Characterization of norovirus-associated traveler's diarrhea

Bacterial, viral and parasitic pathogens analysed by qPCR: Findings from a prospective study of travellers' diarrhoea

BACKGROUND

The diagnostics of travellers' diarrhoea (TD) has been revolutionised by multiplex qPCR assays. While mostly of bacterial aetiology, viruses and parasites account for the disease among 10-20% of travellers. Despite this, prospective studies applying qPCR assays remain scarce that cover not only bacteria, such as the various diarrhoeagenic Escherichia coli (DEC), but also viral and parasitic pathogens.

METHOD

We analysed by qPCR pre- and post-travel stool samples of 146 Finnish travellers for bacterial, viral and parasitic pathogens: enteropathogenic (EPEC), enteroaggregative (EAEC), enterotoxigenic (ETEC), enterohaemorrhagic (EHEC), and enteroinvasive (EIEC) E. coli; Shigella, Campylobacter, Salmonella, Yersinia and Vibrio cholerae; norovirus G1 and G2, rotavirus, enteroviruses, and sapovirus; and Giardia lamblia, Entamoeba histolytica, and Cryptosporidium. Symptoms and medication data during travel were collected by questionnaires.

RESULTS

We detected bacterial pathogens in 102/146 samples (69.9%; EAEC, EPEC, ETEC most common), viral ones in 13 (8.9%; norovirus most common), and parasitic ones in one (0.7%; Giardia). Noroviruses were associated with severe symptoms (23.5% versus non-severe 4.9%). In the TD group, 41.7% (5/12) of those with viral pathogens (vs. 13.3%; 11/83 without) took antibiotics.

CONCLUSION

Viral pathogens, particularly noroviruses, prevail in severe TD. The symptoms of viral disease are often severe and lead to unwarranted use of antibiotics.

Human Norovirus Proteins: Implications in the Replicative Cycle, Pathogenesis, and the Host Immune Response

Human noroviruses (HuNoVs) are the cause of more than 95% of epidemic non-bacterial gastroenteritis worldwide, with some lethal cases. These viral agents affect people of all ages. However, young children and older adults are the highest-risk groups, being affected with the greatest rate of hospitalizations and morbidity cases. HuNoV structural proteins, especially VP1, have been studied extensively. In contrast, the functions of the non-structural proteins of the virus have been undescribed in depth. Studies on HuNoV non-structural proteins have mostly been made by expressing them individually in in vitro cultures, providing insights of their functions and the role that they play in HuNoV replication and pathogenesis. This review examines exhaustively the functions of both HuNoV structural and non-structural proteins and their possible role within the viral replicative cycle and the pathogenesis of the virus. It also highlights recent findings regarding the host's innate and adaptive immune responses against HuNoV, which are of great relevance for diagnostics and vaccine development so as to prevent infections caused by these fastidious viruses.

Estimating the incidence of norovirus acute gastroenteritis among US and European international travelers to areas of moderate to high risk of traveler's diarrhea: a prospective cohort study protocol

Background

Acute gastroenteritis (AGE) is the leading cause of illness among returning travelers seeking medical care. Multiple types of enteric pathogens can cause travel-acquired AGE and, while bacterial pathogens have a predominant role, the importance of viruses, such as norovirus, is increasingly recognized. There is a lack of information on travel-acquired norovirus incidence among symptomatic and asymptomatic individuals irrespective of healthcare-seeking behavior. Our aim is to estimate the incidence of travel-acquired AGE due to norovirus and to characterize the burden of disease among international travelers from the United States and Europe.

Methods

We describe a prospective cohort study implemented in five US and European sites to estimate the role of AGE due to norovirus among adult international travelers. We enrolled individuals aged 18 years and older who are traveling to regions of moderate-high risk of AGE, or via cruise ship with an international port stop, with a trip duration of 3–15 days. The study will generate a wide range of health and travel-related data for pre-, during, and up to 6-months post-travel. We will identify laboratory-confirmed travel-acquired norovirus infections among both symptomatic and asymptomatic individuals from self-collected whole stool samples tested via quantitative RT-PCR. Coinfections will be identified in a subset of travelers with AGE using a multiplex molecular-based assay.

Discussion

This study is unique in design and breadth of data collected. The prospective collection of health and behavioral data, as well as biologic samples from travelers irrespective of symptoms, will provide useful data to better understand the importance of norovirus AGE among international travelers. This study will provide data to estimate the incidence of norovirus infections and AGE and the risk of post-infectious sequelae in the 6-month post-travel period serving as a baseline for future norovirus AGE vaccination studies. This study will contribute valuable information to better understand the role of norovirus in travel-acquired AGE risk and the impact of these infections on a broad set of outcomes.

Visualization-assisted binning of metagenome assemblies reveals potential new pathogenic profiles in idiopathic travelers' diarrhea

BACKGROUND

Travelers' diarrhea (TD) is often caused by enterotoxigenic Escherichia coli, enteroaggregative E. coli, other bacterial pathogens, Norovirus, and occasionally parasites. Nevertheless, standard diagnostic methods fail to identify pathogens in more than 40% of TD patients. It is predicted that new pathogens may be causative agents of the disease.

RESULTS

We performed a comprehensive amplicon and whole genome shotgun (WGS) metagenomic study of the fecal microbiomes from 23 TD patients and seven healthy travelers, all of which were negative for the known etiologic agents of TD based on standard microbiological and immunological assays. Abnormal and diverse taxonomic profiles in TD samples were revealed. WGS reads were assembled and the resulting contigs were visualized using multiple query types. A semi-manual workflow was applied to isolate independent genomes from metagenomic pools. A total of 565 genome bins were extracted, 320 of which were complete enough to be characterized as cellular genomes; 160 were viral genomes. We made predictions of the etiology of disease for many of the individual subjects based on the properties and features of the recovered genomes. Multiple patients with low-diversity metagenomes were predominated by one to several E. coli strains. Functional annotation allowed prediction of pathogenic type in many cases. Five patients were co-infected with E. coli and other members of Enterobacteriaceae, including Enterobacter, Klebsiella, and Citrobacter; these may represent blooms of organisms that appear following secretory diarrhea. New "dark matter" microbes were observed in multiple samples. In one, we identified a novel TM7 genome that phylogenetically clustered with a sludge isolate; it carries genes encoding potential virulence factors. In multiple samples, we observed high proportions of putative novel viral genomes, some of which form clusters with the ubiquitous gut virus, crAssphage. The total relative abundance of viruses was significantly higher in healthy travelers versus TD patients.

CONCLUSION

Our study highlights the strength of assembly-based metagenomics, especially the manually curated, visualization-assisted binning of contigs, in resolving unusual and under-characterized pathogenic profiles of human-associated microbiomes. Results show that TD may be polymicrobial, with multiple novel cellular and viral strains as potential players in the diarrheal disease.

Epidemiologic and Genotypic Distribution of Noroviruses Among Children With Acute Diarrhea and Healthy Controls in a Low-income Rural Setting

Background

Noroviruses are the most common cause of epidemic and endemic acute gastroenteritis (AGE) worldwide. The burden of norovirus disease in low-income settings is poorly understood.

Methods

We tested stool samples from children less than 5 years of age with diarrhea who were admitted in a rural hospital in Bangladesh from 2010–2012 and from matched, healthy controls from the same catchment area.

Results

Norovirus was detected in 109 (18%) of 613 children with diarrhea and in 30 (15%) of 206 healthy controls. Most (n = 118; 85%) norovirus infections belonged to genogroup II (GII). Of these, GII.4 viruses were identified in 36 (33%) of the cases and in 6 (21%) of the controls. Other major genotypes included GII.3 (13%), GII.6 (11%), and GII.13 (11%) in the cases and GII.6 (17%) and GII.2 (14%) in the controls. The greatest risk of severe norovirus disease (Vesikari score ≥11) was associated with GII.4 infections. GII.4 viruses were the predominant genotype detected during the winter (55%) and rainy season (23%), while GII.3 (19%) and GII.13 (19%) viruses were the most prevalent genotypes during the summer. Vomiting was significantly associated with GII.4 infections, while longer durations of diarrhea were associated with GI.3 infections.

Conclusions

Future studies are needed to understand the high rates of virus shedding in children without AGE symptoms.

Challenging Investigation of a Norovirus Foodborne Disease Outbreak During a Military Deployment in Central African Republic

In January 2016, a large-scale outbreak of acute gastroenteritis was reported among French armed forces deployed in the Central African Republic. Challenging investigations, conducted from France, made it possible to identify a norovirus genogroup II in both stool and food samples, confirming a norovirus foodborne disease outbreak. Infected food handler management is discussed.

Seafood pathogens and information on antimicrobial resistance: A review

Seafood-borne diseases are a major public health hazard in the United States and worldwide. Per capita, seafood consumption has increased globally during recent decades. Seafood importation and domestic aquaculture farming has also increased. Moreover, several recent outbreaks of human gastroenteritis have been linked to the consumption of contaminated seafood. Investigation of seafood-borne illnesses caused by norovirus, and Vibrio, and other bacteria and viruses require a concrete knowledge about the pathogenicity and virulence properties of the etiologic agents. This review explores pathogens that have been associated with seafood and resulting outbreaks in the U.S. and other countries as well as the presence of antimicrobial resistance in the reviewed pathogens. The spectrum of such resistance is widening due to the overuse, misuse, and sub-therapeutic application of antimicrobials in humans and animals.

Norovirus: new developments and implications for travelers' diarrhea

Noroviruses are the leading cause of acute gastroenteritis in the United States and are responsible for at least 50 % of acute gastroenteritis outbreaks occurring worldwide each year. In addition, noroviruses have caused outbreaks on cruise ships, in nursing homes and hospitals, and in deployed military personnel, but its role in the etiology of travelers’ diarrhea is not well defined. The aim of this review is to describe the role of noroviruses in travelers’ diarrhea in terms of epidemiology, current diagnostics, treatment and vaccine development efforts. Studies have shown prevalence rates of noroviruses in travelers’ diarrhea cases ranging from 10–65 %. It is likely that norovirus prevalence rates are highly underestimated in travelers’ diarrhea due to rapid onset, short duration of the illness, limited availability of laboratory facilities, and the fact that most clinical laboratories lack the diagnostic capability to detect noroviruses in stool. Further, additional studies are needed to accurately determine the true prevalence rates of norovirus as an etiologic agent of diarrhea among travelers to different regions around the world. With the rapid progress in the development of a norovirus vaccine, travelers could serve as an ideal population for future norovirus clinical trials.

Progress toward norovirus vaccines: considerations for further development and implementation in potential target populations

Human norovirus infection causes significant medical and financial costs in the USA and abroad. Some populations, including young children, the elderly, and the immunocompromised, are at heightened risk of infection with this virus and subsequent complications, while others, such as healthcare workers and food handlers are at increased risk of transmitting it, and some are at risk of both. Human noroviruses are heterogeneous with new strains emerging periodically. In addition to viral diversity, incompletely understood characteristics, such as virus-host cell binding and duration of immunity after infection add to the challenges of creating a norovirus vaccine. Although much progress has been made in recent years, many questions remain to be answered. In this review, we discuss the important areas and relevant literature in considering human norovirus vaccine development and potential targets for implementation.

Noroviruses as a Cause of Diarrhea in Immunocompromised Pediatric Hematopoietic Stem Cell and Solid Organ Transplant Recipients

Case reports describe significant norovirus gastroenteritis morbidity in immunocompromised patients. We evaluated norovirus pathogenesis in prospectively enrolled solid organ (SOT) and hematopoietic stem cell transplant (HSCT) patients with diarrhea who presented to Texas Children's Hospital and submitted stool for enteric testing. Noroviruses were detected by real-time reverse transcription polymerase chain reaction. Clinical outcomes of norovirus diarrhea and non-norovirus diarrhea patients, matched by transplanted organ type, were compared. Norovirus infection was identified in 25 (22%) of 116 patients, more frequently than other enteropathogens. Fifty percent of norovirus patients experienced diarrhea lasting ≥14 days, with median duration of 12.5 days (range 1-324 days); 29% developed diarrhea recurrence. Fifty-five percent of norovirus patients were hospitalized for diarrhea, with 27% requiring intensive care unit (ICU) admission. One HSCT recipient developed pneumatosis intestinalis. Three HSCT patients expired ≤6 months of norovirus diarrhea onset. Compared to non-norovirus diarrhea patients, norovirus patients experienced significantly more frequent ICU admission (27% vs. 0%, p = 0.02), greater serum creatinine rise (median 0.3 vs. 0.2 mg/dL, p = 0.01), and more weight loss (median 1.6 vs. 0.6 kg, p < 0.01). Noroviruses are an important cause of diarrhea in pediatric transplant patients and are associated with significant clinical complications.

Characterization of the human gut microbiome during travelers' diarrhea

Alterations in the gut microbiota are correlated with ailments such as obesity, inflammatory bowel disease, and diarrhea. Up to 60% of individuals traveling from industrialized to developing countries acquire a form of secretory diarrhea known as travelers' diarrhea (TD), and enterotoxigenic Escherichia coli (ETEC) and norovirus (NoV) are the leading causative pathogens. Presumably, TD alters the gut microbiome, however the effect of TD on gut communities has not been studied. We report the first analysis of bacterial gut populations associated with TD. We examined and compared the gut microbiomes of individuals who developed TD associated with ETEC, NoV, or mixed pathogens, and TD with no pathogen identified, to healthy travelers. We observed a signature dysbiotic gut microbiome profile of high Firmicutes:Bacteroidetes ratios in the travelers who developed diarrhea, regardless of etiologic agent or presence of a pathogen. There was no significant difference in α-diversity among travelers. The bacterial composition of the microbiota of the healthy travelers was similar to the diarrheal groups, however the β-diversity of the healthy travelers was significantly different than any pathogen-associated TD group. Further comparison of the healthy traveler microbiota to those from healthy subjects who were part of the Human Microbiome Project also revealed a significantly higher Firmicutes:Bacteriodetes ratio in the healthy travelers and significantly different β-diversity. Thus, the composition of the gut microbiome in healthy, diarrhea-free travelers has characteristics of a dysbiotic gut, suggesting that these alterations could be associated with factors such as travel.

Gastrointestinal symptoms in travellers

Diarrhoea is probably the single most common medical complaint in returning travellers. The most common pathogens are entero-toxigenic Escherichia coli, Shigella, Salmonella and Campylobacter. Viruses, toxigenic Arcobacter and Bacteroides fragilis, as well as parasites such as Cryptosporidium sp, are increasingly recognised but are not tested for in most diagnostic laboratories. Blood in stools is a sign of invasive disease and should trigger exclusion of invasive amoebic disease. The use of empiric antibiotics may shorten illness but is complicated by the diversity of bacterial causes and emerging resistance.

Mapping broadly reactive norovirus genogroup I and II monoclonal antibodies

Noroviruses are responsible for most acute nonbacterial epidemic outbreaks of gastroenteritis worldwide. To develop cross-reactive monoclonal antibodies (MAbs) for rapid identification of genogroup I and II (GI and GII) noroviruses (NoVs) in field specimens, mice were immunized with baculovirus-expressed recombinant virus-like particles (VLPs) corresponding to NoVs. Nine MAbs against the capsid protein were identified that detected both GI and GII NoV VLPs. These MAbs were tested in competition enzyme-linked immunosorbent assays (ELISAs) to identify common epitope reactivities to GI and GII VLPs. Patterns of competitive reactivity placed these MAbs into two epitope groups (groups 1 and 2). Epitopes for MAbs NV23 and NS22 (group 1) and MAb F120 (group 2) were mapped to a continuous region in the C-terminal P1 subdomain of the capsid protein. This domain is within regions previously defined to contain cross-reactive epitopes in GI and GII viruses, suggesting that common epitopes are clustered within the P1 domain of the capsid protein. Further characterization in an accompanying paper (B. Kou et al., Clin Vaccine Immunol 22:160-167, 2015, http://dx.doi.org/10.1128/CVI.00519-14) revealed that MAb NV23 (epitope group 1) is able to detect GI and GII viruses in stool. Inclusion of the GI and GII cross-reactive MAb NV23 in antigen detection assays may facilitate the identification of GI and GII human noroviruses in stool samples as causative agents of outbreaks and sporadic cases of gastroenteritis worldwide.

European Society for Pediatric Gastroenterology, Hepatology, and Nutrition/European Society for Pediatric Infectious Diseases evidence-based guidelines for the management of acute gastroenteritis in children in Europe: update 2014

OBJECTIVES

These guidelines update and extend evidence-based indications for the management of children with acute gastroenteritis in Europe.

METHODS

The guideline development group formulated questions, identified data, and formulated recommendations. The latter were graded with the Muir Gray system and, in parallel, with the Grading of Recommendations, Assessment, Development and Evaluations system.

RESULTS

Gastroenteritis severity is linked to etiology, and rotavirus is the most severe infectious agent and is frequently associated with dehydration. Dehydration reflects severity and should be monitored by established score systems. Investigations are generally not needed. Oral rehydration with hypoosmolar solution is the major treatment and should start as soon as possible. Breast-feeding should not be interrupted. Regular feeding should continue with no dietary changes including milk. Data suggest that in the hospital setting, in non-breast-fed infants and young children, lactose-free feeds can be considered in the management of gastroenteritis. Active therapy may reduce the duration and severity of diarrhea. Effective interventions include administration of specific probiotics such as Lactobacillus GG or Saccharomyces boulardii, diosmectite or racecadotril. Anti-infectious drugs should be given in exceptional cases. Ondansetron is effective against vomiting, but its routine use requires safety clearance given the warning about severe cardiac effects. Hospitalization should generally be reserved for children requiring enteral/parenteral rehydration; most cases may be managed in an outpatients setting. Enteral rehydration is superior to intravenous rehydration. Ultrarapid schemes of intravenous rehydration are not superior to standard schemes and may be associated with higher readmission rates.

CONCLUSIONS

Acute gastroenteritis is best managed using a few simple, well-defined medical interventions.

Seroepidemiology of norovirus-associated travelers' diarrhea

BACKGROUND

Noroviruses (NoVs) are the most common cause of epidemic gastroenteritis, responsible for at least 50% of all gastroenteritis outbreaks worldwide and were recently identified as a leading cause of travelers' diarrhea (TD) in US and European travelers to Mexico, Guatemala, and India.

METHODS

Serum and diarrheic stool samples were collected from 75 US student travelers to Cuernavaca, Mexico, who developed TD. NoV RNA was detected in acute diarrheic stool samples using reverse transcription-polymerase chain reaction (RT-PCR). Serology assays were performed using GI.1 Norwalk virus (NV) and GII.4 Houston virus (HOV) virus-like particles (VLPs) to measure serum levels of immunoglobulin A (IgA) and IgG by dissociation-enhanced lanthanide fluorescent immunoassay (DELFIA); serum IgM was measured by capture enzyme-linked immunosorbent assay (ELISA), and the 50% antibody-blocking titer (BT50 ) was determined by a carbohydrate-blocking assay.

RESULTS

NoV infection was identified in 12 (16%; 9 GI-NoV and 3 GII-NoV) of 75 travelers by either RT-PCR or fourfold or more rise in antibody titer. Significantly more individuals had detectable preexisting IgA antibodies against HOV (62/75, 83%) than against NV (49/75, 65%) (p = 0.025) VLPs. A significant difference was observed between NV- and HOV-specific preexisting IgA antibody levels (p = 0.0037), IgG (p = 0.003), and BT50 (p = <0.0001). None of the NoV-infected TD travelers had BT50  > 200, a level that has been described previously as a possible correlate of protection.

CONCLUSIONS

We found that GI-NoVs are commonly associated with TD cases identified in US adults traveling to Mexico, and seroprevalence rates and geometric mean antibody levels to a GI-NoV were lower than to a GII-NoV strain.

GIV Noroviruses in Wastewaters and in Stool Specimens from Hospitalized Patients

Noroviruses (NoVs) are important human pathogens associated with foodborne and waterborne gastroenteritis. These viruses are genetically highly heterogeneous, with more than forty genotypes within three genogroups (GI, GII, and GIV) identified in humans. However, the vast majority of human infections are associated with variants of a unique genotype, GII.4. Aside from these NoV strains of epidemiological relevance, NoV strains of genogroup GIV (Alphatron-like) are reported in a sporadic fashion and their overall prevalence in the community is unknown and this likely reflects the lack of specific diagnostic tools. We analyzed raw sewages collected from 32 wastewater treatment plants distributed throughout Italy (307 samples) and stool specimens collected from hospitalized patients with clinical signs of diarrhea of unknown etiology (285 samples). By using specific qualitative and quantitative RT-PCR assays, 21.8 % of the sewage samples and 3.2 % of the stool specimens tested positive for GIV NoVs. The number of genome copies in fecal samples ranged from 5.08 × 104 to 1.73× 106/g of feces. Sequence analysis showed limited genetic variability in human GIV viruses. The presence of GIV NoV both in sewage and in clinical samples confirms that not only GI and GII NoVs but also GIV strains are circulating in humans. Monitoring of GIV NoV is recommended in order to understand the dynamics of circulation in human populations, environmental contamination, and potential health risks.

Efficacy of rifaximin in prevention of travelers' diarrhea: a meta-analysis of randomized, double-blind, placebo-controlled trials

BACKGROUND

Rifaximin has been used successfully for the prevention of travelers' diarrhea (TD), the most general cause of disability among international travelers to developing tropical and semitropical regions.

METHODS

We sought to better evaluate the efficacy of rifaximin in the prevention of TD. Randomized controlled trials (RCTs) of rifaximin for the prevention of TD published in Pubmed, the Cochrane Central Register of Controlled Trials, Embase, and the Science Citation Index were searched. [Correction added on 3 October 2012, after first online publication: the phrase "protection of TD" was replaced with "prevention of TD".] The primary efficacy outcome was occurrence of TD over a 2-week treatment period. Secondary outcomes were requirement for antibiotic treatment, occurrence of mild diarrhea (MD), occurrence of TD in the third week after drug withdrawal, incidence of TD associated with isolation of diarrheagenic Escherichia coli (ie, ETEC, EAEC), and adverse events.

RESULTS

Four RCTs with 502 participants were included in the systematic review. Rifaximin treatment showed a significant protection against TD (risk ratios, RR: 0.41, 95% CI: 0.30-0.56, p < 0.00001) and needed antibiotic-treated TD (relative risk [RR]: 0.30, 95% confidence interval [CI]: 0.18-0.49, p < 0.00001). There was no significant difference between rifaximin and placebo in the occurrence of MD (RR: 1.11, 95% CI: 0.78-1.59, p = 0.55) and the occurrence of TD in the third week after drug withdrawal (RR: 0.73, 95% CI: 0.30-1.73, p = 0.47). Enterotoxigenic E. coli was the major cause of TD, and all trials reported no differences in adverse events between rifaximin and placebo.

CONCLUSIONS

Rifaximin can prevent TD caused by non-invasive enteric pathogens. Further research is needed for the treatment of invasive enteric pathogens. [Correction added on 3 October 2012, after first online publication: the phrase "Rifaximin can protect TD" was replaced with "Rifaximin can prevent TD".].

Secretory pathway antagonism by calicivirus homologues of Norwalk virus nonstructural protein p22 is restricted to noroviruses

Background

Our previous report that the Norwalk virus nonstructural protein p22 is an antagonist of the cellular secretory pathway suggests a new aspect of norovirus/host interaction. To explore conservation of function of this highly divergent calicivirus protein, we examined the effects of p22 homologues from four human and two murine noroviruses, and feline calicivirus on the secretory pathway.

Findings

All human noroviruses examined induced Golgi disruption and inhibited protein secretion, with the genogroup II.4 Houston virus being the most potent antagonist. Genogroup II.6 viruses have a conserved mutation in the mimic of an Endoplasmic Reticulum export signal (MERES) motif that is highly conserved in human norovirus homologues of p22 and is critical for secretory pathway antagonism, and these viruses had reduced levels of Golgi disruption and inhibition of protein secretion. p22 homologues from both persistent and nonpersistent strains of murine norovirus induced Golgi disruption, but only mildly inhibited cellular protein secretion. Feline calicivirus p30 did not induce Golgi disruption or inhibit cellular protein secretion.

Conclusions

These differences confirm a norovirus-specific effect on host cell secretory pathway antagonism by homologues of p22, which may affect viral replication and/or cellular pathogenesis.

Norovirus diagnostics: options, applications and interpretations

Noroviruses are a frequent cause of both acute gastroenteritis and outbreaks of gastroenteritis. Infection is usually self-limiting although it has been associated with mortality in children in the developing world and in vulnerable groups such as immunodeficient or immunosuppressed and elderly patients elsewhere. Diagnostic tests may be useful in preventing or limiting the spread and duration of outbreaks, and are needed to define norovirus-associated morbidity and mortality. However, the interpretation of test results should take account of the limitations of the different tests currently available. Therefore, the clinical, immunological and molecular tests available for norovirus detection have been reviewed. Early recognition of cases (clinical diagnoses) together with confirmation by sensitive and specific laboratory tests may contribute to reducing the spread of norovirus within hospitals. Syndromic testing that includes multiple or multiplex assays for the detection of viral, bacterial and parasitic pathogens with the inclusion of control groups are likely to better define norovirus-associated morbidity and mortality in low- and middle-income countries.

Advances in the treatment of travelers' diarrhea

Diarrhea is the most common complaint reported by travelers from industrialized countries visiting developing nations. High-risk areas for travelers' diarrhea (TD) include South Asia, Sub-Saharan Africa, and Latin America, while moderate-risk areas include Southeast Asia, Middle East, Oceania and the Caribbean. Bacterial pathogens are the major cause of TD. Recent advances in the therapy for diarrhea include a better understanding of the potential benefit of symptomatic and antimicrobial therapy. The mainstay of treatment includes antibacterial therapy with one of three drugs, a fluoroquinolone, rifaximin, or azithromycin. Probiotics have been used in preliminary studies for both treatment and prevention of TD, but more studies are needed with these biologic agents. The aim of this review is to identify the recent advances in the therapy of TD and to provide recommendations for treatment during international travel.

A randomized, double-blind, pilot study of rifaximin 550 mg versus placebo in the prevention of travelers' diarrhea in Mexico during the dry season

BACKGROUND

Rifaximin has been shown to be effective in treating and preventing travelers' diarrhea (TD) during the summer season.

METHODS

The goal of this double-blinded multicenter trial was to assess the efficacy and safety of rifaximin 550 mg administered once daily for 14 days compared with placebo in the prevention of TD during the dry season in Mexico.

RESULTS

There were 101 participants randomized. Overall, 25 participants developed TD during the 3 weeks of the study: 22% from the rifaximin group and 29% from the placebo group (p = 0.4). Mild diarrhea (defined as only one or two unformed stools during a 24-h period plus at least one abdominal symptoms) developed in only 3 (6%) participants taking rifaximin compared with 10 (21%) taking placebo during the first week of study (p = 0.03). No clinically significant or serious adverse events were reported.

CONCLUSIONS

Antibiotic prophylaxis of TD in Mexico during the dry season needs to be further studied and its benefits weighed against the benefits of self-treatment.

Impact of norovirus/sapovirus-related diarrhea in renal transplant recipients hospitalized for diarrhea

BACKGROUND

Diarrhea of unspecified cause frequently occurs after renal transplantation and is usually ascribed to mycophenolic acid toxicity. Norovirus (NoV) and sapovirus (SaV) have been sporadically reported to cause chronic diarrhea in immunocompromised patients.

METHODS

We undertook a retrospective study (2008-2009) to examine the clinical and epidemiologic significance of NoV and SaV infections in adult renal transplant recipients hospitalized for acute or chronic diarrhea.

RESULTS

Ninety-six renal transplant recipients were hospitalized for diarrhea at our institution during a 16-month period, 87 of whom were included in the study, including 46 patients with chronic diarrhea. Among 41 patients with unexplained diarrhea, 20 patients were screened for NoV/SaV, 16 of whom were positive. Fifteen of them (94%) had chronic diarrhea. When compared with bacterial and parasitic infections, NoV/SaV infections were associated with a greater weight loss at the time of admission, a 8.7-fold longer duration of symptoms and a more frequent need for mycophenolic acid dosage reduction. Eighty-one percent of patients hospitalized for NoV/SaV-associated diarrhea experienced acute renal failure. Five and one patients subsequently had biopsy-diagnosed active graft rejection and oxalate nephropathy, respectively. Ten of the 14 patients who underwent a longitudinal study of NoV/SaV stool's clearance exhibited a prolonged viral shedding period with a median time of 289 days (107-581 days).

CONCLUSIONS

Our study indicates that NoV/SaV infection causes posttransplant chronic diarrhea potentially complicated by severe kidney graft impairment.

New Developments in Traveler's Diarrhea

Traveler's diarrhea (TD) is a crucial area for research, as it affects millions of tourists each year and creates a large economic burden. More than 60% of TD cases are caused by a variety of bacterial enteropathogens: diarrhea-producing Escherichia coli, Shigella, Campylobacter, Salmonella, Aeromonas, Plesiomonas, and noncholera Vibrios. Noroviruses are also an important cause of morbidity among travelers. Recent studies have identified host genetic risk factors associated with susceptibility to pathogen-specific TD. Prevention strategies should be emphasized, as all individuals with TD experience approximately 24 hours of disability and 5-10% experience chronic functional bowel disease. Poorly absorbed rifaximin provides protection for trips lasting 2 weeks or less. TD vaccines are also currently in development. All individuals planning trips to developing regions should be armed with 1 of the 3 agents that have shown efficacy for self-treatment of TD: ciprofloxacin (or levofloxacin), rifaximin, or azithromycin, depending upon the location of the trip. Although global epidemiologic changes in etiologic agents as well as antibiotic resistance patterns have been better understood recently, changes should be expected during the next decade due to new prevention and treatment approaches.

Norovirus as a foodborne disease hazard

Norovirus (NoV) is the most common cause of infectious gastroenteritis in the world. Gastroenteritis caused by bacterial and parasitic pathogens is commonly linked to food sources, but the link between NoV and contaminated foods has been more difficult to establish. Even when epidemiological information indicates that an outbreak originated with food, the presence of NoV in the suspect product may not be confirmed. If food is found to contain a common strain of NoV that circulates widely in the community, it is not possible to use strain typing to link the contamination to patient cases. Although food is certainly implicated in NoV spread, there are additional person-to-person and fomite transmission routes that have been shown to be important. NoV has an extremely low infectious dose, is stable in the environment, and resists disinfection. Cell culture methods are not available, so viability cannot be determined. Finally, many NoV outbreaks originate with when an infected food handler contaminates ready-to-eat food, which can be interpreted as foodborne or person-to-person transmission. This review will discuss both the physical characteristics of NoVs and the available epidemiological information with particular reference to the role of foods in NoV transmission.

Noroviruses: The leading cause of gastroenteritis worldwide

Noroviruses are the leading cause of foodborne disease outbreaks worldwide, and may soon eclipse rotaviruses as the most common cause of severe pediatric gastroenteritis, as the use of rotavirus vaccines becomes more widespread. Genetic mutations and recombinations contribute to the broad heterogeneity of noroviruses and the emergence of new epidemic strains. Although typically a self-limited disease, norovirus gastroenteritis can cause significant morbidity and mortality among children, the elderly, and the immunocompromised. The lack of a cell culture or small animal model has hindered norovirus research and the development of novel therapeutic and preventative interventions. However, vaccines based on norovirus capsid protein virus-like particles are promising and may one day become widely available through transgenic expression in plants.