacteria Reference Unit between 2014 and 2019 were typed using whole genome sequencing. Three cases of Paratyphoid B were identified in the same geographical location over a 2-year period. S. Paratyphi B strains isolated from the stool and blood of the three cases were closely linked (0-5 single-nucleotide polymorphisms) using whole genome sequencing.

CONCLUSIONS

This case series highlights the potential public health risks of paratyphoid B and the range of pediatric complications associated with this illness, especially in younger children. Although rare, chronic carriage of Paratyphoid B can lead to transmission in nonendemic areas and should be considered in all children presenting with signs of enteric fever even where there is no history of foreign travel.