Salmonella subtypes with increased MICs for azithromycin in travelers returned to The Netherlands

Enteric Fever: Diagnostic Challenges and the Importance of Early Intervention

Enteric fever is a systemic infection caused by highly virulent Salmonella enterica serovars: Typhi and Paratyphi. Diagnosis of enteric fever is challenging due to a wide variety of clinical features which overlap with other febrile illnesses. The current diagnostic methods are limited because of the suboptimal sensitivity of conventional tests like blood culture in detecting organisms and the invasive nature of bone marrow culture. It emphasizes the need to develop improved and more reliable diagnostic modalities. The rising rates of multidrug-resistant Salmonella strains call for an accurate understanding of the current management of the disease. Proper public health measures and large-scale immunization programs will help reduce the burden of the disease. A comprehensive surveillance system can help detect the chronic carrier state and is crucial in understanding antibiotic susceptibility patterns. We conducted an all-language literature search on Medline, Cochrane, Embase, and Google Scholar till May 2022. The following search words and medical subject headings (MeSH) were used: "enteric fever," "Salmonella Typhi," "multidrug-resistant Salmonella," chronic carrier state," "Salmonella detection, "and "typhoid vaccine." We reviewed the literature on clinical features, pathophysiology, new diagnostic tests, and interventions to prevent the disease. This article explores enteric fever and its various clinical features and addresses the emerging threat of multidrug resistance. It focuses on novel methods for diagnosis and prevention strategies, including vaccines and the use of surveillance systems employed across different parts of the world.

A Systematic Review of the Diagnosis and Treatment of Non-Typhoid Salmonella Spondylodiscitis in Immunocompetent Children

The aim of this systematic review is to distinguish the clinical features of immunocompetent children with non-typhoid Salmonella spondylodiscitis and summarize the diagnosis, diagnostic tools, and treatment methods to guide clinicians. The review was conducted according to the preferred PRISMA guidelines. We conducted a literature search in the PubMed, Embase, and Cochrane Library databases. Article screening, data extraction, and study evaluation were performed by two independent reviewers. A total of 20 articles, published between 1977 and 2020, were selected, which included 21 patients with average age of 12.76 years (range, 2-18) without comorbidities; in total, 19% of the patients had positive blood cultures for non-typhoid Salmonella, and 80.9% underwent either CT-guided or open biopsy, which were positive for NTS. All infections were monomicrobial, and 11 different serotypes of non-typhoid Salmonella were identified. Analyzing the reviewed cases, 52.4% of the patients presented with fever, 90.5% had localized pain, and only 19% had gastroenteritis. The most common level of discitis was the lumbar region, especially the L4/L5 level. Primarily, third-generation cephalosporin was administered, and antibiotic treatment was given for an average of 9.6 weeks. Non-typhoid Salmonella spondylodiscitis is a rare clinical entity in healthy and immunocompetent children. The identification of the responsible organism is essential to guide antibiotic therapy and define the treatment duration. A significant limiting factor in this systematic review was the lack of published research articles and case series due to the rarity of the disease.

Discovery and characterization of a new genotype of Salmonella enterica serovar Bareilly isolated from diarrhea patients of food-borne outbreaks

Since the first food-borne outbreak of Salmonella enterica serovar Bareilly in the UK (2010), it has been recognized as a new type of food-borne pathogen in S. enterica. To detect and characterize this new serovar pathogen in South Korea, a total of 175 Salmonella strains was isolated and 31 isolates were identified as S. Bareilly from various food-borne outbreaks between 2014 and 2018. While pulsed-field gel electrophoresis (PFGE) analysis using XbaI revealed two major groups (A and B) each with two subgroups (A1, A2/B1, B2), average nucleotide identity (ANI), single nucleotide polymorphism (SNP), and in silico multilocus sequence typing (MLST) analyses confirmed only two major groups. Interestingly, extended SNP analysis with 67 S. Bareilly strains from outbreaks in other countries revealed that A group strains between 2014 and 2016 shared a close evolutionary relationship with the strains from outside of South Korea; however, the B group strains in 2018 were located in a separate SNP tree branch. These findings suggest that the A group may share common ancestor with the strains of previous outbreaks in the UK or other countries, while the B group is a new genotype. Comparative virulence factor (VF) analysis between the A and B group strains showed that S. Bareilly in the B group has more various than that of the A group. A comparative biofilm formation assay supports for this, which B group strain GG-21 has higher biofilm formation activity than A group strain GG-07. Antibiotic susceptibility test of 31 S. Bareilly strains revealed high susceptibility to 17 tested antibiotics, suggesting that S. Bareilly can be easily treated by antibiotics.

Disc Diffusion Testing of Azithromycin Against Clinical Isolates of Typhoidal Salmonellae: A Diagnostic Conundrum

Introduction: Typhoid remains a major healthcare problem in low and middle-income countries. The emergence of extremely drug-resistant (XDR) typhoid strains from the Indian subcontinent has led to very limited therapeutic options. Azithromycin being the only oral option for XDR typhoid faces a threat of rapid resistance due to its overuse after the COVID-19 pandemic.

Objective: To evaluate the reliability of azithromycin disc diffusion testing against clinical isolates of typhoidal salmonellae in comparison with E-test minimum inhibitory concentrations (MICs).

Study design: This is a cross-sectional validation study.

Place and duration of the study: The Department of Microbiology, Pakistan Navy Ship Shifa hospital, Karachi from June 1 to December 31, 2020.

Methodology: Antimicrobial susceptibility was performed by Kirby Bauer disc diffusion method for 60 isolates including Salmonella enterica ser. Typhi and Paratyphi A using Clinical Laboratory Standard Institute (CLSI) guidelines. MICs by the E-test method were determined for Azithromycin only.

Results: A significant proportion of the isolates (55%) had high azithromycin MIC in the wild-type distribution range (8-16 µg/ml). Ten (16.6%) isolates showed false resistance, i.e., zone diameter <13 mm by disc diffusion method when compared to E-test MIC results. Isolates with MICs close to breakpoint, i.e., 16 µg/ml were more likely to show discordant results. The sensitivity, specificity, negative predictive value, positive predictive value, and diagnostic accuracy of the disc diffusion method versus E-test were 100%, 83%, 100%, 9%, and 83%, respectively.

Conclusions: Disc diffusion method as recommended by CLSI is not reliable for azithromycin susceptibility testing particularly for isolates with high MICs in the susceptible range. The E-test method may be a better alternative to disc diffusion provided appropriate training is done prior to its application.

Antibiotic resistome of Salmonella typhi: molecular determinants for the emergence of drug resistance

Resistome is a cluster of microbial genes encoding proteins with necessary functions to resist the action of antibiotics. Resistome governs essential and separate biological functions to develop resistance against antibiotics. The widespread clinical and nonclinical uses of antibiotics over the years have combined to select antibiotic-resistant determinants and develop resistome in bacteria. At present, the emergence of drug resistance because of resistome is a significant problem faced by clinicians for the treatment of Salmonella infection. Antibiotic resistome is a dynamic and ever-expanding component in Salmonella. The foundation of resistome in Salmonella is laid long before; therefore, the antibiotic resistome of Salmonella is reviewed, discussed, and summarized. We have searched the literature using PubMed, MEDLINE, and Google Scholar with related key terms (resistome, Salmonella, antibiotics, drug resistance) and prepared this review. In this review, we summarize the status of resistance against antibiotics in S. typhi, highlight the seminal work in the resistome of S. typhi and the genes involved in the antibiotic resistance, and discuss the various methods to identify S. typhi resistome for the proactive identification of this infection and quick diagnosis of the disease.

Salmonella Osteomyelitis in Adults: A Systematic Review

The aim of this systematic review was to characterize the clinical features of adults with Salmonella osteomyelitis and summarize diagnosis and treatment methods to provide guidance for clinicians. This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines. We conducted a literature search in the PubMed, EMBASE, and Cochrane Library databases. Article screening and data extraction were performed by two reviewers individually. All the included studies were independently evaluated by two reviewers using the Methodological Index for Non‐Randomized Studies (MINORS) criteria. A total of 67 articles published between 1970 and 2019 were selected, which include 69 patients with an average age of 47.5 years (range, 18–79).The majority of cases (47.76%) occurred in immunocompetent adults without common risk factors. Aspiration and biopsy cultures were all positive in Salmonella osteomyelitis patients who underwent aspiration or biopsy. All infections were monomicrobial, and a total of 12 different serotypes were identified. The three most commonly reported Salmonella serotypes were Salmonella typhi (19 cases), Salmonella typhimurium (12 cases), and Salmonella enteritidis (11 cases). Only 12 of the 67 cases in our data (17.91%) had diarrhea symptoms, and 44 of the 67 cases (65.67%) had fever symptoms. Fifty‐nine of the 67 cases (88.06%) had local inflammatory manifestations, such as erythema, swelling, and tenderness in the affected area. The commonly reported involved sites were the vertebrae, femur, and tibia. Antibiotic therapy alone was utilized in 30 cases, and 24 patients (80.00%) were eventually cured. In total, 75.68% of patients achieved satisfactory results after treatment with surgery and antibiotics. Third‐generation cephalosporins were most commonly utilized, and antibiotic treatment was administered for an average of 11.3 weeks (95% CI, 8.31–14.37 weeks). Salmonella osteomyelitis should be considered in patients without any common risk factors. Aspiration or biopsy can facilitate the identification of pathogens to guide antibiotic choice. Empirical therapy with a third‐generation cephalosporin is recommended until the susceptibility of the strain is determined.

Travel-Related Antimicrobial Resistance: A Systematic Review

There is increasing evidence that human movement facilitates the global spread of resistant bacteria and antimicrobial resistance (AMR) genes. We systematically reviewed the literature on the impact of travel on the dissemination of AMR. We searched the databases Medline, EMBASE and SCOPUS from database inception until the end of June 2019. Of the 3052 titles identified, 2253 articles passed the initial screening, of which 238 met the inclusion criteria. The studies covered 30,060 drug-resistant isolates from 26 identified bacterial species. Most were enteric, accounting for 65% of the identified species and 92% of all documented isolates. High-income countries were more likely to be recipient nations for AMR originating from middle- and low-income countries. The most common origin of travellers with resistant bacteria was Asia, covering 36% of the total isolates. Beta-lactams and quinolones were the most documented drug-resistant organisms, accounting for 35% and 31% of the overall drug resistance, respectively. Medical tourism was twice as likely to be associated with multidrug-resistant organisms than general travel. International travel is a vehicle for the transmission of antimicrobial resistance globally. Health systems should identify recent travellers to ensure that adequate precautions are taken.

Epidemiological and Clinical Characteristics of International Travelers with Enteric Fever and Antibiotic Resistance Profiles of Their Isolates: a GeoSentinel Analysis

Enteric fever, caused by Salmonella enterica serovar Typhi (S Typhi) and S. enterica serovar Paratyphi (S Paratyphi), is a common travel-related illness. Limited data are available on the antimicrobial resistance (AMR) patterns of these serovars among travelers. Records of travelers with a culture-confirmed diagnosis seen during or after travel from January 2007 to December 2018 were obtained from GeoSentinel. Traveler demographics and antimicrobial susceptibility data were analyzed. Isolates were classified as nonsusceptible if intermediate or resistant or as susceptible in accordance with the participating site's national guidelines. A total of 889 travelers (S Typhi infections, n = 474; S Paratyphi infections, n = 414; coinfection, n = 1) were included; 114 (13%) were children of <18 years old. Most individuals (41%) traveled to visit friends and relatives (VFRs) and acquired the infection in South Asia (71%). Child travelers with S Typhi infection were most frequently VFRs (77%). The median trip duration was 31 days (interquartile range, 18 to 61 days), and 448 of 691 travelers (65%) had no pretravel consultation. Of 143 S Typhi and 75 S Paratyphi isolates for which there were susceptibility data, nonsusceptibility to antibiotics varied (fluoroquinolones, 65% and 56%, respectively; co-trimoxazole, 13% and 0%; macrolides, 8% and 16%). Two S Typhi isolates (1.5%) from India were nonsusceptible to third-generation cephalosporins. S Typhi fluoroquinolone nonsusceptibility was highest when infection was acquired in South Asia (70 of 90 isolates; 78%) and sub-Saharan Africa (6 of 10 isolates; 60%). Enteric fever is an important travel-associated illness complicated by AMR. Our data contribute to a better understanding of region-specific AMR, helping to inform empirical treatment options. Prevention measures need to focus on high-risk travelers including VFRs and children.

Forecasting Demand for the Typhoid Conjugate Vaccine in Low- and Middle-income Countries

BACKGROUND

The World Health Organization (WHO) released a position paper in March 2018 calling for integration of a novel typhoid conjugate vaccine (TCV) into routine immunization along with catch-up campaigns for children up to age 15. Gavi, the Vaccine Alliance, has committed funding to help resource-constrained countries introduce this vaccine. In this article, the Typhoid Vaccine Acceleration Consortium forecasts demand if WHO recommendations are followed.

METHODS

We built a model of global TCV introductions between 2020 and 2040 to estimate the demand of the vaccine for 133 countries. We estimated each country's year of introduction by examining its estimated incidence of typhoid fever, its history of introducing new vaccines, and any knowledge we have of its engagement with typhoid prevention, including intention to apply for Gavi funding. Our model predicted use in routine infant vaccination as well as campaigns targeting varying proportions of the unvaccinated population up to 15 years of age.

RESULTS

Between 2020 and 2025, demand will predominantly come from African countries, many receiving Gavi support. After that, Asian countries generate most demand until 2030, when campaigns are estimated to end. Demand will then track the birth cohort of participating countries, suggesting an annual routine demand between 90 and 100 million doses. Peak demand is likely to occur between 2023 and 2026, approaching 300 million annual doses if campaign implementation is high.

CONCLUSIONS

In our analysis, target population for catch-up campaigns is the main driver of uncertainty. At peak demand, there is some risk of exceeding presently estimated peak production capacity. Therefore, it will be important to carefully coordinate introductions, especially when accompanied by campaigns targeting large proportions of the eligible population.

Extensively Drug-Resistant (XDR) Typhoid: Evolution, Prevention, and Its Management

Typhoid fever is the result of a human host-restricted Salmonella enteric serotype typhi infection that causes enteric fever. Around 21 million people contract typhoid annually, with Pakistan's inhabitants at most risk amongst Asian countries where typhoid remains prevalent. Decades of indiscriminate antibiotic usage has driven the evolution of multidrug-resistant strains and more recently, extensively drug-resistant (XDR) strains of Salmonella enteric serotype typhi. Current reports of extensively drug-resistant typhoid fever outbreak in Pakistan are not only a major concern for Pakistan but also for health authorities worldwide: intercontinental transmission, spread, and replacement of native strains in neighboring countries and a major impediment to Pakistani health care management. The WHO records that there are 5274 cases of extensively drug-resistant (XDR) typhoid fever out of a total of 8188 total cases of typhoid fever reported in Pakistan. The last remaining feasible oral antibiotic that XDR typhoid remains susceptible to is azithromycin; this is a cause of major concern. Additionally, several cases of XDR typhoid fever have also been reported in patients travelling from Pakistan to the USA, UK, and Canada. This review article attempts to raise the issue of XDR typhoid with respect to its epidemiology, prevention, management, and future outlook and stresses a better understanding of antimicrobial stewardship and general surveillance of the disease. Although progress is being made to combat XDR typhoid locally, efficient, unified efforts on a national and international scale are required to contain the XDR outbreak before it is no longer manageable and leads us back to the preantibiotic era.

Travel-Related Typhoid Fever: Narrative Review of the Scientific Literature

Enteric fever is a foodborne infectious disease caused by Salmonella enterica serotypes Typhi and Paratyphi A, B and C. The high incidence in low income countries can increase the risk of disease in travelers coming from high income countries. Pre-travel health advice on hygiene and sanitation practices and vaccines can significantly reduce the risk of acquiring infections. Although the majority of the cases are self-limiting, life-threatening complications can occur. Delayed diagnosis and cases of infections caused by multi-drug resistant strains can complicate the clinical management and affect the prognosis. More international efforts are needed to reduce the burden of disease in low income countries, indirectly reducing the risk of travelers in endemic settings. Surveillance activities can help monitor the epidemiology of cases caused by drug-susceptible and resistant strains.

Azithromycin resistance mechanisms in typhoidal salmonellae in India: A 25 years analysis

Background & objectives

: Azithromycin has been in use as an alternate treatment option for enteric fever even when the guidelines on the susceptibility testing were not available. There is lack of data on susceptibility and mechanisms of resistance of azithromycin in Salmonella Typhi and S. Paratyphi A. The aim of the present study was to determine the azithromycin susceptibility and resistance mechanisms in typhoidal salmonellae isolates archived in a tertiary care centre in north India for a period of 25 years.

Methods

: Azithromycin susceptibility was determined in 602 isolates of S. Typhi (469) and S. Paratyphi A (133) available as archived collection isolated during 1993 to 2016, by disc diffusion and E-test method.PCR was done for ereA, ermA, ermB, ermC, mefA, mphA and msrA genes from plasmid and genomic DNA and sequencing was done to detect mutations in acrR, rplD and rplV genes.

Results

: Azithromycin susceptibility was seen in 437/469 [93.2%; 95% confidence interval (CI), 90.5 to 95.1%] isolates of S. Typhi. Amongst 133 isolates of S. Paratyphi A studied, minimum inhibitory concentration (MIC) of ≤16 mg/l was found in 102 (76.7%; 95% CI, 68.8 to 83.0). MIC value ranged between 1.5 and 32 mg/l with an increasing trend in MIC₅₀and MIC₉₀with time. Mutations were found in acrR in one and rplV in two isolates of S. Typhi. No acquired mechanism for macrolide resistance was found.

Interpretation & conclusions

: Azithromycin could be considered as a promising agent against typhoid fever on the basis of MIC distribution in India. However, due to emergence of resistance in some parts, there is a need for continuous surveillance of antimicrobial susceptibility and resistance mechanisms. There is also a need to determine the breakpoints for S. Paratyphi A.

Drug-resistant enteric fever worldwide, 1990 to 2018: a systematic review and meta-analysis

BACKGROUND

Antimicrobial resistance (AMR) is an increasing threat to global health. There are > 14 million cases of enteric fever every year and > 135,000 deaths. The disease is primarily controlled by antimicrobial treatment, but this is becoming increasingly difficult due to AMR. Our objectives were to assess the prevalence and geographic distribution of AMR in Salmonella enterica serovars Typhi and Paratyphi A infections globally, to evaluate the extent of the problem, and to facilitate the creation of geospatial maps of AMR prevalence to help targeted public health intervention.

METHODS

We performed a systematic review of the literature by searching seven databases for studies published between 1990 and 2018. We recategorised isolates to allow the analysis of fluoroquinolone resistance trends over the study period. The prevalence of multidrug resistance (MDR) and fluoroquinolone non-susceptibility (FQNS) in individual studies was illustrated by forest plots, and a random effects meta-analysis was performed, stratified by Global Burden of Disease (GBD) region and 5-year time period. Heterogeneity was assessed using the I2 statistics. We present a descriptive analysis of ceftriaxone and azithromycin resistance.

FINDINGS

We identified 4557 articles, of which 384, comprising 124,347 isolates (94,616 S. Typhi and 29,731 S. Paratyphi A) met the pre-specified inclusion criteria. The majority (276/384; 72%) of studies were from South Asia; 40 (10%) articles were identified from Sub-Saharan Africa. With the exception of MDR S. Typhi in South Asia, which declined between 1990 and 2018, and MDR S. Paratyphi A, which remained at low levels, resistance trends worsened for all antimicrobials in all regions. We identified several data gaps in Africa and the Middle East. Incomplete reporting of antimicrobial susceptibility testing (AST) and lack of quality assurance were identified.

INTERPRETATION

Drug-resistant enteric fever is widespread in low- and middle-income countries, and the situation is worsening. It is essential that public health and clinical measures, which include improvements in water quality and sanitation, the deployment of S. Typhi vaccination, and an informed choice of treatment are implemented. However, there is no licenced vaccine for S. Paratyphi A. The standardised reporting of AST data and rollout of external quality control assessment are urgently needed to facilitate evidence-based policy and practice.

TRIAL REGISTRATION

PROSPERO CRD42018029432.

Current antibiotic use in the treatment of enteric fever in children

Background & objectives

Antimicrobial resistance is a major challenge in the treatment of typhoid fever with limited choices left to empirically treat these patients. The present study was undertaken to determine the current practices of antibiotic use in children attending a tertiary care hospital in north India.

Methods

This was a descriptive observational study in children suffering from enteric fever as per the case definition including clinical and laboratory parameters. The antibiotic audit in hospitalized children was measured as days of therapy per 1000 patient days and in outpatient department (OPD) as antibiotic prescription on the treatment card.

Results

A total of 128 children with enteric fever were included in the study, of whom, 30 were hospitalized and 98 were treated from OPD. The mean duration of fever was 9.5 days at the time of presentation. Of these, 45 per cent were culture positive with Salmonella Typhi being aetiological agent in 68 per cent followed by S. Paratyphi A in 32 per cent. During hospitalization, the average length of stay was 10 days with mean duration of defervescence 6.4 days. Based on antimicrobial susceptibility ceftriaxone was given to 28 patients with mean duration of treatment being six days. An additional antibiotic was needed in six patients due to clinical non-response. In OPD, 79 patients were prescribed cefixime and additional antibiotic was needed in five during follow up visit.

Interpretation & conclusions

Based on our findings, ceftriaxone and cefixime seemed to be the first line of antibiotic treatment for typhoid fever. Despite susceptibility, clinical non-response was seen in around 10 per cent of the patients who needed combinations of antibiotics.

Typhoid and paratyphoid fever: a call to action

Purpose of review

Enteric fever remains a major global-health concern, estimated to be responsible for between 11.9 and 26.9 million cases annually. Long-term prevention of enteric fever will require improved access to safe drinking water combined with investment in sanitation and hygiene interventions. In the short-to-medium term, new control strategies for typhoid fever have arrived in the form of typhoid Vi-conjugate vaccines (TCVs), offering hope that disease control can be achieved in the near future.

Recent findings

The diagnosis of enteric fever is complicated by its nonspecific clinical presentation, coupled with the low sensitivity of commonly used diagnostics. Investment in diagnostics has the potential to improve management, to refine estimates of disease burden and to facilitate vaccine impact studies. A new generation of reliable, diagnostic tests is needed that are simultaneously accessible, cost-effective, sensitive, and specific. The emergence and global dissemination of multidrug-resistant, fluoroquinolone-resistant, and extensively drug-resistant (XDR) strains of Salmonella Typhi emphasizes the importance of continued surveillance and appropriate antibiotic stewardship, integrated into a global strategy to address antimicrobial resistance (AMR). Current empirical treatment guidelines are out of date and should be updated to respond to local trends in AMR, so as to guide treatment choices in the absence of robust diagnostics and laboratory facilities. In September 2017, the WHO Strategic Advisory Group of Experts (SAGE) immunization recommended the programmatic use of TCVs in high burden countries. Ongoing and future studies should aim to study the impact of these vaccines in a diverse range of setting and to support the deployment of TCVs in high-burden countries.

Summary

The advent of new generation TCVs offers us a practical and affordable public-health tool that – for the first time – can be integrated into routine childhood immunization programmes. In this review, we advocate for the deployment of TCVs in line with WHO recommendations, to improve child health and limit the spread of antibiotic-resistant S. Typhi.

Comparison of phenotypic and WGS-derived antimicrobial resistance profiles of Salmonella enterica serovars Typhi and Paratyphi

Objectives

Surveillance of antimicrobial resistance (AMR) in Salmonella enterica serovars Typhi and Paratyphi is essential to provide an evidence base for empirical treatment protocols and to monitor emerging AMR. We sought to compare phenotypic and WGS-based genotypic methods for the detection of AMR in Salmonella Typhi and Salmonella Paratyphi.

Methods

WGS data from 603 isolates of Salmonella Typhi (n = 332) and Salmonella Paratyphi (n = 271) were mapped to genes or chromosomal mutations known to be associated with phenotypic AMR and compared with phenotypic susceptibility data interpreted using breakpoints recommended by EUCAST.

Results

There were two (0.03%) discordant interpretations out of a possible 6030 isolate/antimicrobial class combinations. MDR (resistant to three or more classes of antimicrobial) was detected in 83/332 (25.0%) Salmonella Typhi isolates, but was not detected in Salmonella Paratyphi. Thirty-six (10.8%) isolates of Salmonella Typhi were resistant to ciprofloxacin (MIC >0.5 mg/L), with 33 (9.9%) of 332 exhibiting mutations in gyrA and parC, and 244 (73.5%) isolates had reduced susceptibility to ciprofloxacin (MIC 0.06-0.25 mg/L). In comparison, 209/227 (92.1%) isolates of Salmonella Paratyphi A exhibited resistance to ciprofloxacin (MIC >0.5 mg/L). No resistance to azithromycin or the third-generation cephalosporins was detected.

Conclusions

WGS data provided a robust and informative approach for monitoring MDR and emerging resistance to ciprofloxacin in Salmonella Typhi and Salmonella Paratyphi. Phenotypic antimicrobial susceptibility testing continues to be performed to guide targeted individual patient treatment, but inferred AMR profiles from WGS data may be used for surveillance and to guide empirical therapy.

Distribution and dissemination of antimicrobial-resistant Salmonella in broiler farms with or without enrofloxacin use

BACKGROUND

Salmonella is a major zoonotic food-borne pathogen that persists on poultry farms, and animals undergo reinfection with endemic strains. The present study aimed to investigate the characteristics and dissemination of antimicrobial-resistant Salmonella within and between broiler farms that used enrofloxacin and those that did not.

RESULTS

Cloacal and environmental (litter, feed, and water) samples from two selected flocks in each of 12 farms owned by the same company were collected three times over a 30-day period of two production cycles during 2015-2016. The rate of Salmonella isolation was 7.8% (123/1584). Nine Salmonella serotypes (116 isolates) and seven untypable isolates were identified, and Salmonella Montevideo was the most prevalent serotype. Azithromycin-resistant (17.9%) and colistin-resistant (3.3%) isolates were detected, and multidrug-resistant isolates (43.1%) were also observed. No isolate was resistant to enrofloxacin or ciprofloxacin; however, intermediate resistance to enrofloxacin was significantly higher (P < 0.05) in farms that used enrofloxacin than in those that did not. The rate of multi-drug resistance among litter isolates (25/44, 56.8%) was significantly higher (P < 0.05) than that among cloacal swab (24/67, 35.8%) and feed (4/12, 33.3%) isolates. Pulsed-field gel electrophoresis (PFGE) analysis of strains of the same serotype was conducted to determine their epidemiological relationship. The PFGE types were classified into 31 groups with a 100% correlation cutoff in dendrograms for Salmonella Montevideo isolates, which showed 100% genomic identity based on age, sample type, flock, and production cycle within and between farms.

CONCLUSION

The present study highlights the occurrence of horizontal transmission and cyclic contamination with antimicrobial-resistant Salmonella in broiler farms owned by the same company. Litter may be a good indicator of indoor environmental contamination with antimicrobial-resistant Salmonella on farms. Additionally, enrofloxacin use may be one of the factors promoting resistance towards it in Salmonella.

Travel and the Spread of Drug-Resistant Bacteria

PURPOSE OF REVIEW

The rise in antimicrobial resistance is an urgent public health threat which, in the absence of intervention, may result in a post-antibiotic era limiting the effectiveness of antibiotics to treat both common and serious infections. Globalization and human migration have profoundly contributed to the spread of drug-resistant bacteria. In this review, we summarize the recent literature on the importance of travelers in the spread of drug-resistant bacterial organisms. Our goal was to describe the importance of travel on a variety of clinically relevant drug-resistant bacterial organisms including extended-spectrum β-lactamase-producing Enterobacteriaceae, carbapenem-resistant Enterobacteriaceae, methicillin-resistant Staphylococcus aureus, Salmonella species, as well as other enteric infections.

RECENT FINDINGS

Travelers from high income countries, visiting low and middle income countries, frequently acquire drug-resistant bacteria, particularly extended-spectrum β-lactamase-producing Enterobacteriaceae. The highest risk is associated with travel to the Indian subcontinent. Multidrug-resistant enteric infections in travelers from Salmonella spp., Campylobacter spp., and Shigella spp. are increasing. Refugees, pilgrimages, and medical tourists are associated with considerable risk of multiple forms of drug resistance. This review highlights the importance of antimicrobial stewardship, infection control, and surveillance; particularly in low and middle income countries. International leadership with global coordination is vital in the battle against antimicrobial resistance.

Typhoid Fever due to Extended Spectrum β-Lactamase-Producing Salmonella enterica Serovar Typhi: A Case Report and Literature Review

Emergence of cephalosporin-resistant strains of Salmonella enterica serovar Typhi is a cause of concern in the management of enteric fever. Cephalosporin resistance in Salmonella species is mainly due to the production of extended-spectrum β-lactamases (ESBLs). The majority of ESBLs in Salmonella enterica serovar Typhi are derivatives of the TEM, SHV, and CTX-M β-lactamase families. Of these, CTX-M appears to be predominant. This paper discusses the detection and molecular characterization of an ESBL-producing Salmonella enterica serovar Typhi strain isolated from a patient who was admitted to a private hospital in Sri Lanka. The three main types of β-lactamases such as TEM, SHV, and CTX-M were identified in this isolate. This case report from Sri Lanka contributes to the knowledge of the increasingly reported cases of typhoid fever due to Salmonella enterica serovar Typhi resistant to β-lactamase by ESBL production.

Enteric fever among children: 50 cases in a French tertiary care centre

BACKGROUND

Enteric fever in France is primarily travel-associated. Characteristics of paediatric cases are scarce and information from field studies in endemic countries might not be generalizable to non-endemic countries.

METHODS

In this retrospective study, we reviewed all cases of typhoid and paratyphoid fever treated in a French paediatric tertiary care centre from 1993 to 2015.

RESULTS

Fifty cases of enteric fever due to Salmonella enterica serovar Typhi (n = 44) and Paratyphi (n = 6) were identified. Sixty-one percent of the children had travelled to Africa and 34% to the Indian subcontinent. Among travel-associated cases, 85% were visiting friends and relatives (VFR). Ninety-six percent had high fever associated with gastrointestinal symptoms. Anaemia (66%), elevated C-reactive protein (80%), transaminitis (87%) and mild hyponatremia (50%) were the main biological findings. Blood cultures were positive in 90% of cases. Twelve strains (24%) were resistant at least to one antibiotic, and all of them had been isolated since 2003, increasing the resistance rate during this last period to 43% (12/28). Ceftriaxone was administered to 71 patients for a median duration of 6 days (interquartile range (IQR): 4-8). The median time to apyrexia after the onset of treatment was 4 days (IQR: 2-5 days). Complications occurred in nine children with five (10%) presenting neurologic disorders. All 50 patients recovered.

CONCLUSION

In France, paediatric enteric fever is mainly a travel-associated disease and occurs in patients returning from a prolonged stay in an endemic area. Children VFR are at high risk and should be a priority target group for pre-travel preventive measures. The increase in antibiotic resistance reflects the situation in endemic countries and is a major concern.

The evolution of antimicrobial resistance in Salmonella Typhi

PURPOSE OF REVIEW

Increasing antimicrobial resistance in Salmonella Typhi is a serious public health concern, especially in industrializing countries. Here we review recent clinical and laboratory data concerning the evolution of antimicrobial resistance, with particular reference to the emergence resistance against fluoroquinolones, third generation cephalosporins, and azithromycin.

RECENT FINDINGS

The last 40 years have witnessed the sequential emergence of resistance to all first-line antimicrobials used in the treatment of S. Typhi infections. Multidrug resistance (MDR), defined by resistance to chloramphenicol, amoxicillin, and co-trimoxazole, emerged in the 1990s, followed rapidly by reduced susceptibility to fluoroquinolones. In the current decade, high-level fluoroquinolone resistance has emerged in south Asia and threatens to spread worldwide. Increasing reliance is now being placed on the activity of third generation cephalosporins and azithromycin, but resistance against these agents is developing. Carbapenems and tigecycline may be alternatives, although clinical data are sparse, and in some settings reversion to chloramphenicol and co-trimoxazole susceptibility is occurring. Therefore, older drugs may yet have a role in the treatment of S. Typhi infections.

SUMMARY

Good surveillance, improved diagnostics, more prudent use of antimicrobials, and effective vaccines will all be critical to reducing the burden of disease caused by S. Typhi.

Interaction of Antibiotics with Innate Host Defense Factors against Salmonella enterica Serotype Newport

It is becoming increasingly understood that the current paradigms of in vitro antimicrobial susceptibility testing may have significant shortcomings in predicting activity in vivo. This study evaluated the activity of several antibiotics alone and in combination against clinical isolates of Salmonella enterica serotype Newport (meningitis case) utilizing both conventional and physiological media. In addition, the interactions of these antibiotics with components of the innate immune system were evaluated. Azithromycin, which has performed quite well clinically despite high MICs in conventional media, was shown to be more active in physiological media and to enhance innate immune system killing. Alternatively, chloramphenicol did not show enhanced immune system killing, paralleling its inferior clinical performance to other antibiotics that have been used to treat Salmonella meningitis. These findings are important additions to the building understanding of current in vitro antimicrobial assay limitations that hopefully will amount to future improvements in these assays to better predict clinical efficacy and activity in vivo.

This study examines the pharmacodynamics of antimicrobials that are used to treat Salmonella with each other and with key components of the innate immune system. Antimicrobial synergy was assessed using time-kill and checkerboard assays. Antimicrobial interactions with innate immunity were studied by employing cathelicidin LL-37, whole-blood, and neutrophil killing assays. Ceftriaxone and ciprofloxacin were found to be synergistic in vitro against Salmonella enterica serotype Newport. Ceftriaxone, ciprofloxacin, and azithromycin each demonstrated synergy with the human cathelicidin defense peptide LL-37 in killing Salmonella. Exposure of Salmonella to sub-MICs of ceftriaxone resulted in enhanced susceptibility to LL-37, whole blood, and neutrophil killing. The activity of antibiotics in vivo against Salmonella may be underestimated in bacteriologic media lacking components of innate immunity. The pharmacodynamic interactions of antibiotics used to treat Salmonella with each other and with components of innate immunity warrant further study in light of recent findings showing in vivo selection of antimicrobial resistance by single agents in this pathogen.

IMPORTANCE It is becoming increasingly understood that the current paradigms of in vitro antimicrobial susceptibility testing may have significant shortcomings in predicting activity in vivo. This study evaluated the activity of several antibiotics alone and in combination against clinical isolates of Salmonella enterica serotype Newport (meningitis case) utilizing both conventional and physiological media. In addition, the interactions of these antibiotics with components of the innate immune system were evaluated. Azithromycin, which has performed quite well clinically despite high MICs in conventional media, was shown to be more active in physiological media and to enhance innate immune system killing. Alternatively, chloramphenicol did not show enhanced immune system killing, paralleling its inferior clinical performance to other antibiotics that have been used to treat Salmonella meningitis. These findings are important additions to the building understanding of current in vitro antimicrobial assay limitations that hopefully will amount to future improvements in these assays to better predict clinical efficacy and activity in vivo.

The clinical and microbiological characteristics of enteric fever in Cambodia, 2008-2015

BACKGROUND

Enteric fever remains a major public health problem in low resource settings and antibiotic resistance is increasing. In Asia, an increasing proportion of infections is caused by Salmonella enterica serovar Paratyphi A, which for a long time was assumed to cause a milder clinical syndrome compared to Salmonella enterica serovar Typhi.

METHODOLOGY

A retrospective chart review study was conducted of 254 unique cases of blood culture confirmed enteric fever who presented at a referral adult hospital in Phnom Penh, Cambodia between 2008 and 2015. Demographic, clinical and laboratory data were collected from clinical charts and antibiotic susceptibility testing was performed. Whole genome sequence analysis was performed on a subset of 121 isolates.

RESULTS

One-hundred-and-ninety unique patients were diagnosed with Salmonella Paratyphi A and 64 with Salmonella Typhi. In the period 2008-2012, Salmonella Paratyphi A comprised 25.5% of 47 enteric fever cases compared to 86.0% of 207 cases during 2013-2015. Presenting symptoms were identical for both serovars but higher median leukocyte counts (6.8 x 109/L vs. 6.3 x 109/L; p = 0.035) and C-reactive protein (CRP) values (47.0 mg/L vs. 36 mg/L; p = 0.034) were observed for Salmonella Typhi infections. All but one of the Salmonella Typhi isolates belonged to haplotype H58 associated with multidrug resistance (MDR) (i.e. resistance to ampicillin, chloramphenicol and co-trimoxazole).;42.9% actually displayed MDR compared to none of the Salmonella Paratyphi A isolates. Decreased ciprofloxacin susceptibility (DCS) was observed in 96.9% (62/64) of Salmonella Typhi isolates versus 11.5% (21/183) of Salmonella Paratyphi A isolates (all but one from 2015). All isolates were susceptible to azithromycin and ceftriaxone.

CONCLUSIONS

In Phnom Penh, Cambodia, Salmonella Paratyphi A now causes the majority of enteric fever cases and decreased susceptibility against ciprofloxacin is increasing. Overall, Salmonella Typhi was significantly more associated with MDR and DCS compared to Salmonella Paratyphi A.

Renaissance of Conventional First-Line Antibiotics in Salmonella enterica Clinical Isolates: Assessment of MICs for Therapeutic Antimicrobials in Enteric Fever Cases from Nepal

Enteric fever caused by Salmonella enterica is a life-threatening systemic illness of gastrointestinal tract especially in tropical countries. Antimicrobial therapy is generally indicated but resistance towards commonly used antibiotics has limited their therapeutic usefulness. Therefore, we aimed to determine the antimicrobial susceptibility pattern by minimum inhibitory concentration method of common therapeutic regimens against Salmonella enterica from enteric fever clinical cases. Salmonella enterica clinical isolates recovered from the patients with suspected enteric fever whose blood samples were submitted to microbiology laboratory of Manmohan Memorial Community Hospital, Kathmandu, from March 2016 to August 2016, were studied. These isolates were subjected to antimicrobial susceptibility testing against common therapeutic antimicrobials by Kirby-Bauer disk diffusion method. The minimum inhibitory concentration of ciprofloxacin, azithromycin, chloramphenicol, and cefixime was determined by Agar dilution method based on the latest CLSI protocol. A total of 88 isolates of Salmonella enterica were recovered from blood samples of enteric fever cases. Out of them, 74 (84.09%) were Salmonella Typhi and 14 (15.91%) were Salmonella Paratyphi A. On Kirby-Bauer disk diffusion antimicrobial susceptibility testing, entire isolates were susceptible to cotrimoxazole, cefixime, ceftriaxone, azithromycin, and chloramphenicol. Sixty-four (72.7%) Salmonella enterica isolates were nalidixic acid resistant and nonsusceptible to ciprofloxacin and levofloxacin. On MIC determination, four Salmonella isolates were ciprofloxacin resistant with MIC 1 µg/ml and two isolates were ciprofloxacin intermediate with MIC 0.5 µg/ml. The MIC range of azithromycin was from 0.125 µg/ml to 2.0 µg/ml, whereas that for chloramphenicol was 2.0 µg/ml–8.0 µg/ml and for cefixime was 0.0075–0.5 µg/ml, respectively. Despite global surge of antimicrobial resistance among Salmonella enterica clinical isolates, the level of drug resistance in our study was not so high. However, higher level of NARST strains limits therapeutic use of fluoroquinolones and necessitates the routine monitoring of such resistance determinants in order to effectively and rationally manage enteric fever cases.

Isolation of multidrug-resistant Salmonella in Singapore

Multidrug-resistant Salmonella is a well-recognised problem worldwide, especially in developing countries such as India, where non-typhoidal Salmonella infections and enteric fever are endemic. Antimicrobial resistance, particularly to fluoroquinolones, is common and leads to the frequent use of alternative agents, such as azithromycin. We herein describe the first reported case of azithromycin-resistant Salmonella gastroenteritis in a Singaporean patient.

Antimicrobial susceptibility to azithromycin among Salmonella enterica Typhi and Paratyphi A isolates from India

Decreased ciprofloxacin susceptibility (DCS) and multidrug resistance in typhoidal Salmonella isolates in areas of endemicity are significant therapeutic problems. Guidelines for azithromycin disc diffusion and MIC interpretive criteria for Salmonella enterica serovar Typhi were published recently by the Clinical and Laboratory Standards Institute in 2015. We investigated the antimicrobial susceptibility pattern of azithromycin in 100 isolates of Salmonella Typhi (n=80), Paratyphi A (n=18) and B (n=2) recovered from bloodstream infections from January 2013 to December 2015. Zone sizes were extrapolated against MIC values, and a scatter plot was constructed. The azithromycin MICs by Etest ranged from 2 to 16 µg ml-1, while the disc diffusion diameters were from 13 to 22 mm. We observed that the margin of the zone of inhibition around the azithromycin disc may not be very clear and therefore difficult to interpret and that there was wide variation in the zone sizes for the same MIC value in both serovars. DCS was observed in 85 % of Salmonella Typhi recovered (68/80) and in 15/18 (83.3 %) Paratyphi A isolates. Judicious use of azithromycin is advocated as an alternative oral agent in endemic areas where DCS is common.

Antimicrobial resistance and molecular subtypes of Salmonella enterica serovar Typhi isolates from Kolkata, India over a 15 years period 1998-2012

Typhoid fever, caused by Salmonella enterica serovar Typhi (S. Typhi), remains an unresolved public health problem in India. Emergence of antimicrobial resistant strains poses a great concern for typhoid treatment and influences reshaping of current S. Typhi population. We included representative S. Typhi strains (n=164) from retrospective studies, both community and hospital based, conducted at National Institute of Cholera and Enteric Diseases, Kolkata during 15 years period (1998-2012) to analyze their antimicrobial resistance (AMR) profiles, mechanism of AMR and molecular subtypes of the strains. More than 60% of the S. Typhi isolates were obtained from community based studies. During the study period, steady decline (46.4%-15.6%) in isolation of multidrug-resistant (MDR, resistant to ampicillin, chloramphenicol and co-trimoxazole) S. Typhi was noticed with parallel increase of nalidixic acid-resistant (NAL^R) strains (60.7%-93.8%) and ciprofloxacin resistant (CIP^R) strains (0%-25%). Of 53 MDR strains, 46 (86.8%) were NAL^R showing decreased ciprofloxacin susceptible (DCS) (MIC for ciprofloxacin 0.12-0.5μg/ml) phenotype. Conjugative IncHI1 (230kb) and non-conjugative non-IncHI1 (180kb) plasmids were found in 23 (43.4%) and 14 (26.4%) MDR strains respectively, plasmid was absent in 16 (30.2%) MDR strains. MDR strains with or without plasmid shared the same set of resistance genes (bla_TEM-1, catA1, sul1, sul2, strA and strB) and class 1 integron possessing dfrA7 gene cassette. Two S. Typhi strains harbored 50kb transferrable plasmids carrying dfrA15 and aadA1 gene cassettes in class 1 integron. The majority of the strains (135/164, 82.3%) belonged to H58 haplotype. Among the MDR isolates, fluoroquinolone resistant or combined resistant isolates (n=147), 127 (86.4%) were H58 and 20 (13.6%) belonged to non-H58. NAL^RS. Typhi strains with decreased susceptibility or resistance to ciprofloxacin had point mutation(s) in quinolone resistance-determining region of gyrA and parC genes. Pulsed-field gel electrophoresis showed more diversity among NAL^RS. Typhi than MDR strains. Results of this study generated information useful for better understanding of the disease epidemiology and its control in endemic settings.

A case of clinical and microbiological failure of azithromycin therapy in Salmonella enterica serotype Typhi despite low azithromycin MIC

Typhoid fever remains a serious problem in many developing countries. Due to resistance to multiple first line drugs, azithromycin has evolved as an important drug in the treatment of typhoid. While therapy with azithromycin is highly effective, no clinically validated mean inhibitory concentration (MIC) break points or disc diffusion cutoff guidelines are available so far. We describe an Indian adult with clinical and microbiological failure to azithromycin despite low azithromycin MIC.

Revisit of fluoroquinolone and azithromycin susceptibility breakpoints for Salmonella enterica serovar Typhi

In recent years, increase in occurrence of fluoroquinolone (FQ)-resistant S almonella Typhi isolates has caused considerable inconvenience in selecting appropriate antimicrobials for treatment of typhoid. The World Health Organization (WHO) recommends azithromycin for the empirical treatment option of uncomplicated typhoid. The CLSI updated the breakpoints of disc diffusion (DD) and MIC results of FQs and azithromycin for Salmonella Typhi in 2015, but DD breakpoints of ofloxacin and levofloxacin were not included. In this study, the inhibition zone diameters and MICs of nalidixic acid, ciprofloxacin, ofloxacin, levofloxacin and azithromycin were determined in Salmonella Typhi Kolkata isolates (n =146) over a 16-year period (1998 to 2013) and the data were compared with the available CLSI breakpoints. Very major error and major error (ME) of FQs were not observed in the study isolates, but the minor error of ciprofloxacin (15.8 %) and ME of azithromycin (3.5 %) exceeded the acceptable limit. A positive correlation between MICs of FQ and mutations in the quinolone-resistance-determining region (QRDR) showed the reliability of MIC results to determine FQ susceptibility of Salmonella Typhi (n =74). Isolates showing decreased ciprofloxacin susceptibility (MIC 0.125-0.5 µg  ml-1) were likely to have at least one mutation in the QRDR region. The results on DD breakpoints of ofloxacin (resistant, ≤15 mm; intermediate, 16-24 mm, and susceptible, ≥25 mm) and levofloxacin (resistant, ≤18 mm; intermediate, 19-27 mm, and susceptible, ≥28 mm) corroborated those of earlier studies. In view of the emerging FQ- and azithromycin-resistant Salmonella Typhi isolates, DD and MIC breakpoints of those antimicrobials should be revisited routinely.

Case Series of Imported Enteric Fever at a Referral Center in Tokyo, Japan: Antibiotic Susceptibility and Risk Factors for Relapse

Owing to the increase in Salmonella strains with decreased fluoroquinolone susceptibility in the endemic areas, we have been treating enteric fever with intravenous ceftriaxone empirically since 2007. In this study, we reevaluated our treatment protocol. This retrospective cohort study was conducted at a single institute in Tokyo, Japan, between January 2006 and December 2013. Enteric fever was defined as isolation of Salmonella Typhi or Salmonella Paratyphi A, B, and C from the blood and/or stool of patients with fever. Of the 35 patients with imported enteric fever, 28 (80%) had returned from south Asia. Ciprofloxacin-susceptible strains were detected in only 12% of the cases. The isolates showed excellent susceptibility to ampicillin (91%), chloramphenicol (94%), ceftriaxone (97%), and azithromycin (97%). One case of Salmonella Paratyphi B was excluded, and of the remaining 34 patients, 56% were treated with ceftriaxone alone, 26% with ceftriaxone then fluoroquinolone, and 9% with levofloxacin alone. The overall relapse rate was 6.1%; however, among those receiving ceftriaxone monotherapy, the relapse rate was 11% (N = 2). The relapse group was characterized by longer times to treatment initiation (P = 0.035) and defervescence (> 7 days) after treatment initiation (P = 0.022). In such cases, we recommend that ceftriaxone treatment be continued for > 4 days after defervescence or be changed to fluoroquinolone if the strains are found to be susceptible to prevent relapse. Furthermore, ampicillin and chloramphenicol, which are no longer prescribed, may be reconsidered as treatment options in Asia.

Detection of amino acid substitutions in the GyrA protein of fluoroquinolone-resistant typhoidal Salmonella isolates using high-resolution mass spectrometry

Infections with typhoidal Salmonella isolates that are resistant to fluoroquinolone antibiotics have become very common in several Asian countries. In the majority of these cases, resistance to fluoroquinolone-based antibiotics is associated with genetic mutations in the quinolone resistance-determining region (QRDR) of the bacterial DNA gyrase gene gyrA. The objective of this study was to detect these amino acid substitutions by high-resolution mass spectrometry instead of sequencing of the gyrA gene. A liquid chromatography-mass spectrometry (LC-MS) methodology was developed and evaluated for the detection of amino acid substitutions in the GyrA protein of 23 typhoidal Salmonella isolates. These isolates included typhoidal Salmonella that possessed different antibiotic sensitivities to fluoroquinolone antibiotics. The LC-MS methodology correctly identified peptide sequences associated with phenotypic QRDR mutations of the GyrA protein in all 23 phenotypically diverse typhoidal Salmonella isolates tested. In conclusion, a reliable and rapid LC-MS methodology has been developed that is able to identify GyrA QRDR mutations that are involved in the development of fluoroquinolone resistance in typhoidal Salmonella spp. Furthermore, this 'proof of principle' study indicates the potential usefulness of LC-MS in future detection of antibiotic resistance.

Epidemiology, Clinical Presentation, Laboratory Diagnosis, Antimicrobial Resistance, and Antimicrobial Management of Invasive Salmonella Infections

Salmonella enterica infections are common causes of bloodstream infection in low-resource areas, where they may be difficult to distinguish from other febrile illnesses and may be associated with a high case fatality ratio. Microbiologic culture of blood or bone marrow remains the mainstay of laboratory diagnosis. Antimicrobial resistance has emerged in Salmonella enterica, initially to the traditional first-line drugs chloramphenicol, ampicillin, and trimethoprim-sulfamethoxazole. Decreased fluoroquinolone susceptibility and then fluoroquinolone resistance have developed in association with chromosomal mutations in the quinolone resistance-determining region of genes encoding DNA gyrase and topoisomerase IV and also by plasmid-mediated resistance mechanisms. Resistance to extended-spectrum cephalosporins has occurred more often in nontyphoidal than in typhoidal Salmonella strains. Azithromycin is effective for the management of uncomplicated typhoid fever and may serve as an alternative oral drug in areas where fluoroquinolone resistance is common. In 2013, CLSI lowered the ciprofloxacin susceptibility breakpoints to account for accumulating clinical, microbiologic, and pharmacokinetic-pharmacodynamic data suggesting that revision was needed for contemporary invasive Salmonella infections. Newly established CLSI guidelines for azithromycin and Salmonella enterica serovar Typhi were published in CLSI document M100 in 2015.

Antimicrobial resistance and management of invasive Salmonella disease

Invasive Salmonella infections (typhoidal and non-typhoidal) cause a huge burden of illness estimated at nearly 3.4 million cases and over 600,000 deaths annually especially in resource-limited settings. Invasive non-typhoidal Salmonella (iNTS) infections are particularly important in immunosuppressed populations especially in sub-Saharan Africa, causing a mortality of 20-30% in vulnerable children below 5 years of age. In these settings, where routine surveillance for antimicrobial resistance is rare or non-existent, reports of 50-75% multidrug resistance (MDR) in NTS are common, including strains of NTS also resistant to flouroquinolones and 3rd generation cephalosporins. Typhoid (enteric) fever caused by Salmonella Typhi and Salmonella Paratyphi A remains a major public health problem in many parts of Asia and Africa. Currently over a third of isolates in many endemic areas are MDR, and diminished susceptibility or resistance to fluoroquinolones, the drugs of choice for MDR cases over the last decade is an increasing problem. The situation is particularly worrying in resource-limited settings where the few remaining effective antimicrobials are either unavailable or altogether too expensive to be afforded by either the general public or by public health services. Although the prudent use of effective antimicrobials, improved hygiene and sanitation and the discovery of new antimicrobial agents may offer hope for the management of invasive salmonella infections, it is essential to consider other interventions including the wider use of WHO recommended typhoid vaccines and the acceleration of trials for novel iNTS vaccines. The main objective of this review is to describe existing data on the prevalence and epidemiology of antimicrobial resistant invasive Salmonella infections and how this affects the management of these infections, especially in endemic developing countries.

Clinically and microbiologically derived azithromycin susceptibility breakpoints for Salmonella enterica serovars Typhi and Paratyphi A

Azithromycin is an effective treatment for uncomplicated infections with Salmonella enterica serovar Typhi and serovar Paratyphi A (enteric fever), but there are no clinically validated MIC and disk zone size interpretative guidelines. We studied individual patient data from three randomized controlled trials (RCTs) of antimicrobial treatment in enteric fever in Vietnam, with azithromycin used in one treatment arm, to determine the relationship between azithromycin treatment response and the azithromycin MIC of the infecting isolate. We additionally compared the azithromycin MIC and the disk susceptibility zone sizes of 1,640 S. Typhi and S. Paratyphi A clinical isolates collected from seven Asian countries. In the RCTs, 214 patients who were treated with azithromycin at a dose of 10 to 20 mg/ml for 5 to 7 days were analyzed. Treatment was successful in 195 of 214 (91%) patients, with no significant difference in response (cure rate, fever clearance time) with MICs ranging from 4 to 16 μg/ml. The proportion of Asian enteric fever isolates with an MIC of ≤ 16 μg/ml was 1,452/1,460 (99.5%; 95% confidence interval [CI], 98.9 to 99.7) for S. Typhi and 207/240 (86.3%; 95% CI, 81.2 to 90.3) (P < 0.001) for S. Paratyphi A. A zone size of ≥ 13 mm to a 5-μg azithromycin disk identified S. Typhi isolates with an MIC of ≤ 16 μg/ml with a sensitivity of 99.7%. An azithromycin MIC of ≤ 16 μg/ml or disk inhibition zone size of ≥ 13 mm enabled the detection of susceptible S. Typhi isolates that respond to azithromycin treatment. Further work is needed to define the response to treatment in S. Typhi isolates with an azithromycin MIC of >16 μg/ml and to determine MIC and disk breakpoints for S. Paratyphi A.

Trends in serotype distribution and antimicrobial susceptibility in Salmonella enterica isolates from humans in Belgium, 2009 to 2013

The Belgian National Reference Centre for Salmonella received 16,544 human isolates of Salmonella enterica between January 2009 and December 2013. Although 377 different serotypes were identified, the landscape is dominated by S. enterica serovars Typhimurium (55%) and Enteritidis (19%) in a ratio which is inverse to European Union averages. With outbreaks of Salmonella serotypes Ohio, Stanley, and Paratyphi B variant Java as prime examples, 20 serotypes displayed significant fluctuations in this 5-year period. Typhoid strains account for 1.2% of Belgian salmonellosis cases. Large-scale antibiotic susceptibility analyses (n = 4,561; panel of 12 antibiotics) showed declining resistance levels in S. Enteritis and Typhimurium isolates for 8 and 3 tested agents, respectively. Despite low overall resistance to ciprofloxacin (4.4%) and cefotaxime (1.6%), we identified clonal lineages of Salmonella serotypes Kentucky and Infantis displaying rising resistance against these clinically important drugs. Quinolone resistance is mainly mediated by serotype-specific mutations in GyrA residues Ser83 and Asp87 (92.2% not wild type), while an additional ParC_Ser80Ile mutation leads to ciprofloxacin resistance in 95.5% S. Kentucky isolates, which exceeds European averages. Plasmid-mediated quinolone resistance (PMQR) alleles qnrA1 (n = 1), qnrS (n = 9), qnrD1 (n = 4), and qnrB (n = 4) were found in only 3.0% of 533 isolates resistant to nalidixic acid. In cefotaxime-resistant isolates, we identified a broad range of Ambler class A and C β-lactamase genes (e.g., bla(SHV-12), blaTEM-52, bla(CTX-M-14), and bla(CTX-M-15)) commonly associated with members of the family Enterobacteriaceae. In conclusion, resistance to fluoroquinolones and cefotaxime remains rare in human S. enterica, but clonal resistant serotypes arise, and continued (inter)national surveillance is mandatory to understand the origin and routes of dissemination thereof.

Case report: failure under azithromycin treatment in a case of bacteremia due to Salmonella enterica Paratyphi A

Background

Limited information is available regarding the clinical efficacy of azithromycin for the treatment of enteric fever due to fluoroquinolone-resistant Salmonella Typhi and Salmonella Paratyphi among travelers returning to their home countries.

Case presentation

We report a case of a 52-year-old Japanese man who returned from India, who developed a fever of 39°C with no accompanying symptoms 10 days after returning to Japan from a 1-month business trip to Delhi, India. His blood culture results were positive for Salmonella Paratyphi A. He was treated with 14 days of ceftriaxone, after which he remained afebrile for 18 days before his body temperature again rose to 39°C with no apparent symptoms. He was then empirically given 500 mg of azithromycin, but experienced clinical and microbiological failure of azithromycin treatment for enteric fever due to Salmonella Paratyphi A. However, the minimum inhibitory concentration (MIC) of azithromycin was not elevated (8 mg/L). He was again given ceftriaxone for 14 days with no signs of recurrence during the follow-up.

Conclusion

There are limited data available for the treatment of enteric fever using azithromycin in travelers from developed countries who are not immune to the disease, and thus, careful follow-up is necessary. In our case, the low azithromycin dose might have contributed the treatment failure. Additional clinical data are needed to determine the rate of success, MIC, and contributing factors for success and/or failure of azithromycin treatment for both Salmonella Typhi and Salmonella Paratyphi infections.