Risk of travel-associated typhoid and paratyphoid fevers in various regions

Spatiotemporal distribution and influencing factors of enteric fever in China: a cluster analysis based on data from 2001 to 2020

Background

Enteric fever primarily affects the southwestern and central regions of China. Although the overall incidence rate has declined, certain areas have seen an increase in cases, necessitating further investigation into their geographic distribution, clustering areas, and potential influencing factors.

Methods

City-level data from 2001 to 2020 were analyzed. Spatial clustering was identified, and wavelet transform analysis explored periodic and seasonal characteristics. Determinants were identified using generalized estimating equation and distributed lag non-linear model.

Results

Incidence declined from 2001 to 2008 but leveled off since 2009, shifting eastward. Two clustering areas were identified: Guangxi-Guizhou-Yunnan and Zhejiang. In the Zhejiang, incidence was negatively correlated with GDP per capita and popularization rate of safe drinking water in rural areas. Temperature and relative humidity had delayed effects on incidence in Zhejiang, showing linear or parabolic patterns. In the Guangxi-Guizhou-Yunnan, incidence was positively correlated with the proportion of water bodies. Temperature and relative humidity had delayed effects on incidence in Guangxi-Guizhou-Yunnan, and these effects exhibited fluctuating patterns.

Conclusions

Over the past 20 years, enteric fever incidence in China has shown a rapid early decline but has stabilized more recently. The factors influencing enteric fever prevalence vary between clustering areas, indicating the need for region-specific measures.

Global burden, trends and inequalities for typhoid and paratyphoid fever among children younger than 15 years over the past 30 years

BACKGROUND

Typhoid and paratyphoid fever, collectively known as enteric fever, are systemic infections caused by Salmonella enterica and are highly prevalent in children. We aimed to describe the global burden, trends and inequalities of enteric fever among children under 15 years from 1990 to 2019 based on data from the Global Burden of Diseases, Injuries, and Risk Factors Study 2019 (GBD 2019).

METHODS

In this secondary analysis of GBD 2019, we extracted data for incident cases, deaths and disability-adjusted life-years (DALYs) as measures of enteric fever burden. We estimated the average annual percentage changes (AAPCs) in enteric fever incidence, mortality and DALYs rate to quantify trends over time. Cross-country inequalities in enteric fever incidence were measured using the slope index of inequality and concentration index.

RESULTS

In 2019, the global cases of typhoid and paratyphoid were 4 833 282 and 1 793 172, respectively, both lower than those in 1990. On secondary analysis, paratyphoid incidence decreased at a faster rate than typhoid from 1990 to 2009, whereas the incidence of paratyphoid (AAPC = -3.78, 95% CI: -4.07, -3.49) declined slower than that of typhoid (AAPC = -4.32, 95% CI: -4.50, -4.13) from 2010 to 2019 (P < 0.05) at the global level. The incidence burden of enteric fever increased in Australasia (AAPC = 1.28, 95% CI: 0.77, 1.78) and Western Europe (AAPC = 0.77, 95% CI: 0.44, 1.11). Death and DALYs burden in low socio-demographic index (SDI) region showed a stable trend. A significant reduction in SDI-related inequality occurred, with the concentration index falling from -0.31 in 1990 to -0.22 in 2019.

CONCLUSIONS

The global disease burden of enteric fever and the magnitude of inequalities across countries have declined since 1990, but low SDI countries remain a region of concern. Travellers from Oceania and Western Europe to endemic regions should be particularly aware of the risk of enteric fever.

Effects of sanitation and hygiene perceptions on international travelers' health, travel plans and trip experiences in India

Background

International travelers often experience travelers' diarrhea. However, there is paucity of data on whether self-reported gastrointestinal symptoms influence travelers' perceptions of adequacy of sanitation and hygiene services encountered during travel, and to what degree their travel plans, and overall trip experience are impacted.

Methods

A cross-sectional face-to-face survey was conducted amongst international travelers in India. Data collected included socio-demographics, travel characteristics, self-reported occurrence and frequency/severity of gastrointestinal symptoms, perceptions of sanitation and hygiene encountered, and adverse effects of symptoms on travel plans and trip experiences. Chi-square tests and logistic regression were performed to describe differences and associations between categorical variables.

Results

Of the 300 international travelers surveyed, 46.3% experienced diarrhea. At least two thirds of travelers perceived the quality of sanitation (67.0%) and hygiene (70.0%) encountered to be inadequate. Perceptions of inadequate sanitation (adjusted OR = 3.0; 95% CI 1.7-5.5) and poor hygiene (adjusted OR = 7.7; 95% CI 4.1-15.5) were higher among travelers who experienced diarrhea. Additionally, both higher likelihood of travel plans being affected (adjusted OR = 10.7; 95% CI 5.1-23.6) and adverse impacts on overall trip experience (adjusted OR = 2.8; 95% CI 1.4-5.8) were reported among those who experienced diarrhea.

Conclusions

More than two thirds of travelers surveyed in India experienced inadequate sanitation and hygiene services, with perceptions influenced by occurrence and frequency of diarrhea. Self-reported diarrhea was also associated with adverse effects on travel plans and overall trip experience. While these results may seem intuitive, they have important implications and suggest that improving sanitation and hygiene standards in India could potentially enhance tourism.

Vaccines and Senior Travellers

Background: International tourist travel has been increasingly steadily in recent years, and looks set to reach unprecedented levels in the coming decades. Among these travellers, an increasing proportion is aged over 60 years, and is healthy and wealthy enough to be able to travel. However, senior travellers have specific risks linked to their age, health and travel patterns, as compared to their younger counterparts. Methods: We review here the risk of major vaccine-preventable travel-associated infectious diseases, and forms and efficacy of vaccination for these diseases. Results: Routine vaccinations are recommended for older persons, regardless of whether they travel or not (e.g., influenza, pneumococcal vaccines). Older individuals should be advised about the vaccines that are recommended for their age group in the framework of the national vaccination schedule. Travel-specific vaccines must be discussed in detail on a case-by-case basis, and the risk associated with the vaccine should be carefully weighed against the risk of contracting the disease during travel. Travel-specific vaccines reviewed here include yellow fever, hepatitis, meningococcal meningitis, typhoid fever, cholera, poliomyelitis, rabies, Japanese encephalitis, tick-borne encephalitis and dengue. Conclusion: The number of older people who have the good health and financial resources to travel is rising dramatically. Older travellers should be advised appropriately about routine and travel-specific vaccines, taking into account the destination, duration and purpose of the trip, the activities planned, the type of accommodation, as well as patient-specific characteristics, such as health status and current medications.

Typhoid and paratyphoid fever: a clinical seminar

Rationale for review: Enteric fever (EF) caused by Salmonella enterica subspecies enterica serovar Typhi (Salmonella Typhi) and S. Paratyphi (Salmonella Paratyphi) remains an important cause of infectious morbidity and mortality in many low-income countries and, therefore, still poses a major infectious risk for travellers to endemic countries. Main findings: Although the global burden of EF has decreased over the past two decades, prevalence of EF remains high in Asia and Africa, with the highest prevalence reported from the Indian subcontinent. These statistics are mirrored by data on travel-related EF. Widespread and increasing antimicrobial resistance has narrowed treatment options for travel-related EF. Ceftriaxone- and azithromycin-based therapies are commonly used, even with the emergence of extremely drug-resistant typhoid in Pakistan. Preventive measures among locals and travellers include provision of safe food and water and vaccination. Food and water precautions offer limited protection, and the efficacy of Salmonella Typhi vaccines is only moderate signifying the need for travellers to be extra cautious. Recommendations: Improvement in the diagnosis of typhoid with high degree of clinical suspicion, better diagnostic assays, early and accurate detection of resistance, therapy with appropriate drugs, improvements in hygiene and sanitation with provision of safe drinking water in endemic areas and vaccination among travellers as well as in the endemic population are keys to controlling typhoid. While typhoid vaccines are recommended for travellers to high-risk areas, moderate efficacy and inability to protect against Salmonella Paratyphi are limitations to bear in mind. Improved Salmonella Typhi vaccines and vaccines against Salmonella Paratyphi A are required.

Typhoid fever infection - Antibiotic resistance and vaccination strategies: A narrative review

Typhoid fever is a bacterial infection caused by the Gram-negative bacterium Salmonella enterica subspecies enterica serovar Typhi (S. Typhi), prevalent in many low- and middle-income countries. In high-income territories, typhoid fever is predominantly travel-related, consequent to travel in typhoid-endemic regions; however, data show that the level of typhoid vaccination in travellers is low. Successful management of typhoid fever using antibiotics is becoming increasingly difficult due to drug resistance; emerging resistance has spread geographically due to factors such as increasing travel connectivity, affecting those in endemic regions and travellers alike. This review provides an overview of: the epidemiology and diagnosis of typhoid fever; the emergence of drug-resistant typhoid strains in the endemic setting; drug resistance observed in travellers; vaccines currently available to prevent typhoid fever; vaccine recommendations for people living in typhoid-endemic regions; strategies for the introduction of typhoid vaccines and stakeholders in vaccination programmes; and travel recommendations for a selection of destinations with a medium or high incidence of typhoid fever.

The use and reporting of airline passenger data for infectious disease modelling: a systematic review

BackgroundA variety of airline passenger data sources are used for modelling the international spread of infectious diseases. Questions exist regarding the suitability and validity of these sources.AimWe conducted a systematic review to identify the sources of airline passenger data used for these purposes and to assess validation of the data and reproducibility of the methodology.MethodsArticles matching our search criteria and describing a model of the international spread of human infectious disease, parameterised with airline passenger data, were identified. Information regarding type and source of airline passenger data used was collated and the studies' reproducibility assessed.ResultsWe identified 136 articles. The majority (n = 96) sourced data primarily used by the airline industry. Governmental data sources were used in 30 studies and data published by individual airports in four studies. Validation of passenger data was conducted in only seven studies. No study was found to be fully reproducible, although eight were partially reproducible.LimitationsBy limiting the articles to international spread, articles focussed on within-country transmission even if they used relevant data sources were excluded. Authors were not contacted to clarify their methods. Searches were limited to articles in PubMed, Web of Science and Scopus.ConclusionWe recommend greater efforts to assess validity and biases of airline passenger data used for modelling studies, particularly when model outputs are to inform national and international public health policies. We also recommend improving reporting standards and more detailed studies on biases in commercial and open-access data to assess their reproducibility.

Typhoid Vaccination among Japanese Travelers to South Asia and the Factors Associated with Compliance

Objective In 2010, candid advice concerning the low rate of typhoid vaccination among Japanese travelers was received from Nepal. Recently, progressive Japanese travel clinics have encouraged Japanese travelers to be vaccinated against typhoid fever in conjunction with officially approved vaccines, such as hepatitis A vaccine. We herein report the status of typhoid vaccinations for Japanese travelers to the most endemic area (South Asia) and describe the factors associated with compliance. Methods In the travel clinic at Kurume University Hospital, we used the following criteria to retrospectively extract the records of new pre-travel Japanese clients between January 2011 and March 2015: hepatitis A vaccine administered, traveling to South Asian countries, and ≥2 years of age. We first summarized the participants and then divided them into typhoid-vaccinated and typhoid non-vaccinated groups for a comparative analysis. Results This study included 160 clients. A majority (70.0%) of these clients traveled for business. The duration of trips was long (≥1 month) (75.0%), and India was a popular destination (90.6%). A comparative study between the vaccinated group (n=122) and the non-vaccinated group (n=38) revealed that the two factors most positively associated with typhoid vaccination were business trips [adjusted odds ratio (aOR) 3.59, 95% confidence interval (CI) 1.42-9.06] and coverage by a company/organization payment plan (aOR 7.14, 95% CI 2.67-20.3). Conclusion The trend toward typhoid vaccination among Japanese travelers to South Asia with pre-travel consultation is correlated with business trips and coverage by a company/organization payment plan. If problems concerning the cost of vaccines were resolved, more travelers would request typhoid vaccination.

Self-reported infections during international travel and notifiable infections among returning international travellers, Sweden, 2009-2013

We studied food and water-borne diseases (FWDs), sexually transmitted diseases (STDs), vector-borne diseases (VBDs) and diseases vaccinated against in the Swedish childhood vaccination programme among Swedish international travellers, in order to identify countries associated with a high number of infections. We used the national database for notifiable infections to estimate the number of FWDs (campylobacteriosis, salmonellosis, giardiasis, shigellosis, EHEC, Entamoeba histolytica, yersinosis, hepatitis A, paratyphoid fever, typhoid fever, hepatitis E, listeriosis, cholera), STIs (chlamydia, gonorrhoea and acute hepatitis B), VBDs (dengue fever, malaria, West Nile fever, Japanese encephalitis and yellow fever) and diseases vaccinated against in the Swedish childhood vaccination programme (pertussis, measles, mumps, rubella, diphtheria) acquired abroad 2009–2013. We obtained number and duration of trips to each country from a database that monthly collects travel data from a randomly selected proportion of the Swedish population. We calculated number of infections per country 2009–2013 and incidence/million travel days for the five countries with the highest number of infections. Thailand had the highest number of FWDs (7,697, incidence 191/million travel days), STIs (1,388, incidence 34/million travel days) and VBDs (358, incidence 9/million travel days). France had the highest number of cases of diseases vaccinated against in the Swedish childhood vaccination programme (8, 0.4/million travel days). Swedish travellers contracted most infections in Thailand. Special focus should be placed on giving advice to travellers to this destination.

Burden of typhoid fever in low-income and middle-income countries: a systematic, literature-based update with risk-factor adjustment

BACKGROUND

No access to safe water is an important risk factor for typhoid fever, yet risk-level heterogeneity is unaccounted for in previous global burden estimates. Since WHO has recommended risk-based use of typhoid polysaccharide vaccine, we revisited the burden of typhoid fever in low-income and middle-income countries (LMICs) after adjusting for water-related risk.

METHODS

We estimated the typhoid disease burden from studies done in LMICs based on blood-culture-confirmed incidence rates applied to the 2010 population, after correcting for operational issues related to surveillance, limitations of diagnostic tests, and water-related risk. We derived incidence estimates, correction factors, and mortality estimates from systematic literature reviews. We did scenario analyses for risk factors, diagnostic sensitivity, and case fatality rates, accounting for the uncertainty in these estimates and we compared them with previous disease burden estimates.

FINDINGS

The estimated number of typhoid fever cases in LMICs in 2010 after adjusting for water-related risk was 11·9 million (95% CI 9·9-14·7) cases with 129 000 (75 000-208 000) deaths. By comparison, the estimated risk-unadjusted burden was 20·6 million (17·5-24·2) cases and 223 000 (131 000-344 000) deaths. Scenario analyses indicated that the risk-factor adjustment and updated diagnostic test correction factor derived from systematic literature reviews were the drivers of differences between the current estimate and past estimates.

INTERPRETATION

The risk-adjusted typhoid fever burden estimate was more conservative than previous estimates. However, by distinguishing the risk differences, it will allow assessment of the effect at the population level and will facilitate cost-effectiveness calculations for risk-based vaccination strategies for future typhoid conjugate vaccine.

Vaccine-preventable travel health risks: what is the evidence--what are the gaps?

BACKGROUND

Existing travel health guidelines are based on a variety of data with underpinning evidence ranging from high-quality randomized controlled trials to best estimates from expert opinion. For strategic guidance and to set overall priorities, data about average risk are useful. The World Health Organization (WHO) plans to base future editions of "International Travel and Health" on its new "Handbook for Guideline Development."

METHODS

Based on a systematic search in PubMed, the existing evidence and quality of data on vaccine-preventable disease (VPD) risks in travelers was examined and essentials of vaccine efficacy were briefly reviewed. The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework was used to evaluate the quality of the data.

RESULTS

Moderate-quality data to determine the risk of VPD exist on those that are frequently imported, whereas in most others the level of confidence with existing data is low or very low.

CONCLUSIONS

In order for the WHO to produce graded risk statements in the updated version of "International Travel and Health," major investment of time plus additional high-quality, generalizable risk data are needed.

Cross-reactive immune response induced by the Vi capsular polysaccharide typhoid vaccine against Salmonella Paratyphi strains

There are no vaccines in clinical use against paratyphoid fever, caused by Salmonella Paratyphi A and B or, rarely, C. Oral Salmonella Typhi Ty21a typhoid vaccine elicits a significant cross-reactive immune response against S. Paratyphi A and B, and some reports suggest cross-protective efficacy against the disease. These findings are ascribed to the O-12 antigen shared between the strains. The Vi capsular polysaccharide vaccine has been shown to elicit antibodies reactive with O-9,12. Twenty-five volunteers immunized with the parenteral Vi vaccine (Typherix(®) ) were explored for plasmablasts cross-reactive with paratyphoid strains; the responses were compared to those in 25 age- and gender-matched volunteers immunized with Ty21a (Vivotif(®) ). Before vaccination, 48/50 vaccinees had no plasmablasts reactive with the antigens. Seven days after vaccination, 15/25 and 22/25 Vi- and Ty21a-vaccinated volunteers had circulating plasmablasts producing antibodies cross-reactive with S. Paratyphi A, 18/25 and 23/25 with S. Paratyphi B and 16/25 and 9/25 with Paratyphi C, respectively. Compared to the Ty21a group, the Vi group showed significantly lower responses to S. Paratyphi A and B and higher to S. Paratyphi C. To conclude, the Vi vaccine elicited a cross-reactive plasmablast response to S. Paratyphi C (Vi antigen in common) and less marked responses to S. Paratyphi A and B than the Ty21a preparation. S. Paratyphi A and B both being Vi-negative, the result can be explained by trace amounts of bacterial cell wall O-12 antigen in the Vi preparation, despite purification. The clinical significance of this finding remains to be determined.

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

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

Antimicrobial resistance in Salmonella enterica serovar typhi and paratyphi in South Asia-current status, issues and prospects

The human race owes a debt of gratitude to antimicrobial agents, penicillin and its successors that have saved people from tremendous pain and suffering in the last several decades. Unfortunately, this consideration is no more true, as millions of people are prone to the challenging threat of emergence of antimicrobial resistance worldwide and the menace is more distressing in developing countries. Comparable with other bacterial species, Salmonella enterica serovar Typhi (S. typhi) and Paratyphi (S. paratyphi) have been evolving multidrug resistance (MDR) against a wide array of antibiotics, including chloramphenicol, ampicillin and co-trimoxazole, and globally affecting 21 million people with 220,000 deaths each year. S. typhi and S. paratyphi infections are also endemic in South Asia and a series of antibiotics used to treat these infections, have been losing efficacy against enteric fever. Currently, quinolones are regarded as a choice to treat MDR Salmonella in these regions. Travel-related cases of enteric fever, especially from South Asian countries are the harbinger of the magnitude of MDR Salmonella in that region. Conclusively, the MDR will continue to grow and the available antimicrobial agents would become obsolete. Therefore, a radical and aggressive approach in terms of rational use of antibiotics during treating infections is essentially needed.

Travel-associated illness trends and clusters, 2000-2010

Longitudinal data examining travel-associated illness patterns are lacking. To address this need and determine trends and clusters in travel-related illness, we examined data for 2000–2010, prospectively collected for 42,223 ill travelers by 18 GeoSentinel sites. The most common destinations from which ill travelers returned were sub-Saharan Africa (26%), Southeast Asia (17%), south-central Asia (15%), and South America (10%). The proportion who traveled for tourism decreased significantly, and the proportion who traveled to visit friends and relatives increased. Among travelers returning from malaria-endemic regions, the proportionate morbidity (PM) for malaria decreased; in contrast, the PM trends for enteric fever and dengue (excluding a 2002 peak) increased. Case clustering was detected for malaria (Africa 2000, 2007), dengue (Thailand 2002, India 2003), and enteric fever (Nepal 2009). This multisite longitudinal analysis highlights the utility of sentinel surveillance of travelers for contributing information on disease activity trends and an evidence base for travel medicine recommendations.

Risk for travel-associated legionnaires' disease, Europe, 2009

Legionnaires' disease is underreported in Europe; notification rates differ substantially among countries. Approximately 20% of reported cases are travel-associated. To assess the risk for travel-associated Legionnaires' disease (TALD) associated with travel patterns in European countries, we retrieved TALD surveillance data for 2009 from the European Surveillance System, and tourism denominator data from the Statistical Office of the European Union. Risk (number cases reported/number nights spent) was calculated by travel country. In 2009, the network reported 607 cases among European travelers, possibly associated with 825 accommodation sites in European Union countries. The overall risk associated with travel abroad was 0.3 cases/million nights. We observed an increasing trend in risk from northwestern to southeastern Europe; Greece had the highest risk (1.7). Our findings underscore the need for countries with high TALD risks to improve prevention and control of legionellosis; and for countries with high TALD risks, but low notification rates of Legionnaires' disease to improve diagnostics and reporting.

O:2-CRM(197) conjugates against Salmonella Paratyphi A

Enteric fevers remain a common and serious disease, affecting mainly children and adolescents in developing countries. Salmonella enterica serovar Typhi was believed to cause most enteric fever episodes, but several recent reports have shown an increasing incidence of S. Paratyphi A, encouraging the development of a bivalent vaccine to protect against both serovars, especially considering that at present there is no vaccine against S. Paratyphi A. The O-specific polysaccharide (O:2) of S. Paratyphi A is a protective antigen and clinical data have previously demonstrated the potential of using O:2 conjugate vaccines. Here we describe a new conjugation chemistry to link O:2 and the carrier protein CRM(197), using the terminus 3-deoxy-D-manno-octulosonic acid (KDO), thus leaving the O:2 chain unmodified. The new conjugates were tested in mice and compared with other O:2-antigen conjugates, synthesized adopting previously described methods that use CRM(197) as carrier protein. The newly developed conjugation chemistry yielded immunogenic conjugates with strong serum bactericidal activity against S. Paratyphi A.

From the CDC: new country-specific recommendations for pre-travel typhoid vaccination

Typhoid fever continues to be an important concern for travelers visiting many parts of the world. This communication provides updated guidance for pre-travel typhoid vaccination from the US Centers for Disease Control and Prevention (CDC) and describes the methodology for assigning country-specific recommendations.

International travel and the risk of hospitalization with non-typhoidal Salmonella bacteremia. A Danish population-based cohort study, 1999-2008

Background

Information is sparse regarding the association between international travel and hospitalization with non-typhoidal Salmonella bacteremia. The aim of this study was to determine the proportion, risk factors and outcomes of travel-related non-typhoidal Salmonella bacteremia.

Methods

We conducted a 10-year population-based cohort study of all patients hospitalized with non-typhoidal Salmonella bacteremia in three Danish counties (population 1.6 million). We used denominator data on Danish travellers to assess the risk per 100,000 travellers according to age and travel destination. We used patients contemporaneously diagnosed with travel-related Salmonella gastroenteritis as reference patients to estimate the relative risk of presenting with travel-related bacteremia as compared with gastroenteritis. To evaluate clinical outcomes, we compared patients with travel-related bacteremia and patients with domestically acquired bacteremia in terms of length of hospital stay, number of extraintestinal focal infections and mortality after 30 and 90 days.

Results

We identified 311 patients hospitalized with non-typhoidal Salmonella bacteremia of whom 76 (24.4%) had a history of international travel. The risk of travel-related bacteremia per traveller was highest in the age groups 15-24 years (0.8/100,000 travellers) and 65 years and above (1.2/100,000 travellers). The sex- and age-adjusted relative risk of presenting with bacteremia was associated with travel to Sub-Saharan Africa (odds ratio 18.4; 95% confidence interval [6.9-49.5]), the Middle East (10.6; [2.1-53.2]) and South East Asia (4.0; [2.2-7.5]). We found high-risk countries in the same three regions when estimating the risk per traveller according to travel destination. Patients hospitalized with travel-related bacteremia had better clinical outcomes than patients with domestically acquired bacteremia, they had a shorter length of hospital stay (8 vs. 11 days), less extraintestinal focal infections (5 vs. 31 patients) and a lower risk of death within both 30 days (relative risk 0.2; [0.1-0.7]) and 90 days (0.3; [0.1-0.7]). A healthy traveller effect was a plausible explanation for the observed differences in outcomes.

Conclusions

International travel is a notable risk factor for being hospitalized with non-typhoidal Salmonella bacteremia and the risk differs between age groups and travel destinations. Healthy travellers hospitalized with bacteremia are less likely to have poor outcomes than patients with domestically acquired bacteremia.

Epidemiology of enteric disease in C-EnterNet's pilot site - Waterloo region, Ontario, 1990 to 2004

OBJECTIVE

The objective of the present study was to describe the epidemiology of reportable enteric illness in Ontario's Waterloo region, including comparing calculated incidence rates with published rates, and adjusting for under-reporting to determine the number of community cases, where published data were available.

METHODS

Descriptive analyses were performed on reportable disease data for 13 enteric diseases collected in the Waterloo region from 1990 to 2004. Poisson and negative binomial regression analyses were used to investigate differences in incidence rates among age, sex, the 15 years of data and seasons. Disease-specific incidence rates were calculated and compared with the literature, where possible. Under-reporting ratios from the literature were applied to estimate the number of cases of campylobacteriosis, nontyphoidal salmonellosis and verotoxigenic Escherichia coli infection at the community level.

RESULTS

Over the study period, the average annual age- and sex-adjusted incidence rates per 100,000 population were highest for campylobacteriosis (49.69 cases), followed by giardiasis (31.87 cases) and nontyphoidal salmonellosis (25.97 cases). The incidence of most enteric illnesses peaked in the summer. The highest incidence occurred in young children, followed by adults in their 20s. Diarrhea (85.4%) was the most frequently reported symptom, food (57.4%) was the most commonly reported probable source, and home (41.7%) and travel (37.0%) were the two most frequently reported risk settings.

CONCLUSIONS

Enteric illness was a significant health burden in the Waterloo region from 1990 to 2004. Because reportable disease data are subject to under-reporting, it is likely that the true burden is greater than estimated in the present study.

The impact of international travel on the epidemiology of enteric infections, British Columbia, 2008

OBJECTIVE

Travel-related enteric infections likely represent a large proportion of all enteric infections in British Columbia (BC). The objective of this study was to assess the proportion of enteric infections in BC reported in 2008 associated with international travel in order to understand trends in infections so that targeted interventions can be implemented.

METHODS

Travel information for all reported cases of salmonellosis, verotoxigenic E. coli (VTEC) infection, shigellosis, Vibrio parahemolyticus infection, botulism, cholera, listeriosis, typhoid fever, paratyphoid fever, hepatitis A infection, cryptosporidiosis, cyclosporiasis and a representative proportion of campylobacteriosis was collected. Temporal, demographic and geographic analysis was conducted comparing locally-acquired infections to infections acquired during international travel. Travel destination was compared between cases of enteric infections and the BC population.

RESULTS

Of the 3,120 enteric infections reported in 2008, 60% were classified as locally-acquired and 40% were associated with international travel. The proportion of infections associated with international travel was highest among 30 to 39 year olds. Locally-acquired infections were highest in the summer months and international travel-related infections were highest in the winter. Asia and Mexico were the most common destinations in relation to enteric infections acquired internationally. The proportion of enteric infections was significantly higher than the proportion of the BC population travelling to these areas.

CONCLUSIONS

The proportion of enteric infections in BC associated with international travel is significant. Identification and assessment of locally-acquired infections separately from those associated with international travel will improve assessment of trends and rates for enteric infections in BC and lead to more targeted public health actions.

Enteric fever: a travel medicine oriented view

PURPOSE OF REVIEW

Enteric fever continues to be an important infection among populations in endemic countries and among travelers to these areas. This review aims to describe recent epidemiological trends and developments in diagnosis, treatment and prevention.

RECENT FINDINGS

Data indicate that the burden of enteric fever is declining in many middle-income countries, whereas the bulk of cases occur in the Indian subcontinent and in south-east Asia. In these regions, Salmonella Paratyphi A is increasingly seen and sometimes surpasses Salmonella Typhi as the main pathogen. Enteric fever caused by S. Paratyphi A is indistinguishable from that caused by S. Typhi. In addition, drug resistance, including nalidixic acid/quinolone resistance now occurs in the majority of clinical isolates of S. Typhi and S. Paratyphi A in Asia. Currently, third generation cephalosporins and azythromycin are the only reasonable therapeutic options for most cases of travel-related enteric fever.

SUMMARY

The ongoing emergence of S. Paratyphi A results in partial benefit from current typhoid vaccines in the prevention of enteric fever in travelers. Increasing antimicrobial resistance complicates therapy for travel-related enteric fever. New vaccines, offering protection against both agents of enteric fever, are urgently needed; however, none of the current vaccine candidates is likely to be available for several years.

Travel medicine research priorities: establishing an evidence base

BACKGROUND

Travel medicine is the medical subspecialty which promotes healthy and safe travel. Numerous studies have been published that provide evidence for the practice of travel medicine, but gaps exist.

METHODS

The Research Committee of the International Society of Travel Medicine (ISTM) established a Writing Group which reviewed the existing evidence base and identified an initial list of research priorities through an interactive process that included e-mails, phone calls, and smaller meetings. The list was presented to a broader group of travel medicine experts, then was presented and discussed at the Annual ISTM Meeting, and further revised by the Writing Group. Each research question was then subject to literature search to ensure that adequate research had not already been conducted.

RESULTS

Twenty-five research priorities were identified and categorized as intended to inform pre-travel encounters, safety during travel, and post-travel management.

CONCLUSION

We have described the research priorities that will help to expand the evidence base in travel medicine. This discussion of research priorities serves to highlight the commitment that the ISTM has in promoting quality travel-related research.

Imported enteric fever: case series from the hospital for tropical diseases, London, United Kingdom

Our current knowledge of the clinical characteristics of enteric fever is drawn mainly from population-based studies in disease-endemic countries, and there are limited data published on cases in returning travelers. We report the clinical characteristics of enteric fever in 92 travelers returning to London, United Kingdom. Salmonella typhi and S. paratyphi resulted in an almost indistinguishable clinical picture. Rose spots and relative bradycardia were found only in a few patients. A total of 91% of the patients had a normal leukocyte count, which was associated with a markedly increased level of alanine aminotransferase in 82%. A total of 57% of the S. typhi isolates had decreased susceptibility to ciprofloxacin and resistance to nalidixic acid; these isolates were from southern Asia. Thirty percent were multidrug resistant; all were from southern Asia and Nigeria. None of the paratyphoid isolates were multidrug resistant but rates of decreased susceptibility to fluoroquinolones were higher than in S. typhi (74%).

Descriptive epidemiology of travel-associated diarrhea based on surveillance data at Narita International Airport

BACKGROUND

Although travelers' diarrhea is one of the most common health problems among international travelers, current findings depend largely on hospital and clinic-based information. To better understand the disease epidemiology and to identify specific subpopulations with increased risks, denominator data covering a large traveler population are needed.

METHODS

We conducted a questionnaire survey of all travelers at the quarantine station, Narita International Airport, and retrospectively reviewed records from January 2001 to December 2005. The Immigration Bureau database was used as denominator data on travel patterns during the same period. To elucidate the risks of contracting diarrhea, we estimated incidence according to age, sex, month of travel, and travel destination.

RESULTS

A total of 7,937,654 people voluntarily submitted questionnaires; 9,836 had travelers' diarrhea. Travelers of both sexes aged 20 to 29 years reported the disease most frequently. Men aged 20 to 24 had the highest estimated incidence compared with any other age and sex group. The incidence was higher in March, August, and September than other months, mainly due to the influx of young adult travelers. Travel to south-central Asia, Southeast Asia, and North Africa was associated with higher risks than that to other areas.

CONCLUSIONS

Risks of contracting travelers' diarrhea are dependent on age, sex, season, and destination of travel. Incidence of diarrhea in all four seasons varies with age. Some destinations are associated with increased risks regardless of age. To prevent travelers from contracting diarrhea, adequate measures should focus on specific subpopulations.

Increasing rates and clinical consequences of nalidixic acid-resistant isolates causing enteric fever in returned travellers: an 18-year experience

The purpose of this study was to examine the rate and clinical consequences of nalidixic acid-resistant (NAR) isolates in travellers with enteric fever presenting to a hospital in a developed country. We retrospectively examined microbiologically confirmed cases of enteric fever in adult returned travellers over an 18-year period presenting to two tertiary referral hospitals in Melbourne, Australia. There were 59 cases of Salmonella typhi infection, 43 cases of S. paratyphi A infection and two cases of S. paratyphi B infection. Most patients reported recent travel to India (36%) or Indonesia (29%). NAR isolates were commonly encountered (41% of all isolates), particularly from India (75%), Pakistan (80%) and Bangladesh (60%). The number of NAR isolates increased progressively after 2003. Patients with NAR isolates had prolonged mean fever clearance time (5.6 vs. 3.3 days, P = 0.03) and prolonged hospital stay (7.9 vs. 5.7 days, P = 0.02) compared to non-resistant isolates. This represents the largest report of NAR enteric fever in returned travellers. NAR isolates predominate in cases of enteric fever from South Asia and result in prolonged fever clearance time and hospital stay. Empiric therapy with alternative antibiotics such as ceftriaxone or azithromycin should be considered in patients with suspected enteric fever from this region.

Imported typhoid fever in Switzerland, 1993 to 2004

BACKGROUND

In industrialized countries, typhoid fever occurs mainly in returned travelers. To determine the need for preventive strategies, eg, for vaccination, continuous monitoring is needed to assess where the risk for travelers is highest.

METHODS

To investigate where the risk for travelers to acquire typhoid fever is highest, 208 patients with typhoid fever and recent travel were matched with travelers' statistics collected by the Swiss Federal Office of Statistics.

RESULTS

At the beginning of the study period, up to 30 infections with Salmonella typhi were recorded per year in Switzerland. Since 2001, less than 15 confirmed cases per year occurred. A majority of the 208 (88.5%) typhoid cases were associated with recent travel. Countries with highest risk were Pakistan (24 per 100,000), Cambodia (20 per 100,000), Nepal (14 per 100,000), India (12 per 100,000), and Sri Lanka (9 per 100,000).

CONCLUSIONS

We found that over a 12-year period (1993-2004), the travel-associated risk of typhoid fever is highest for destinations in the Indian subcontinent. All other regions showed a decline, most markedly in southern Europe. Our results suggest that typhoid fever vaccination should be recommended for all travelers to countries in South Asia. Otherwise, vaccination of tourists to frequently visited low- and intermediate-risk areas is not necessary, unless there are behavioral risk factors.

Immunisation of the travelling child

As a direct consequence of the current increase in international mobility, a significant increase in family travel is occurring. Protection against vaccine preventable diseases in the travelling child plays a key role both from an individual and a public health perspective: pre-travel immunisation protects travelling children and, at the same time, prevents the importation of pathogens that can spread throughout the community. Children immunisation presents unique challenges in travel medicine practice: some vaccines cannot be given below a definite age for several reasons and altering the standard schedule of routine vaccines is sometimes needed to ensure early protection. Furthermore, the risk for some travel-related diseases is higher among children. The aim of this review is to analyse the main epidemiological and clinical aspects relevant to immunisation of travelling children and to provide travel medicine practitioners with a practical approach to this issue.

Spanish travelers to high-risk areas in the tropics: airport survey of travel health knowledge, attitudes, and practices in vaccination and malaria prevention

OBJECTIVE

To evaluate travel health knowledge, attitudes, and practices on vaccination and malaria prevention among Spanish travelers to the tropics.

METHODS

A cross-sectional survey was carried out in the departure lounge of the two main Spanish international airports in the summer of 2004. A questionnaire was administered to 1,206 Spanish citizens traveling to high-risk areas of tropical South America, 635 travelers (52.6%); Southeast Asia, 251 (20.8%); Sub-Saharan Africa, 181 (15.0%), and the Indian subcontinent, 139 (11.6%). Risk areas were defined according to published sources. Travelers were asked about their attitudes to travel vaccines and malaria prophylaxis and whether they had received either or both on this or previous trips. Adequate malaria prophylaxis was considered as the correct drugs for the destination as indicated by the World Health Organization.

RESULTS

Fifty-eight percent of travelers were male and the mean age was 38 years. Thirty-six percent were traveling to tropical areas for the first time. The main reason for travel was tourism (82%) or business (12%). The mean time preparing the trip was 39 days; 73% looked for information a mean of 19 days in advance and 54% were advised in travelers' clinics. Fifty-five percent received no travel vaccines. A total of 48.1% of tourists and 30.1% of business travelers were vaccinated (p<0.00006). The most frequent vaccines administered were as follows: typhoid fever, 32%; yellow fever, 29%; tetanus-diphtheria, 24%; and hepatitis A, 14%. Malaria prophylaxis was taken by 422 travelers including mefloquine (44%), atovaquone-proguanil (17%), chloroquine (16%), chloroquine-proguanil (15%), doxycycline (3%), and unknown (5%).

CONCLUSIONS

More than half of travelers to risk areas received no vaccinations before the trip. More than a third of travelers to Sub-Saharan Africa received no malaria prophylaxis.

Cases of typhoid fever imported into England, Scotland and Wales (2000-2003)

Although typhoid fever is no longer endemic in most of the developed world, it remains a major infectious disease in less developed regions and imported cases continue to occur in returning travellers, immigrants or migrant workers. We analysed all 692 isolates of Salmonella enterica subspecies enterica serovar Typhi from cases in England, Scotland and Wales that were sent to the Laboratory of Enteric Pathogens at the Health Protection Agency, Centre for Infections, London, UK between 2000 and 2003. The country of acquisition was known for 416 isolates (60%), and the majority of these (70%) came from India or Pakistan. Overall, 24 countries were listed, mainly in Asia and Africa. A total of 48 phage types were detected, 41% of which were Vi-phage type E1. Antimicrobial susceptibility testing revealed that 22% of isolates were multidrug resistant (MDR) (defined as resistance to chloramphenicol, ampicillin and co-trimoxazole) and 39% were quinolone resistant. A significant number of isolates (n=49) were sensitive to nalidixic acid by disk test but exhibited low-level ciprofloxacin resistance, suggesting a novel mechanism of resistance and reinforcing the need for minimum inhibitory concentration determination. Overall, 13% of isolates were both MDR and likely to show a poor response to a fluoroquinolone. A third-generation cephalosporin (e.g. ceftriaxone) should be considered as empirical therapy in regions of the Indian subcontinent where resistance is now at high levels as well as in patients returning from these areas. This study helps to describe the epidemiology of antimicrobial drug resistance in typhoid fever.

Special infectious disease risks of expatriates and long-term travelers in tropical countries. Part II: infections other than malaria

A wide range of viral, bacterial, and protozoal diseases pose risk to long-term tropical travelers. Risk varies geographically and with lifestyle. For some infections, risk increases with duration of stay, coming to resemble that of the local population. Risk management strategies include vaccination, chemoprophylaxis, avoidance measures, and screening, where appropriate. Vaccination against hepatitis A and B, typhoid, and rabies is recommended for all long-term travelers to (sub-)tropical areas. Lowering of the vaccination threshold for Japanese encephalitis is suggested. Meningococcal disease is rare in travelers, but vaccination is safe and acceptable. The efficacy of Bacillus Calmette-Guérin (BCG) is uncertain; immunological testing avoids BCG's confounding of tuberculin testing. Diarrhea is common, and self-treatment may be recommended. Sexually transmitted infections including human immunodeficiency virus (HIV) are serious risks; education, screening, and HIV postexposure prophylaxis following involuntary exposure are recommended. Many infections are chronic or asymptomatic, and appropriate screening is recommended on return or after prolonged exposure.

The comparative burden of salmonellosis in the European Union member states, associated and candidate countries

Background

Salmonella is an infectious agents causing numerous cases of illness each year, and thereby having significant economic impact. Using returning Swedish travellers we estimated the burden of salmonellosis in different European countries.

Methods

From the Swedish database on notifiable communicable diseases 15,864 cases with travel-associated salmonellosis acquired in Europe from 1997–2003 were retrieved. These cases were compared to a dataset from the same years on 14,171 randomly selected Swedish residents, with a history of recent overnight travel in Europe. Distribution of salmonellosis in returning travellers and the distribution of Salmonella Enteritidis was analysed for different member states in the European Union, associated and candidate countries. The risk of being notified with a salmonella infection after return from each European country/region was calculated, and compared with official reporting data rom these countries. Using Norway as reference country, we could 1) construct comparable incidence estimates and 2) calculate the "under-reporting" in each country compared to Norway.

Results

The highest burden of salmonellosis was estimated for Bulgaria (2741/100,000), followed by Turkey with 2344/100 000 and Malta with 2141/100 000. S. Enteritidis is the dominating serotype, 66.9 % of all cases and phage type 4 accounts for 37.5 % of the S. Enteritidis cases

Conclusion

Using returning tourists as a sentinel population can provide a useful base for comparison of disease burdens in different countries/regions. Focusing prevention of salmonellosis to prevention of egg and poultry associated S. Enteritidis infection will have a major impact from a public health perspective and will significantly lower the burden of disease in most European countries.