Salmonella enterica bacteraemia: a multi-national population-based cohort study

Trends in Enterobacterales Bloodstream Infections in Children

OBJECTIVES

Enterobacterales bloodstream infections (E-BSI) cause a significant burden of disease in children and are associated with antimicrobial resistance. We assessed temporal changes in the population-based incidence of E-BSI in children in Queensland, Australia.

METHODS

We conducted a cohort study of incidents of E-BSI occurring in children in Queensland between 2000 and 2019, with a total population of 19.7 million child years. Infections were linked to clinical outcomes in hospital admissions and vital statistics databases. We estimated age- and sex-standardized E-BSI incidence rates over time. Secondary outcomes included the proportion of extended-spectrum β-lactamase phenotypes per year, hospital length of stay, and mortality.

RESULTS

We identified 1980 E-BSI in 1795 children. The overall age- and sex-standardized incidence rate was 9.9 cases per 100 000 child years, which increased from 7.3 to 12.9 over the period studied, an increase of 3.9% (95% confidence interval: 3.1-4.7) per year. There were 3.6 cases of E. coli bloodstream infection per 100 000 child years, increasing annually by 4.7% (3.5-5.9). The Salmonella sp. bloodstream infection incidence was 3.0 cases per 100 000 child years, which increased from 2013 by 13.7% (3.8-24.3) per year. The proportion of extended-spectrum β-lactamase E. coli increased over time. Mortality and length of stay were higher among children with comorbidities than those without (4.0% vs 0.3%, and 14 vs 4 days, respectively, P < .001).

CONCLUSIONS

The age- and sex-standardized incidence of E-BSI almost doubled in Queensland children over 2 decades, driven by increases in Salmonella sp. and E. coli. Increasing resistance of E. coli should prompt the inclusion of children in antimicrobial clinical trials.

A Population-Based Study on the Incidence, Risk Factors, and Outcome of Salmonella Bloodstream Infections in South Sweden 2012-2022

INTRODUCTION

Invasive infections caused by Salmonella are a significant global health concern. This population-based study aimed to comprehensively analyze invasive Salmonella infections in South Sweden, focusing on incidence, clinical presentation, risk factors, and outcomes.

METHODS

This population-based observational cohort study, conducted from 2012 to 2022, included all patients with Salmonella bloodstream infections (BSI) in the Skåne region, South Sweden. A control group consisted of patients with positive stool cultures/PCR for Salmonella but without BSI. Data were collected following a predefined study protocol from medical records. Standardized statistical analyses assessed patient characteristics, clinical presentation, and outcomes.

RESULTS

Between 2012 and 2022, 149 patients with SBSI were identified, with the majority having non-typhoidal Salmonella (NTS) infections (95%). A declining trend in the incidence of SBSI was observed, with the highest incidence in 2012 (1.5 per 100,000 person-years) and the lowest in 2020 (0.3 per 100,000 person-years). Patients with BSI were more likely to be older, have comorbidities, be immunosuppressed, and use proton pump inhibitors (PPIs). Additionally, patients with BSI presented with fewer gastrointestinal symptoms, had a higher respiratory rate, lower saturation, and higher SOFA scores, suggesting a more septic presentation. Patients with SBSI had significantly longer hospital stays and higher 30-day, 90-day, 180-day, and 365-day mortality rates compared to the control group.

CONCLUSION

Invasive Salmonella infections are rare in South Sweden. In a cohort of enteric and invasive Salmonella infection, the absence of classic gastroenteritis symptoms increases the risk of Salmonella bloodstream infection. This study highlights the importance of distinguishing between clinical presentations to guide appropriate treatment when Salmonella infection is suspected. The declining trend in incidence, particularly associated with international travel, necessitates further investigation to understand contributing factors.

Diversity of Salmonella enterica phages isolated from chicken farms in Kenya

IMPORTANCE

Non-typhoidal Salmonella enterica infections are one of the leading causes of diarrhoeal diseases that spread to humans from animal sources such as poultry. Hence, keeping poultry farms free of Salmonella is essential for consumer safety and for a better yield of animal products. However, the emergence of antibiotic resistance due to over usage has sped up the search for alternative biocontrol methods such as the use of bacteriophages. Isolation and characterization of novel bacteriophages are key to adapt phage-based biocontrol applications. Here, we isolated and characterized Salmonella phages from samples collected at chicken farms and slaughterhouses in Kenya. The genomic characterization of these phage isolates revealed that they belong to four ICTV (International Committee on Taxonomy of Viruses) phage genera. All these phages are lytic and possibly suitable for biocontrol applications because no lysogenic genes or virulence factors were found in their genomes. Hence, we recommend further studies on these phages for their applications in Salmonella biocontrol.

Draft genome of clinical isolate Salmonella enterica Typhimurium ms204 from Odisha, India, reveals multi drug resistance and decreased virulent gene expression

Salmonellosis, a food-borne illnesses caused by enteropathogenic bacterium Salmonella spp., is a continuous concern in both developed and developing countries. This study was carried out to perform an in-depth examination of an MDR Salmonella strain isolated from gastroenteritis patients in Odisha, India, in order to understand the genomic architecture, distribution of pathogenic island regions, and virulence factor diversity. Fecal samples were obtained from individuals with acute gastroenteritis and further subjected to panel of biochemical tests. The IlluminaHiSeq X sequencer system was used to generate whole-genome sequencing. The draft genome was submitted to gene prediction and annotation using RAST annotation system. Pathogenicity Island database and bioinformatics pipeline were used to find Salmonella pathogenicity islands (SPI) from the built scaffold. The gene expression in SPI1 and SPI2 encoded regions was investigated using qRT-PCR. The taxonomic position of Salmonella enterica subsp. enterica serovar Typhimurium was validated by serotype analysis and 16S rRNA based phylogenetic analysis. The de-novo genome assembly showed total length of 5,034,110 bp and produced 37 contigs. There are nine prophage areas, comprising of 12 regions and scaffold 8 contained a single plasmid, IncFIB. The isolate contains six known SPI genes content which was shown to be largely conserved from SPI1 to SPI2. We identified the sit ABCD cluster regulatory cascade and acquired antibiotic resistance genes in S. enterica Typhimurium ms204. Further research may aid in the correct diagnosis and monitoring of MDR Salmonella strains with a variety of physiological activities.

The Prolonged Treatment of Salmonella enterica Strains with Human Serum Effects in Phenotype Related to Virulence

Salmonella enterica as common pathogens of humans and animals are good model organisms to conduct research on bacterial biology. Because these bacteria can multiply in both the external environments and in the living hosts, they prove their wide adaptability. It has been previously demonstrated that prolonged exposition of Salmonella serotype O48 cells to normal human serum led to an increase in resistance to sera in connection with the synthesis of very long O-antigen. In this work, we have studied the phenotype connected to virulence of Salmonella enterica strains that were subjected to consecutive passages in 50% human serum from platelet-poor plasma (SPPP). We found that eight passages in SPPP may not be enough for the bacteria to become serum-resistant (S. Typhimurium ATCC 14028, S. Senftenberg). Moreover, C1q and C3c complement components bound to Salmonellae (S. Typhimurium ATCC 14028, S. Hammonia) membrane proteins, which composition has been changed after passaging in sera. Interestingly, passages in SPPP generated genetic changes within gene fljB, which translated to cells’ motility (S. Typhimurium ATCC 14028, S. Erlangen). One strain, S. Hammonia exposed to a serum developed a multi-drug resistance (MDR) phenotype and two S. Isaszeg and S. Erlangen tolerance to disinfectants containing quaternary ammonium salts (QAS). Furthermore, colonial morphotypes of the serum adaptants were similar to those produced by starter cultures. These observations suggest that overcoming stressful conditions is manifested on many levels. Despite great phenotypic diversity occurring after prolonged exposition to SPPP, morphotypes of colonies remained unchanged in basic media. This work is an example in which stable morphotypes distinguished by altered virulence can be confusing during laboratory work with life-threatening strains.

Risk Factors and Outcomes of Bloodstream Infections Among People With Human Immunodeficiency Virus: A Longitudinal Cohort Study From 2000 to 2017

Background

Bloodstream infections (BSIs) among people with human immunodeficiency virus (PWH) remain a poorly studied source of morbidity and mortality. We characterize the epidemiology, microbiology, and clinical outcomes including reinfection, hospitalization, and mortality rates of both community-acquired and hospital-acquired BSI in PWH.

Methods

We identified all BSI, between January 1, 2000 and December 31, 2017 in PWH in care at Southern Alberta Clinic, by linking data from laboratory and clinical databases. Crude incidence rates per 1000 person-years for BSI and death were calculated. Cox proportional hazards models estimated crude and adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) to conduct a risk factor analysis of BSI in PWH. Logistic regression models with generalized estimating equations estimated crude and adjusted odds ratios (aORs) to identify characteristics associated with 1-year mortality after BSI.

Results

Among 2895 PWH, 396 BSI episodes occurred in 228 (8%) PWH. There were 278 (72%) Gram-positive and 109 (28%) Gram-negative BSI. People with human immunodeficiency virus with lower CD4 nadirs, higher Charlson comorbidity indices, and hepatitis C virus were at highest risk for BSI. Long-term all-cause mortality was greater in those experiencing BSI (HR, 5.25; 95% CI, 4.21-6.55). CD4 count <200 cells/mm³ measured closest to the time of BSI was associated with 1-year mortality after BSI (aOR, 3.88; 95% CI, 1.78-8.46). Repeat episodes (42%) and polymicrobial BSI (19%) were common.

Conclusions

Bloodstream infections continue to occur at an elevated rate among PWH with high reoccurrence rates and associated morbidity and mortality. To risk stratify and develop targeted interventions, we identified PWH at greatest risk for BSI. People with human immunodeficiency virus with low immunity at the time of BSI are at highest risk of poor outcomes.

Genome analysis and virulence gene expression profile of a multi drug resistant Salmonella enterica serovar Typhimurium ms202

Background

In India, multi-drug resistance in Salmonella enterica serovar Typhimurium poses a significant health threat. Indeed, S. Typhimurium has remained unknown for a large portion of its genome associated with various physiological functions including mechanism of drug resistance and virulence. The whole-genome sequence of a Salmonella strain obtained from feces of a patient with gastroenteritis in Odisha, India, was analyzed for understanding the disease association and underlying virulence mechanisms.

Results

The de novo assembly yielded 17 contigs and showed 99.9% similarity to S. enterica sub sp enterica strain LT2 and S. enteric subsp salamae strain DSM 9220. S. Typhimurium ms202 strain constitutes six known Salmonella pathogenicity islands and nine different phages. The comparative interpretation of pathogenic islands displayed the genes contained in SPI-1 and SPI-2 to be highly conserved. We identified sit ABCD cluster regulatory cascade in SPI-1. Multiple antimicrobial resistance genes were identified that directly implies antibiotic-resistant phenotype. Notably, seven unique genes were identified as "acquired antibiotic resistance". These data suggest that virulence in S. enterica Typhimurium ms202 is associated with SPI-1 and SPI-2. Further, we found several virulent genes encoding SPI regions belonging to type III secretion systems (T3SS) of bacteria were significantly upregulated in ms202 compared to control LT2. Moreover, all these genes were significantly downregulated in S. enterica Typhimurium ms202 as compared to control LT2 on adding Mn²⁺ exogenously.

Conclusions

Our study raises a vital concern about the potential diffusion of a novel multi-drug resistant S. enterica Typhimurium ms202. It justifies this clinical pathogen to demonstrate a higher degree survival due to higher expression of virulent genes and enhanced ability of metallic ion acquisition.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13099-022-00498-w.

Risk of non-typhoidal Salmonella infection in patients with cholecystectomy: Results from a nationwide matched cohort study in Taiwan

BACKGROUND

The current study was designed to investigate the association between cholecystectomy and the risk of non-typhoidal Salmonella (NTS) infection.

METHODS

We obtained claims-based data from the Taiwan National Health Insurance Research Database (NHIRD) to perform a nationwide cohort study. A propensity score (PS)-matching analysis was performed with a ratio of 1:2 in the cholecystectomy cohort and cholecystectomy-free group to reduce selection bias. Both groups were followed until NTS diagnosis, a dropout from the insurance programme or the end of 2013. Cox proportional hazard regression analysis was used to estimate the hazard ratio (HR) and 95% confidence interval (CI) for the risk of NTS infection between the cholecystectomy and cholecystectomy-free groups.

RESULTS

Our study enrolled 197 444 patients who had undergone cholecystectomy and 394 888 patients who did not receive cholecystectomy. The adjusted HR (aHR) of NTS infection was 1.34 (95% CI, 1.13-1.58; P < .001) for the cholecystectomy group after adjusting for demographical characteristics and relevant comorbidities. The study population is predominantly female patients (55%) and older (58% older than 50 years). The subgroup analysis revealed that both sexes and notably, patients aged >50, who underwent cholecystectomy had a higher risk of NTS infection than the matched controls. Follow-up of patients who underwent cholecystectomy showed that they had a significantly higher risk of NTS infection for more than 6 months after the procedure.

CONCLUSIONS

Our study showed that cholecystectomy might be an independent risk factor for subsequent NTS infection.

Targeting Salmonella Typhimurium Invasion and Intracellular Survival Using Pyrogallol

Salmonella enterica serovar Typhimurium, an intracellular pathogen, evades the host immune response mechanisms to cause gastroenteritis in animals and humans. After invading the host cells, the bacteria proliferate in Salmonella-containing vacuole (SCV) and escapes from antimicrobial therapy. Moreover, Salmonella Typhimurium develops resistance to various antimicrobials including, fluoroquinolones. Treating intracellular bacteria and combating drug resistance is essential to limit the infection rate. One way of overcoming these challenges is through combination therapy. In this study, Pyrogallol (PG), a polyphenol, is combined with marbofloxacin (MAR) to investigate its effect on Salmonella Typhimurium invasion and intracellular survival inhibition. The Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of PG against Salmonella Typhimurium were 128 and 256 μg/mL, respectively. The lowest fractional inhibitory concentration (FIC) index for a combination of PG and MAR was 0.5. The gentamycin protection assay revealed that PG (30 μg/mL) alone and in combination with sub-MIC of MAR inhibited 72.75 and 76.18% of the invading bacteria in Caco-2 cells, respectively. Besides, the intracellular survival of Salmonella Typhimurium was reduced by 7.69 and 74.36% in treatment with PG alone and combined with sub-MIC of MAR, respectively, which was visualized by the confocal microscopy. PG has also shown to increase the intracellular accumulation of fluoroquinolone by 15.2 and 34.9% at 30 and 100 μg/mL concentration, respectively. Quantitative real-time PCR demonstrated PG suppressed the genetic expression of hilA, invF, sipB, and acrA by 14.6, 15.4, 13.6, and 36%, respectively. However, the downregulation of hilA, invF, sipB, and acrA increased to 80, 74.6, 78, and 70.1%, in combination with sub-MIC of MAR, respectively. Similarly, PG combined with MAR inhibited the expression of sdiA, srgE, and rck genes by 78.6, 62.8, and 61.8%, respectively. In conclusion, PG has shown antimicrobial activity against Salmonella Typhimurium alone and in combination with MAR. It also inhibited invasion and intracellular survival of the bacteria through downregulation of quorum sensing, invading virulence, and efflux pump genes. Hence, PG could be a potential antimicrobial candidate which could limit the intracellular survival and replication of Salmonella Typhimurium.

Simultaneous disseminated infections with intracellular pathogens: an intriguing case report of adult-onset immunodeficiency with anti-interferon-gamma autoantibodies

Background

Severe and disseminated non-tuberculous mycobacterial (NTM) infections are frequently linked to a genetic predisposition but acquired defects of the interferon gamma (IFNγ) / interleukin 12 (IL-12) pathway need to be considered in adult patients with persistent or recurrent infections. Neutralizing anti-IFNγ autoantibodies disrupting IFNγ signalling have been identified as the cause of a severe and unique acquired immunodeficiency syndrome with increased susceptibility to NTM and other intracellular pathogens.

Case presentation

An adult Asian female with a previous history of recurrent NTM infections presented with persistent diarrhea, abdominal pain, night sweats and weight loss. Severe colitis due to a simultaneous infection with cytomegalovirus (CMV) and Salmonella typhimurium was diagnosed, with both pathogens also detectable in blood samples. Imaging studies further revealed thoracic as well as abdominal lymphadenopathy and a disseminated Mycobacterium intracellulare infection was diagnosed after a lymph node biopsy. Further diagnostics revealed the presence of high-titer neutralizing anti-IFNγ autoantibodies, allowing for the diagnosis of adult-onset immunodeficiency with anti-IFNγ autoantibodies (AIIA).

Conclusions

We here present a severe case of acquired immunodeficiency with anti-IFNγ autoantibodies with simultaneous, disseminated infections with both viral and microbial pathogens. The case illustrates how the diagnosis can cause considerable difficulties and is often delayed due to unusual presentations. Histological studies in our patient give further insight into the pathophysiological significance of impaired IFNγ signalling. B-cell-depleting therapy with rituximab offers a targeted treatment approach in AIIA.

Salmonella identified in pigs in Kenya and Malawi reveals the potential for zoonotic transmission in emerging pork markets

Salmonella is a major cause of foodborne disease globally. Pigs can carry and shed non-typhoidal Salmonella (NTS) asymptomatically, representing a significant reservoir for these pathogens. To investigate Salmonella carriage by African domestic pigs, faecal and mesenteric lymph node samples were taken at slaughter in Nairobi, Busia (Kenya) and Chikwawa (Malawi) between October 2016 and May 2017. Selective culture, antisera testing and whole genome sequencing were performed on samples from 647 pigs; the prevalence of NTS carriage was 12.7% in Busia, 9.1% in Nairobi and 24.6% in Chikwawa. Two isolates of S. Typhimurium ST313 were isolated, but were more closely related to ST313 isolates associated with gastroenteritis in the UK than bloodstream infection in Africa. The discovery of porcine NTS carriage in Kenya and Malawi reveals potential for zoonotic transmission of diarrhoeal strains to humans in these countries, but not for transmission of clades specifically associated with invasive NTS disease in Africa.

The Salmonella enterica serovar Typhimurium virulence factor STM3169 is a hexuronic acid binding protein component of a TRAP transporter

The intracellular pathogen S. Typhimurium is a leading cause of foodborne illness across the world and is known to rely on a range of virulence factors to colonize the human host and cause disease. The gene coding for one such factor, stm3169, was determined to be upregulated upon macrophage entry and its disruption reduces survival in the macrophage. In this study we characterize the STM3169 protein, which forms the substrate binding protein (SBP) of an uncharacterized tripartite ATP-independent periplasmic (TRAP) transporter. Genome context analysis of the genes encoding this system in related bacteria suggests a function in sugar acid transport. We demonstrate that purified STM3169 binds d-glucuronic acid with high affinity and specificity. S. Typhimurium LT2 can use this sugar acid as a sole carbon source and the genes for a probable catabolic pathway are present in the genome. As this gene was previously implicated in macrophage survival, it suggests a role for d-glucuronate as an important carbon source for S. Typhimurium in this environment.

Lumbar Salmonella osteomyelitis with psoas muscle abscess in a patient with prostate cancer

Salmonella osteomyelitis is a rare clinical entity more commonly described in grounds of sickle cell disease however some cases has been described in patients without this pathology but an immunocompromised state, which also predisposes to the development of a psoas abscess.

We present the case of a 77-year-old man with persistent hip pain and recent diagnosis of prostate cancer who developed lumbar osteomyelitis and a secondary psoas abscess due contiguous spread. Treatment included a third-generation cephalosporine and fluoroquinolone without surgical drainage with a good prognosis overall.

Bacteremia Caused by Salmonella Poona in a Healthy Adult in Tokyo, Japan

Non-typhoidal Salmonella (NTS) infection is a major pathogen causing gastroenteritis among immunocompetent adults. NTS infection is mainly transmitted by contaminated food and water, but some cases are transmitted by animal contact. Salmonella enterica subsp. enterica serovar Poona (S. Poona) is an NTS usually transmitted by reptiles, and cases including outbreaks of gastroenteritis have been reported previously. However, invasive infections due to this organism among immunocompetent adults are rare. We herein report a case of a 39-year-old man who was admitted to our hospital for a fever and headache. Blood cultures were positive for S. Poona, although he did not recall any exposure to reptiles. He was treated successfully with intravenous ceftriaxone without any subsequent complications. This case implies that NTS bacteremia can occur in immunocompetent adults, and the diagnosis may be challenging since there may be no clear exposure or focal physical signs.

Changing epidemiology of invasive non-typhoid Salmonella infection: a nationwide population-based registry study

OBJECTIVES

Non-typhoid Salmonella (NTS) may invade beyond the intestine, causing bacteraemia, sepsis, and infection of normally sterile sites. The epidemiology of invasive NTS (iNTS) infection is under-researched. We determined trends, risk factors, serotype distribution, antimicrobial resistance (AMR), and attributable sources of iNTS infection in a high-income setting.

METHODS

22,837 records of culture-confirmed human salmonellosis cases and 10,008 serotyped Salmonella isolates from five putative animal reservoirs (pigs, cattle, broilers, layers, reptiles) in the Netherlands during 2005-2018 were retrieved from national surveillance registries. Risk factors for iNTS infection were identified using logistic regression analysis. Source attribution modelling was based on serotyping, prevalence, and exposure data.

RESULTS

The average annual percentage of iNTS infections was 4.6% (range 3.5-5.7%). An increase in iNTS infections was observed since 2012 (odds ratio (OR) 1.09, 95% confidence interval (95% CI) 1.04-1.14). Increased iNTS infection risk was associated with wintertime (OR 1.37, 95% CI 1.12-1.66), male sex (OR 1.73, 95% CI 1.51-1.99), older age (ORs: 3.27 to 16.33, depending on age groups), and living in rural areas (OR 1.54, 95% CI 1.23-1.93). While 52% of iNTS infections (n = 950) were caused by serotypes Enteritidis and Typhimurium, those displaying the highest invasiveness relative to their occurrence were Dublin (32.9%, n = 163), Panama (21.6%, n = 106), and Poona (14.1%, n = 71). Cattle were a larger source of iNTS than non-iNTS infections (12.2% vs. 7.6%). Lower AMR and multi-resistance rates were observed among iNTS (37.9%) than non-iNTS isolates (48.6%).

DISCUSSION

The increase in iNTS infections, which is reported also in other countries, is of public health and clinical concern. The underlying reasons seem to be multi-factorial in nature. iNTS infection risk depends more on the infecting serotypes and patient demographics, and less on the attributable reservoirs and AMR profiles.

Genetic changes associated with the temporal shift in invasive non-typhoidal Salmonella serovars in Bamako Mali

BACKGROUND

Invasive non-typhoidal Salmonella (iNTS) serovars S. Typhimurium and S. Enteritidis are major etiologic agents of invasive bacterial disease among infants and young children in sub-Saharan Africa, including in Mali. Early studies of iNTS serovars in several countries indicated that S. Typhimurium was more prevalent than S. Enteritidis, including in Mali before 2008. We investigated genomic and associated phenotypic changes associated with an increase in the relative proportion of iNTS caused by S. Enteritidis versus S. Typhimurium in Bamako, Mali, during the period 2002-2012.

METHODOLOGY/PRINCIPAL FINDINGS

Comparative genomics studies identified homologs of tetracycline resistance and arsenic utilization genes that were associated with the temporal shift of serovars causing iNTS shift, along with several hypothetical proteins. These findings, validated through PCR screening and phenotypic assays, provide initial steps towards characterizing the genomic changes consequent to unknown evolutionary pressures associated with the shift in serovar prevalence.

CONCLUSIONS/SIGNIFICANCE

This work identified a shift to S. Enteritidis from the more classic S. Typhimurium, associated with iNTS in Bamako, Mali, during the period 2002-2012. This type of shift in underlying iNTS pathogens are of great importance to pediatric public health in endemic regions of sub-Saharan Africa. Additionally, this work demonstrates the utility of combining epidemiologic data, whole genome sequencing, and functional characterization in the laboratory to identify and characterize genomic changes in the isolates that may be involved with the observed shift in circulating iNTS agents.

Invasive Salmonella infections among children in Bintulu, Sarawak, Malaysian Borneo: a 6-year retrospective review

Background

Invasive Salmonella infections result in significant morbidity and mortality in developing countries. In Asia, typhoid and paratyphoid fever are reported to be the major invasive Salmonella infections, while invasive non-typhoidal Salmonella (iNTS) infections are believed to be uncommon. Data from Sarawak, in Malaysian Borneo, are limited.

Methods

A retrospective study identifying all children aged < 15 years with invasive Salmonella infections from 2011 to 2016 was conducted in Bintulu Hospital in Sarawak. Population incidences, clinical and bacterial characteristics were examined.

Results

Forty-four patients were identified during the 6-year study period: 43 had iNTS infection and 1 had typhoid fever. The average annual iNTS incidence was 32.4 per 100,000 children aged < 5 years. None of the children had malaria or HIV infection, and only 7% were severely malnourished. Salmonella Enteritidis and Salmonella Java were the commonest NTS serovars identified. Pneumonia was the most common manifestation of iNTS disease, present in 20 (47%) children. Other manifestations included gastroenteritis, fever without a source, septic arthritis and meningitis. Salmonella Enteritidis was identified in 76% of those with pneumonia, significantly more frequently than in children with other manifestations. Over 25% of children with iNTS developed severe disease and nearly 10% suffered long term morbidity or mortality. While 78% of Salmonella Java isolates were multi-drug resistant, nearly all other isolates were susceptible to most antimicrobials, including ampicillin.

Conclusions

Bintulu Division in Sarawak observed a very high incidence of childhood iNTS infections. Enteric fever was uncommon. The epidemiology of invasive Salmonella infections in Malaysian Borneo differs considerably from that of neighbouring countries in Asia.

Increasing incidence of invasive nontyphoidal Salmonella infections in Queensland, Australia, 2007-2016

Nontyphoidal Salmonella is a major contributor to the global burden of foodborne disease, with invasive infections contributing substantially to illnesses and deaths. We analyzed notifiable disease surveillance data for invasive nontyphoidal Salmonella disease (iNTS) in Queensland, Australia. We used Poisson regression to estimate incidence rate ratios by gender, age group, and geographical area over 2007–2016. There were 995 iNTS cases, with 945 (92%) confirmed by blood culture. Salmonella Virchow accounted for 254 (25%) of 1,001 unique iNTS isolates. Invasive NTS disease notification rates peaked among infants, during the summer months, and in outback Queensland where the notification rate (95% CI) was 17.3 (14.5–20.1) cases per 100,000 population. Overall, there was a 6,5% annual increase (p<0.001) in iNTS disease incidence. In conclusion, high iNTS rates among males, infants, and the elderly require investigation of household level risk factors for NTS infection. Controlling Salmonella Virchow infections is a public health priority.

We identified increasing incidence of invasive infections due to nontyphoidal Salmonella in Queensland with particularly high rates of disease among males, infants, elderly people, and cases infected with Salmonella serotype Virchow. Salmonella serotypes Choleraesuis, Dublin, and Panama had the highest proportion of invasive isolates.

Invasive Nontyphoidal Salmonella Disease in Africa

Nontyphoidal salmonellae (NTS) are a major cause of invasive (iNTS) disease in sub-Saharan Africa, manifesting as bacteremia and meningitis. Available epidemiological data indicate that iNTS disease is endemic in much of the region. Antimicrobial resistance is common and case fatality rates are high. There are well-characterized clinical associations with iNTS disease, including young age, HIV infection, malaria, malnutrition, anemia, and sickle cell disease. However, the clinical presentation of iNTS disease is often with fever alone, so clinical diagnosis is impossible without blood culture confirmation. No vaccine is currently available, making this a priority area for global health research. Over the past ten years, it has emerged that iNTS disease in Africa is caused by distinct pathovars of Salmonella Typhimurium, belonging to sequence type ST313, and Salmonella Enteritidis. These are characterized by genome degradation and appear to be adapting to an invasive lifestyle. Investigation of rare patients with primary immunodeficiencies has suggested a key role for interferon gamma-mediated immunity in host defense against NTS. This concept has been supported by recent population-based host genetic studies in African children. In contrast, immunoepidemiological studies from Africa indicate an important role for antibody for protective immunity, supporting the development of antibody-inducing vaccines against iNTS disease. With candidate O-antigen-based vaccines due to enter clinical trials in the near future, research efforts should focus on understanding the relative contributions of antibody and cell-mediated immunity to protection against iNTS disease in humans.

Extraintestinal infections caused by nontyphoidal Salmonella from a tertiary care center in India

BACKGROUND:

Infection with Salmonella has become an increasing problem worldwide. Recently, nontyphoid Salmonella (NTS) has become a global concern causing threat to the health of human. It causes gastrointestinal infection which may be self-limiting, but invasive infections may be fatal, requiring appropriate therapy. This study was done to analyze the spectrum of NTS infections causing extraintestinal infections and its susceptibility pattern from a tertiary care center in India.

MATERIALS AND METHODS:

The medical records of 27 patients whose cultures were positive for NTS between the years 2013–2016 were included in this retrospective study. The relevant demographic, clinical, and laboratory data were analyzed.

RESULTS:

Among the 27 patients, predominant patients were in the age group of 20–30 years. The male to female ratio is 1.7:1. Salmonella typhimurium was the predominant NTS isolated among 15/27 (55.5%), followed by Salmonella enteritidis 4/27 (14.8%). 18/27 (66.6%) of NTS were isolated from blood. Nalidixic acid was sensitive in 2/15 of S. typhimurium, 2/4 of S. enteritidis and 1/3 of Salmonella weltevreden, while others are nalidixic acid-resistant implying resistance to quinolones. They were sensitive to other antibiotics reported.

CONCLUSION:

This study highlights the spectrum of NTS causing extraintestinal infections which is an emerging infection occurring mostly in immunosuppressed individuals. There should be a high degree of clinical suspicion which would help in the early diagnosis and management of patients.

Epidemiology and antimicrobial resistance of invasive non-typhoidal Salmonellosis in rural Thailand from 2006-2014

INTRODUCTION

Invasive salmonellosis is a common cause of bloodstream infection in Southeast Asia. Limited epidemiologic and antimicrobial resistance data are available from the region.

METHODS

Blood cultures performed in all 20 hospitals in the northeastern province of Nakhon Phanom (NP) and eastern province of Sa Kaeo (SK), Thailand were captured in a bloodstream infection surveillance system. Cultures were performed as clinically indicated in hospitalized patients; patients with multiple positive cultures had only the first included. Bottles were incubated using the BacT/Alert system (bioMérieux, Thailand) and isolates were identified using standard microbiological techniques; all Salmonella isolates were classified to at least the serogroup level. Antimicrobial resistance was assessed using disk diffusion.

RESULTS

Salmonella was the fifth most common pathogen identified in 147,535 cultures with 525 cases (211 in Nakhon Phanom (NP) and 314 in Sa Kaeo (SK)). The overall adjusted iNTS incidence rate in NP was 4.0 cases/100,000 person-years (95% CI 3.5-4.5) and in SK 6.4 cases/100,000 person-years (95% CI 5.7-7.1; p = 0.001). The most common serogroups were C (39.4%), D (35.0%) and B (9.9%). Serogroup D predominated in NP (103/211) with 59.2% of this serogroup being Salmonella serovar Enteritidis. Serogroup C predominated in SK (166/314) with 84.3% of this serogroup being Salmonella serovar Choleraesuis. Antibiotic resistance was 68.2% (343/503) for ampicillin, 1.2% (6/482) for ciprofloxacin (or 58.1% (280/482) if both intermediate and resistant phenotypes are considered), 17.0% (87/512) for trimethoprim-sulfamethoxazole, and 12.2% (59/484) for third-generation cephalosporins (cefotaxime or ceftazidime). Multidrug resistance was seen in 99/516 isolates (19.2%).

CONCLUSIONS

The NTS isolates causing bloodstream infections in rural Thailand are commonly resistant to ampicillin, cefotaxime, and TMP-SMX. Observed differences between NP and SK indicate that serogroup distribution and antibiotic resistance may substantially differ throughout Thailand and the region.

Sexual dimorphism in bacterial infections

Background

Sex differences are important epidemiological factors that impact in the frequency and severity of infectious diseases. A clear sexual dimorphism in bacterial infections has been reported in both humans and animal models. Nevertheless, the molecular mechanisms involved in this gender bias are just starting to be elucidated. In the present article, we aim to review the available data in the literature that report bacterial infections presenting a clear sexual dimorphism, without considering behavioral and social factors.

Main body

The sexual dimorphism in bacterial infections has been mainly attributed to the differential levels of sex hormones between males and females, as well as to genetic factors. In general, males are more susceptible to gastrointestinal and respiratory bacterial diseases and sepsis, while females are more susceptible to genitourinary tract bacterial infections. However, these incidences depend on the population evaluated, animal model and the bacterial species. Female protection against bacterial infections and the associated complications is assumed to be due to the pro-inflammatory effect of estradiol, while male susceptibility to those infections is associated with the testosterone-mediated immune suppression, probably via their specific receptors. Recent studies indicate that the protective effect of estradiol depends on the estrogen receptor subtype and the specific tissue compartment involved in the bacterial insult, suggesting that tissue-specific expression of particular sex steroid receptors contributes to the susceptibility to bacterial infections. Furthermore, this gender bias also depends on the effects of sex hormones on specific bacterial species. Finally, since a large number of genes related to immune functions are located on the X chromosome, X-linked mosaicism confers a highly polymorphic gene expression program that allows women to respond with a more expanded immune repertoire as compared with men.

Conclusion

Notwithstanding there is increasing evidence that confirms the sexual dimorphism in certain bacterial infections and the molecular mechanisms associated, further studies are required to clarify conflicting data and to determine the role of specific hormone receptors involved in the gender bias of bacterial infections, as well as their potential as therapeutic targets.

Epidemiology and Genomics of Invasive Nontyphoidal Salmonella Infections in Kenya

BACKGROUND

In Kenya, invasive nontyphoidal Salmonella (iNTS) disease causes severe bacteremic illness among adults with human immunodeficiency virus (HIV) and especially among children <5 years of age coinfected with HIV or malaria, or who are compromised by sickle cell disease or severe malnutrition. The incidence of iNTS disease in children ranges from 166 to 568 cases per 100,000 persons per year.

METHODS

We review the epidemiology of iNTS disease and genomics of strains causing invasive illness in Kenya. We analyzed a total of 192 NTS isolates (114 Typhimurium, 78 Enteritidis) from blood and stools from pediatric admissions in 2005-2013. Testing for antimicrobial susceptibility to commonly used drugs and whole-genome sequencing were performed to assess prevalence and genetic relatedness of multidrug-resistant iNTS strains, respectively.

RESULTS

A majority (88/114 [77%]) of Salmonella Typhimurium and 30% (24/79) of Salmonella Enteritidis isolates tested were found to be multidrug resistant, whereas a dominant Salmonella Typhimurium pathotype, ST313, was primarily associated with invasive disease and febrile illness. Analysis of the ST313 isolates has identified genome degradation, compared with the ST19 genotype that typically causes diarrhea in humans, especially in industrialized countries, adapting a more host-restricted lifestyle typical of Salmonella Typhi infections.

CONCLUSIONS

From 2012, we have observed an emergence of ceftriaxone-resistant strains also showing reduced susceptibility to fluoroquinolones. As most cases present with nonspecific febrile illness with no laboratory-confirmed etiology, empiric treatment of iNTS disease is a major challenge in Kenya. Multidrug resistance, including to ceftriaxone, will pose further difficulty in management of iNTS disease in endemic areas.

Salmonella Infections in The Gambia, 2005-2015

BACKGROUND

There are large data gaps in the epidemiology of diseases caused by Salmonella enterica in West Africa. Regional surveillance of Salmonella infections is necessary, especially with the emergence and spread of multidrug-resistant clones.

METHODS

Data on Salmonella isolated from various clinical specimens from patients from across The Gambia were collected and analyzed retrospectively from 2005 to April 2015. Antibiotic sensitivity testing of Salmonella isolates was performed by disk diffusion method. Serotyping and serogrouping of Salmonella isolates was performed using standard microbiology techniques.

RESULTS

Two hundred three Salmonella isolates were isolated from 190 patients: 52% (106/203) from blood and 39% (79/203) from stool specimens. Salmonella was also isolated from urine, aspirates, cerebrospinal fluid, wounds, and abscesses. The prevalence of Salmonella in blood cultures was 0.8% (106/13,905). Of the serotyped salmonellae, 14% (21/152) were Salmonella enterica serovar Typhi, whereas 86% (131/152) were serovars other than Typhi (nontyphoidal Salmonella). Of the 102 typed NTS isolates, 40% (41) were Salmonella enterica serovar Typhimurium, 10% (10) were Salmonella enterica serovar Enteritidis, and 3% (3) were Salmonella enterica serovar Arizonae. Overall, 70% (142/203) of the salmonellae were pansusceptible. Multidrug resistance was found in 4% (9/203) of the isolates, 3 of which were Salmonella Enteritidis.

CONCLUSIONS

Salmonellae are associated with a wide spectrum of invasive and noninvasive infections across all ages in The Gambia. There is evidence of multidrug resistance in salmonellae that warrants vigilant monitoring and surveillance.

A Multischool Outbreak Due to Salmonella enterica serovar Napoli Associated with Elevated Rates of Hospitalizations and Bacteremia, Milan, Italy, 2014

A multischool outbreak of salmonellosis caused by Salmonella enterica serovar Napoli was investigated in the province of Milan from October to November 2014, following an increase in school absenteeism coinciding with two positive cases. Epidemiological studies detected 47 cases in four primary schools: 46 children and 1 adult woman (51.4% males and 48.6% females, median age 8.9). From these, 14 cases (29.8%) were severe and resulted in hospitalization, including 6 children (12.8%) who developed an invasive salmonellosis. The epidemic curve revealed an abnormally long incubation period, peaking 1 week after the first confirmed case. Twenty-five available isolates were typed by pulsed-field gel electrophoresis showing an identical pattern. The isolate belongs to ST474, an ST composed exclusively of Salmonella Napoli human strains isolated in France and Italy. Antibiotic resistance analysis showed resistance to aminoglycosides, correlating with the presence of the aminoglycoside resistance gene aadA25 in its genome. Trace-back investigations strongly suggested contaminated ham as the most likely food vehicle, which was delivered by a common food center on 21 October. Nevertheless, this ingredient could not be retrospectively investigated since it was no longer available at the repository. This represents the largest Salmonella Napoli outbreak ever reported in Italy and provides a unique scenario for studying the outcome of salmonellosis caused by this emerging and potentially invasive nontyphoidal serotype.

Global burden of invasive nontyphoidal Salmonella disease, 2010(1)

Nontyphoidal Salmonella is a major cause of bloodstream infections worldwide, and HIV-infected persons and malaria-infected children are at increased risk for the disease. We conducted a systematic literature review to obtain age group-specific, population-based invasive nontyphoidal Salmonella (iNTS) incidence data. Data were categorized by HIV and malaria prevalence and then extrapolated by using 2010 population data. The case-fatality ratio (CFR) was determined by expert opinion consensus. We estimated that 3.4 (range 2.1-6.5) million cases of iNTS disease occur annually (overall incidence 49 cases [range 30-94] per 100,000 population). Africa, where infants, young children, and young adults are most affected, has the highest incidence (227 cases [range 152-341] per 100,000 population) and number of cases (1.9 [range 1.3-2.9] million cases). An iNTS CFR of 20% yielded 681,316 (range 415,164-1,301,520) deaths annually. iNTS disease is a major cause of illness and death globally, particularly in Africa. Improved understanding of the epidemiology of iNTS is needed.

Clinical features and outcome of typhoid fever and invasive non-typhoidal salmonellosis in a tertiary hospital in Belgium: analysis and review of the literature

OBJECTIVES

Typhoid fever (TF) occurs rarely in industrialized countries because of advances in health care and improvement of drinking water. Conversely, non-typhoid salmonellosis (NTS) remains widespread, because of food contamination or asymptomatic carriage. Non-typhoid salmonellosis can be severe when becoming invasive non-typhoid salmonellosis (iNTS). Although established prognostic indicators of the two pathologies are different, direct comparisons between iNTS and TF in the literature remain scarce. The purpose of this study was to analyse and compare demographic, clinical features and outcome of hospitalized patients with TF and iNTS.

METHODS

Demographic, clinical features and outcome were retrospectively analysed in a series of patients hospitalized between 2007 and 2012.

RESULTS

A total of 33 patients were enrolled, including 13 with established TF and 20 with iNTS. No differences between TF and iNTS patients were observed in incidence of fever, abdominal cramps, diarrhoea, headache, nausea and vomiting and duration of antibiotic therapy (≤ 7 days in both groups). Although the clinical outcome of TF patients was identical to that of iNTS patients, including incidence of complications, length of hospitalization and mortality (1/13 (7.7%) vs 2/20 (10%), P = 0.43), comorbidities were less frequent in the TF group than in the iNTS group (2/13 vs 15/20, P = 0.003).

CONCLUSION

The clinical profile and outcome of TF patients are similar to those with iNTS. Although comorbidities are more often associated with iNTS, the results of our study suggest that clinical management of these two diseases should remain similar.

Population-based epidemiology and microbiology of community-onset bloodstream infections

Bloodstream infection (BSI) is a major cause of infectious disease morbidity and mortality worldwide. While a positive blood culture is mandatory for establishment of the presence of a BSI, there are a number of determinants that must be considered for establishment of this entity. Community-onset BSIs are those that occur in outpatients or are first identified <48 h after admission to hospital, and they may be subclassified further as health care associated, when they occur in patients with significant prior health care exposure, or community associated, in other cases. The most common causes of community-onset BSI include Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. Antimicrobial-resistant organisms, including methicillin-resistant Staphylococcus aureus and extended-spectrum β-lactamase/metallo-β-lactamase/carbapenemase-producing Enterobacteriaceae, have emerged as important etiologies of community-onset BSI.

Osteomyelitis, discitis, epidural and psoas abscess secondary to Salmonella enterica in a man with diabetes mellitus and newly diagnosed α-thalassaemia trait

We report the case of a 65-year-old man with type 2 diabetes mellitus and α-thalassaemia trait. Investigations for relapsing and remitting fever found vertebral osteomyelitis, discitis and epidural and psoas abscess secondary to Salmonella enterica.

Antimicrobial use in critically ill horses

OBJECTIVE

To discuss controversies surrounding antimicrobial use in critically ill horses.

DATA SOURCES

PubMed searches from 1970-present for terms including, but not limited to: "horse," "foal," "antimicrobial," "prophylaxis," "infection," "surgery," "sepsis," and "antimicrobial resistance."

HUMAN DATA SYNTHESIS

Increasing bacterial antimicrobial resistance has changed first-line antimicrobial choices and prompted shortening of the duration of prophylactic and therapeutic treatment. The need to decrease bacterial resistance development to critically important antimicrobials has been highlighted.

VETERINARY DATA SYNTHESIS

Veterinary medicine has followed a similar trend but often without a high-level evidence. Common dilemmas include diseases in which the theoretically most effective drug is a reserved antimicrobial, the inability to differentiate infectious from noninfectious disease, the duration and necessity of prophylactic antimicrobials and use of antimicrobials in primary gastrointestinal disease. These problems are illustrated using examples of purulent infections, neonatal sepsis, colic surgery, and treatment of colitis. Although enrofloxacin, cephalosporins, and doxycycline, in contrast to gentamicin, reach therapeutic concentrations within the lungs of healthy horses, the first two should not be used as first line treatment due to their reserved status. Due to the high risk of bacterial sepsis, antimicrobial treatment remains indispensable in compromised neonatal foals but shortening the length of antimicrobial treatment might be prudent. One prospective randomized study demonstrated no difference between 3 and 5 days of perioperative antimicrobial treatment in colic surgery but shorter durations were not evaluated. High-level evidence to recommend antimicrobial treatment of adult horses with undifferentiated diarrhea does not exist.

CONCLUSIONS

Few evidence-based recommendations can be made. Commonly used antimicrobial combinations remain the mainstay for treating purulent infections. Antimicrobial treatment for compromised foals should not extend beyond recovery. Continuation of prophylactic antimicrobials >3 days is likely unnecessary after colic surgery; shorter durations might be equally effective. Antimicrobial prophylaxis in adult horses with diarrhea is unlikely to be beneficial.

Epidemiological investigation of an outbreak of salmonellosis in Gyeongju, Korea

Objectives

A salmonellosis outbreak occurred within a community of Gyeongju residents who ingested catered food from a wedding in June 2009. We aimed to epidemiologically investigate the probable vehicle of the infection.

Methods

We conducted a retrospective cohort study on 34 local residents who ingested the wedding food.

Results

Among the 34 residents, 31 (91.2%) reported symptoms of infection after eating the food. Among all of the wedding foods, pan-fried foods were highly associated with the diarrheal attack rate. On bacteriological examination, Salmonella species were detected in the pan-fried foods among the leftover foods and in 17 of the 31 stool specimens from the cases. There were five different types of pan-fried foods, but the onset of symptoms was independent of the ingredients used. We found that the pan-fried food was prepared at a food store in Seoul and that eggs were a common ingredient.

Conclusions

The major cause of the salmonellosis in this population was presumed to be the pan-fried food prepared with contaminated eggs. These food items might have been partially undercooked because of their irregular shape, which allowed the Salmonella species to survive and multiply before ingestion.

Increasing rates of Salmonella Paratyphi A and the current status of its vaccine development

Enteric fever caused by Salmonella enterica serovar Typhi and Salmonella enterica serovar Paratyphi is still a major disease burden mainly in developing countries. Previously, S. Typhi was believed to be the major cause of enteric fever. The real situation is now becoming clear with reports emerging from many Asian countries of S. Paratyphi, mostly S. Paratyphi A, causing a substantial number of cases of enteric fever. Although there have been advances in the use of the currently available typhoid vaccines and in the development of newer typhoid vaccines, paratyphoid vaccine development is lagging behind. Since the disease caused by S. Typhi and S. Paratyphi are clinically indistinguishable and are commonly termed 'enteric' fever, it will be necessary to have a vaccine available against both S. Typhi and S. Paratyphi A as a bivalent 'enteric fever vaccine'.

The role of the st313-td gene in virulence of Salmonella Typhimurium ST313

Multidrug-resistant Salmonella enterica serovar Typhimurium ST313 has emerged in sub-Saharan Africa causing severe infections in humans. Therefore, it has been speculated that this specific sequence type, ST313, carries factors associated with increased pathogenicity. We assessed the role in virulence of a gene with a yet unknown function, st313-td, detected in ST313 through comparative genomics. Additionally, the structure of the genomic island ST313-GI, harbouring the gene was determined. The gene st313-td was cloned into wild type S. Typhimurium 4/74 (4/74-C) as well as knocked out in S. Typhimurium ST313 02–03/002 (Δst313-td) followed by complementation (02-03/002-C). Δst313-td was less virulent in mice following i.p. challenge than the wild type and this phenotype could be partly complemented in trans, indicating that st313-td plays a role during systemic infection. The gene st313-td was shown not to affect invasion of cultured epithelial cells, while the absence of the gene significantly affects uptake and intracellular survival within macrophages. The gene st313-td was proven to be strongly associated to invasiveness, harboured by 92.5% of S. Typhimurium blood isolates (n = 82) and 100% of S. Dublin strains (n = 50) analysed. On the contrary, S. Typhimurium isolates of animal and food origin (n = 82) did not carry st313-td. Six human, non-blood isolates of S. Typhimurium from Belarus, China and Nepal harboured the gene and belonged to sequence types ST398 and ST19. Our data showed a global presence of the st313-td gene and in other sequence types than ST313. The gene st313-td was shown to be expressed during logarithmic phase of growth in 14 selected Salmonella strains carrying the gene. This study reveals that st313-td plays a role in S. Typhimurium ST313 pathogenesis and adds another chapter to understanding of the virulence of S. Typhimurium and in particular of the emerging sequence type ST313.

Cross-reactive immune response elicited by parenteral Vi polysaccharide typhoid vaccine against non-typhoid Salmonellae

BACKGROUND

Despite 155000 deaths and over 90 million cases - and the current emergence of antimicrobial resistance - no vaccines are available against non-typhoid Salmonellae (NTS). We recently presented immunological arguments for using the oral Salmonella Typhi Ty21a as surrogate vaccine against NTS strains: Ty21a elicits intestinal antibodies against typhoidal O-9,12 antigen, and numerous NTS strains share one or both of these structures with S. Typhi. The Vi polysaccharide vaccine can, presumably because of contaminating typhoidal lipopolysaccharide, also elicit a humoral response to O-9,12, although a lower one in magnitude than the Ty21a. In this study, the Vi vaccine was explored for cross-reactive immune response to various NTS strains, and compared to that elicited by the Ty21a vaccine.

MATERIALS AND METHODS

Volunteers immunized with the Vi polysaccharide (Typherix(®); n=25) were investigated for circulating plasmablasts secreting antibodies reactive with six NTS serotypes. The results were compared to those for 25 age- and gender-matched volunteers vaccinated with Ty21a (Vivotif(®)), as partly presented in our previous study. The cross-reactive plasmablasts elicited by the Vi vaccine were also analyzed for homing receptor expressions.

RESULTS

49 out of 50 vaccinees showed a cross-reactive plasmablast response against S. Enteritidis sharing both O-9 and O-12 antigens with S. Typhi (mean: 95%CI 37: 19-55 and 363: 234-493 plasmablasts/10(6) PBMC in the Vi and the Ty21a group, respectively). The response against strains only sharing O-12 was weaker (22: 8-38 and 222: 105-338 against S. Typhimurium). Strains without typhoidal O-antigens generated no significant reactivity. The cross-reactive plasmablasts elicited by the Vi vaccine had systemic homing properties.

CONCLUSIONS

The Vi vaccine elicited an immune response cross-reactive with several NTS strains. This response was lower than that in Ty21a-vaccinated volunteers. The clinical significance of these responses deserves further research with respect to both gastrointestinal and invasive NTS (iNTS) disease.

Genomic characterisation of invasive non-typhoidal Salmonella enterica Subspecies enterica Serovar Bovismorbificans isolates from Malawi

Background

Invasive Non-typhoidal Salmonella (iNTS) are an important cause of bacteraemia in children and HIV-infected adults in sub-Saharan Africa. Previous research has shown that iNTS strains exhibit a pattern of gene loss that resembles that of host adapted serovars such as Salmonella Typhi and Paratyphi A. Salmonella enterica serovar Bovismorbificans was a common serovar in Malawi between 1997 and 2004.

Methodology

We sequenced the genomes of 14 Malawian bacteraemia and four veterinary isolates from the UK, to identify genomic variations and signs of host adaptation in the Malawian strains.

Principal Findings

Whole genome phylogeny of invasive and veterinary S. Bovismorbificans isolates showed that the isolates are highly related, belonging to the most common international S. Bovismorbificans Sequence Type, ST142, in contrast to the findings for S. Typhimurium, where a distinct Sequence Type, ST313, is associated with invasive disease in sub-Saharan Africa. Although genome degradation through pseudogene formation was observed in ST142 isolates, there were no clear overlaps with the patterns of gene loss seen in iNTS ST313 isolates previously described from Malawi, and no clear distinction between S. Bovismorbificans isolates from Malawi and the UK.

The only defining differences between S. Bovismorbificans bacteraemia and veterinary isolates were prophage-related regions and the carriage of a S. Bovismorbificans virulence plasmid (pVIRBov).

Conclusions

iNTS S. Bovismorbificans isolates, unlike iNTS S. Typhiumrium isolates, are only distinguished from those circulating elsewhere by differences in the mobile genome. It is likely that these strains have entered a susceptible population and are able to take advantage of this niche. There are tentative signs of convergent evolution to a more human adapted iNTS variant. Considering its importance in causing disease in this region, S. Bovismorbificans may be at the beginning of this process, providing a reference against which to compare changes that may become fixed in future lineages in sub-Saharan Africa.

Bacteraemia and meningitis caused by non-typhoidal Salmonella (including serovars Typhimurium, Enteritidis and Bovismorbificans) are a serious health issue in sub-Saharan Africa, particularly in young children and HIV-infected adults. Previous work has indicated that a distinct S. Typhimurium sequence type, ST313, has evolved and spread in these countries, and may be more human-adapted than isolates found in the developed world. We therefore investigated the genomes of Salmonella enterica serovar Bovismorbificans bacteraemia isolates from Malawi and compared them to genomes of veterinary S. Bovismorbificans isolates from the UK using Next Generation Sequencing Technology and subsequent genomic comparisons to establish if there is a genetic basis for this increase in invasive disease observed among African NTS. Contrary to the previous findings for S. Typhimurium, where a distinct ST is found only in sub-Saharan Africa, we discovered that the S. Bovismorbificans isolates from Malawi belong to the most common ST of the serovar and the genome is highly conserved across all sequenced isolates. The major differences between UK veterinary and African human isolates were due to prophage regions inserted into the genomes of African isolates, coupled with a higher prevalence of a virulence plasmid compared to the UK isolates.

A retrospective study of secondary bacteraemia in hospitalised adults with community acquired non-typhoidal Salmonella gastroenteritis

Background

The clinical significance of bacteraemia secondary to non-typhoidal Salmonella (NTS) gastroenteritis in hospitalised adults is uncertain.

Methods

Adults admitted to a hospital in Liverpool, UK, with NTS gastroenteritis were identified using hospital discharge data and laboratory records. Patients with known HIV infection were excluded. Risk factors for a complicated or fatal course were determined.

Results

Between 1982 and 2006 inclusive, 633 adults were identified. Serovars causing infection included Enteritidis (46.6%), Typhimurium (27.6%) and Virchow (4.9%). A blood culture was taken in 364 (57.5%) patients who were generally sicker than those who were not cultured. Bacteraemia was detected in 63 (17.3%) patients who had blood cultures taken (63/633 (10.0%) of all patients). Bacteraemia was more common in those aged ≥ 65 years (p < 0.001) and in those aged < 65 years who had an underlying chronic disease. A complicated course occurred in 91 (25.0%) patients who had had a blood culture taken (148/633 (23.4%) of all patients). Independent factors associated with a complicated or fatal course among the patients investigated with a blood culture were bacteraemia (Adjusted Odds Ratio 5.34, 95% CI 2.86–9.95); new onset confusion or coma (AOR 4.80, 95% CI 1.91–12.07); prolonged symptoms prior to admission (AOR 2.48, 95% CI 1.44–4.27); dehydration (AOR1.90, 95% CI 1.07–3.38); and absence of fever (AOR 0.56, 95% CI 0.32–0.95). The 30 day attributable case fatality for all patients was 1.5%.

Conclusions

In this study secondary bacteraemia, as well as other clinical factors, was independently associated with a complicated or fatal course in non-HIV infected adults admitted to hospital with NTS gastroenteritis.

Invasive non-typhoidal salmonella infection with multifocal seeding in an immunocompetent host: an emerging disease in the developed world

We report an immunocompetent 24-year-old man who presented with a severe, invasive non-typhoidal salmonella (iNTS) infection. He presented with lumbar back pain associated with fever and rigours, which had been preceded by diarrhoea. Blood cultures grew Salmonella enteritidis. An MRI scan of his pelvis and spine showed that he had a small gluteal abscess and sacroiliitis. His condition subsequently deteriorated due to the development of a secondary pneumonia and respiratory failure. He was managed conservatively with 2 weeks of intravenous ceftriaxone, followed by 6 weeks of oral ciprofloxacin. Detailed investigations did not reveal any predisposing factors or evidence of an underlying immunodeficiency. Follow-up showed complete resolution of symptoms with no long-term sequelae.

Live oral typhoid vaccine Salmonella Typhi Ty21a - a surrogate vaccine against non-typhoid salmonella?

BACKGROUND

Non-typhoid Salmonella (NTS) is a leading cause of food-borne illness with more than 90 million annual cases and an emerging antimicrobial resistance among the strains worldwide. Paradoxically, no vaccines are available against these pathogens. Numerous NTS strains share surface O-antigens with Salmonella enterica serotype Typhi. As intestinal antibodies against O-antigens have proven protective against NTS in animal experiments, it appears conceivable that the oral whole-cell typhoid vaccine, Salmonella Typhi Ty21a (Vivotif(®)), which effectively elicits intestinal antibodies against O-antigens, could exhibit cross-protective efficacy against NTS. We sought immunological evidence in support of cross-protective efficacy of Ty21a against NTS.

MATERIALS AND METHODS

35 volunteers receiving Ty21a vaccine and five patients with enteric fever were investigated with ELISPOT for circulating plasmablasts secreting antibodies reactive with Salmonella Typhi and six different NTS serotypes. These plasmablasts were also analysed for homing receptor expressions.

RESULTS

In all vaccinees and patients, a strong gut-directed cross-reactive plasmablast response was found against serotypes sharing the two O-antigens with Salmonella Typhi (O-9,12) (in vaccinees, mean: 95%CI 268: 228-508 and 363: 234-493 plasmablasts/10(6)PBMC against Salmonella Typhi and Enteritidis). Responses against strains sharing one O-antigen (O-12) were weaker (222: 105-338 against Salmonella Typhimurium), while no significant reactivity was detected against strains without typhoidal O-antigens.

CONCLUSIONS

Intestinal antibodies against O-antigens protect against NTS in animal experiments. Ty21a was found to elicit intestinal immune responses cross-reactive with NTS strains sharing O-antigens with Ty21a. These include the most common NTS, Salmonella Enteritidis and Typhimurium. The data suggest that Ty21a may have cross-protective efficacy against numerous NTS strains.

Invasive non-typhoidal salmonella disease: an emerging and neglected tropical disease in Africa

Invasive strains of non-typhoidal salmonellae have emerged as a prominent cause of bloodstream infection in African adults and children, with an associated case fatality of 20-25%. The clinical presentation of invasive non-typhoidal salmonella disease in Africa is diverse: fever, hepatosplenomegaly, and respiratory symptoms are common, and features of enterocolitis are often absent. The most important risk factors are HIV infection in adults, and malaria, HIV, and malnutrition in children. A distinct genotype of Salmonella enterica var Typhimurium, ST313, has emerged as a new pathogenic clade in sub-Saharan Africa, and might have adapted to cause invasive disease in human beings. Multidrug-resistant ST313 has caused epidemics in several African countries, and has driven the use of expensive antimicrobial drugs in the poorest health services in the world. Studies of systemic cellular and humoral immune responses in adults infected with HIV have revealed key host immune defects contributing to invasive non-typhoidal salmonella disease. This emerging pathogen might therefore have adapted to occupy an ecological and immunological niche provided by HIV, malaria, and malnutrition in Africa. A good understanding of the epidemiology of this neglected disease will open new avenues for development and implementation of vaccine and public health strategies to prevent infections and interrupt transmission.

Seasonality in human zoonotic enteric diseases: a systematic review

Background

Although seasonality is a defining characteristic of many infectious diseases, few studies have described and compared seasonal patterns across diseases globally, impeding our understanding of putative mechanisms. Here, we review seasonal patterns across five enteric zoonotic diseases: campylobacteriosis, salmonellosis, vero-cytotoxigenic Escherichia coli (VTEC), cryptosporidiosis and giardiasis in the context of two primary drivers of seasonality: (i) environmental effects on pathogen occurrence and pathogen-host associations and (ii) population characteristics/behaviour.

Methodology/Principal Findings

We systematically reviewed published literature from 1960–2010, resulting in the review of 86 studies across the five diseases. The Gini coefficient compared temporal variations in incidence across diseases and the monthly seasonality index characterised timing of seasonal peaks. Consistent seasonal patterns across transnational boundaries, albeit with regional variations was observed. The bacterial diseases all had a distinct summer peak, with identical Gini values for campylobacteriosis and salmonellosis (0.22) and a higher index for VTEC (Gini = 0.36). Cryptosporidiosis displayed a bi-modal peak with spring and summer highs and the most marked temporal variation (Gini = 0.39). Giardiasis showed a relatively small summer increase and was the least variable (Gini = 0.18).

Conclusions/Significance

Seasonal variation in enteric zoonotic diseases is ubiquitous, with regional variations highlighting complex environment-pathogen-host interactions. Results suggest that proximal environmental influences and host population dynamics, together with distal, longer-term climatic variability could have important direct and indirect consequences for future enteric disease risk. Additional understanding of the concerted influence of these factors on disease patterns may improve assessment and prediction of enteric disease burden in temperate, developed countries.

Epidemiology, disease spectrum and economic burden of non-typhoidal Salmonella infections in Taiwan, 2006-2008

The purpose of this study was to understand the seasonal, geographical and clinical characteristics of Taiwanese patients hospitalized for non-typhoidal Salmonella (NTS) infections and their economic burden. Hospital data obtained from the Taiwan National Health Insurance (NHI) database between 2006 and 2008 were analysed. Infants had the highest annual incidence of 525 cases/100 000 person-years. Elderly patients aged >70 years had the highest in-hospital mortality rate (2·6%). Most (82·6%) gastroenteritis occurred in children aged <10 years. Septicaemia, pneumonia, arthritis and osteomyelitis occurred mainly in patients aged >50 years. A median medical cost for NTS-associated hospitalizations was higher for patients with septicaemia than for those with gastroenteritis. Seasonal variation of NTS-associated hospitalizations was correlated with temperature in different areas of Taiwan. In summary, infants had a high incidence of NTS-associated hospitalizations. However, the elderly had a higher in-hospital mortality rate and more invasive NTS infections than children.

Salmonella infections: an update on epidemiology, management, and prevention

Salmonella species are a group of Gram-negative enterobacteria and known human pathogens in developing as well as industrialized countries. Despite significant advances in sanitation, provision of potable water, and highly controlled food chain surveillance, transmission of Salmonella spp. continues to affect communities, preferentially children, worldwide. This review summarizes updated concepts on typhoidal and non-typhoidal Salmonella infections, starting with a historical perspective that implicates typhoid Salmonella as a significant human pathogen since ancient times. We describe the epidemiology of this pathogen with emphasis on the most recent non-typhoidal Salmonella outbreaks in industrialized countries and continued outbreaks of typhoid Salmonella in underserved countries. An overview of clinical aspects of typhoid and non-typhoid infections in developing and industrialized countries, respectively, is provided, followed by a description on current treatment concepts and challenges treating multidrug-resistant Salmonella infections. We conclude with prevention recommendations, and recent research studies on vaccine prevention.

Invasive nontyphoidal Salmonella disease: epidemiology, pathogenesis and diagnosis

PURPOSE OF REVIEW

This review highlights and discusses important publications over the past 12 months providing new insights on invasive nontyphoidal Salmonella (iNTS) disease.

RECENT FINDINGS

There have been informative new estimates of the burden of iNTS in Asia and in high-resource, low-incidence settings. Important information has emerged in the last year about the relationships between HIV, malaria, iNTS and typhoid fever in adults and children in Africa. HIV causes susceptibility to iNTS disease, but has been shown to be protective against typhoid fever. Clinical guidelines for presumptive diagnosis frequently fail to identify iNTS disease in Africa, and there remains a need for improved diagnostic tools. Experimental studies in humans have helped us to understand the intracellular pathogenesis of iNTS and to direct the search for appropriate protein vaccine targets.

SUMMARY

The most important remaining gap in our knowledge is probably an understanding of how NTS is transmitted, and the nature of the relationship between diarrhoeal disease, carriage and invasive disease in Africa, so that diagnostic and prevention tools can be appropriately directed.

Molecular characterization of a functional type VI secretion system in Salmonella enterica serovar Typhi

The type VI secretion system (T6SS) of Salmonella enterica serovar Typhi (S. typhi) is associated with Salmonella pathogenicity island 6 (SPI-6). Though the T6SS gene cluster is intact in S. typhi, the protein complex is believed to be non-functional due to the presence of a pseudogene form of SciI (VipB homolog), a key component. We detected the SciK-his6 in the supernatant of the wild type strain of S. typhi containing the plasmid over-expressing SciK (hcp homolog) with a his6 epitope at the C-terminus, which suggested that the T6SS in S. typhi is functional. We also identified four genes that were essential to T6SS function: sciC (vasA homolog), sciS (vasK homolog), sciG (clpV homolog), and vrgS (vgrG homolog). Further analysis revealed that S. typhi T6SS is cytotoxic to human epithelial cells, but does not influence bacterial growth and mobility. RcsB, PmrA, and Hfq were identified as regulators of S. typhi T6SS gene expression; however, PhoP appears to not be involved. Taken together, the data demonstrate the functionality of S. typhi T6SS and confirm the important role of T6SS for S. typhi's ability to invade and infect epithelial cells.