ARCHIVED - AN ASSESSMENT FOR THE DEVELOPMENT OF A NATIONAL SURVEILLANCE SYSTEM FOR TRAVEL-ACQUIRED ENTERIC DISEASE

Introduction

The most common medical problem affecting Canadian travellers to other countries is diarrhea^(1,2). Destinations with developing economies, particularly those with semitropical or tropical climates, are of greatest concern. Surveys conducted by other developed countries indicate that between 25% and 40% of travellers returning from trips abroad experience gastrointestinal illness^(3,4). However, the risk of travellers' diarrhea is not uniform and, depending on the country of destination, type and duration of travel, and the definitions used to identify cases, attack rates as high as 70% have been reported^(1,5,6). Travel-acquired enteric disease (TAED), especially of an infectious nature, continues to be a concern because of the following factors:

• large, modern resorts constructed in developing countries with inadequate physical and public health infrastructures to secure clean water and food;
• contamination of water used for recreational purposes by tourists (i.e. inadequate sewage disposal);
• risk behaviours among tourists such as non-adherence to safe drinking water practices and consumption of raw/undercooked food despite warnings;
• an increasing number of older and/or immunocompromised holiday travellers.

As part of its mandate to control and prevent enteric disease among Canadians, the Foodborne, Waterborne and Zoonotic Infections Division (FWZID), within the Centre for Infectious Disease Prevention and Control of Health Canada, has a responsibility to understand the burden of illness associated with travel abroad and must be able to recognize and respond to emerging infectious diseases or clusters of infection imported through travel. There have been attempts to quantify the contribution of travel as a risk factor for enteric illness. For example, the National Studies on Acute Gastrointestinal Illness Travel Pilot Study found that of the 55/652 respondents with acute gastrointestinal illness in the defined study period, six (11%) had travelled outside Canada within the 4 weeks before their symptoms began⁽⁷⁾. As well, a matched case-control study done in 1999-2000 identified travel outside Canada as an independent risk factor for sporadic gastroenteritis due to Salmonella Typhimurium⁽⁸⁾. Currently, however, there is no national structure for systematically capturing travel information on cases of enteric disease.

To improve our own surveillance of TAED, the experiences and expectations of other jurisdictions within Canada and abroad were sought. This was, in part, instigated by a previous FWZID investigation regarding gastroenteritis among Canadian travellers⁽⁹⁾. The present article summarizes these findings and the results of a literature review. Together, they provide a framework for the development of a TAED surveillance system that will enable Health Canada to identify, manage, and report these illnesses.

Methods

Three approaches were undertaken for the purpose of identifying TAED surveillance needs and best practices within and outside Canada. International practices were identified through a survey of colleagues in other countries with similar mandates for enteric disease surveillance. A second survey of provincial and territorial health ministries gathered information regarding current travel surveillance practices and the perceived needs and priorities for TAED. Finally, a literature review was conducted to identify TAED surveillance systems and solutions used elsewhere.

International Survey

The study was conducted in two phases, the first in the fall of 2001 and the second in the fall of 2002. Each phase addressed different groups of international contacts who were identified by colleagues within FWZID or from published journal articles. A three-page questionnaire with a cover letter explaining the survey's purpose was mailed electronically, and participants were asked to complete and return it within 2 weeks. Questions focused on the operation of the surveillance system as well as the respondent's opinion of the effectiveness of the system for the capture of travel-related information.

Provincial/Territorial Survey

The provincial/territorial (P/T) survey was administered between February and June of 2003. Colleagues within FWZID selected P/T contacts working in infectious disease surveillance at the ministries of health. The survey was conducted by telephone. If time was a factor, a copy of the survey was sent either by facsimile or electronic mail. Questions focused on the operation of their reporting system for travel-acquired illness in general, and what Health Canada's roles and responsibilities should be with respect to TAED.

Literature Review

The literature search was done using the National Center for Biotechnology Information PubMed database. Search terms used included travel medicine, surveillance, travel surveillance, enteric infections, and enteric disease surveillance.

Results

International Survey

In total, 28 international contacts were made in North America, Europe, and Australia/Oceania. Thirteen completed the questionnaire. One respondent's system did not collect travel information, so this response was excluded. Thus, the analyses were based on the responses of 12 individuals in 10 different countries. All 12 responses involved unique surveillance systems.

Surveillance system description

Of the 12 respondents, 11 work with surveillance systems that monitor enteric infections. The twelfth system was specific to travel-acquired infections; these results were kept because valuable information regarding TAED could be provided.

From the nine responses providing a system description, the most common enteric pathogens monitored were non-Typhi Salmonella (n = 9), Salmonella Typhi (n = 5) and pathogenic Escherichia coli (n = 5). Other organisms under surveillance include Shigella spp., Campylobacter spp., S. Paratyphi, Vibrio cholerae and other Vibrio spp., Yersinia spp., Listeria spp., Plesiomonas shigelloides, hepatitis A, Giardia lamblia and Entamoeba histolytica.

Data collection

In eight of the surveillance systems, the data collection form specifically addressed travel history. This tended to improve collection of travel data compared with systems that did not directly ask for this information. Travel destinations by country and dates of travel were most commonly reported (Table 1). All systems collected case-level information (whether travel-related or other), and three also collected information at the incident/event level (e.g. number ill following exposure to a travel destination).

Most systems receive reports from laboratories (n = 10) or physicians (n = 5). Five of six participants who were asked indicated that their system requires laboratory confirmation before a report is accepted.

Table 1. Case information collected by surveillance systems of other countries

Uses of data

The most common uses of the data included outbreak identification (n = 5), monitoring trends of TAED (n = 4) and incident investigation (n = 3). Although all 12 systems collect travel-acquired infection data, only eight publish or report their findings.

Nine of the surveillance systems are involved in collaborations with other agencies, all of which are multinational. Eight respondents indicated that their system has a process to report travel-related events back to the country where exposure is thought to have occurred. Factors that would prompt this type of communication include the following: a serious event, given the type of pathogen or the large number of reported illnesses (n = 4 each), an outbreak of two or more cases in travellers (n = 3), a clearly identified source (n = 1), or good potential for controlling disease spread (n = 1).

Effectiveness

Eleven of the participants responded to questions about the effectiveness of their system (Table 2). In general, the consensus was that identification of ill travellers was consistently problematic, but identification of and response to events such as outbreaks were handled in a better manner. Selecting those who provided the most "all of the time/some of the time" responses to the perceived effectiveness question allowed for three systems to be subjectively grouped as "better than most" according to the following characteristics: (1) active surveillance of TAED with data collection forms that address travel history; (2) direct involvement of physicians/clinicians in the reporting system; (3) periodic published reporting of TAED; and (4) established communications mechanisms in place.

Table 2. International survey: perceived effectiveness of surveillance systems in other countries (N = 11)

Provincial Survey

All 10 provinces and three territories were contacted. Responses were recorded for nine provinces and three territories. Instead of answering the survey in full, two respondents called or sent in a short commentary to address the questions asked.

Surveillance system description

Most provincial and territorial offices are informed of TAED events by regional health authorities or public health officials (n = 8). One is informed by medical laboratories, and one has decided to use a federally supported Website known as CEOSC (Canadian Enteric Outbreak Surveillance Centre) as its source of information. Most of the events are captured routinely and reported to the provincial and territorial offices in electronic or paper format.

When enteric diseases are acquired through travel, the provinces and territories are most concerned with the number of cases (n = 8) and the severity of the disease (n = 7). Salmonella (n = 8), Shigella and Campylobacter (n = 4), and Vibrio, Entamoeba histolytica and hepatitis A virus were the pathogens responsible for most of the cases of TAED in the provinces/territories. With regard to severity of disease, non-Typhi Salmonella (n = 4) was of most concern, followed by E. coli O157:H7 and Shigella (n = 3), S. Typhi and hepatitis A virus (n = 2), and Campylobacter and V. cholerae (n = 1). Mexico was the travel destination of greatest concern (n = 7), followed by the Dominican Republic (n = 6), the Caribbean in general and Cuba (both n = 2).

The P/T offices would inform Health Canada of TAED if the number of cases was of concern (n = 3), if a resort, cruise ship, or tour group was involved (n = 2), or an outbreak was suspected (n = 2).

Data collection

Regional health authorities conduct investigations associated with TAED, and records of the investigations are maintained within local files. Data regarding travel are collected using questionnaires on generic infectious disease. Once these data have been collected, they are added to a data file that contains all the information regarding the case. The travel data can be extracted from the file on an "as-needed" basis. Local authorities do not have a travel-specific data file. The pieces of travel information that are most often collected are the destination (n = 11) and date (n = 10) of travel. Other data items include information about related cases (n = 9), resort information (n = 8), airline information, food history, and immunization history (all n = 2).

Expected roles and responsibilities of Health Canada

Provinces and territories felt that the distribution of information about TAED at the national level should primarily be the responsibility of Health Canada. The lack of a standardized process for surveillance of travel-acquired enteric illness was an identified concern for many. It was felt that the principal federal responsibilities should include a specific TAED surveillance system; international communications, and coordination of meetings and outbreak investigations; the sharing of information with travel agencies; and the provision of protocols for the proper response and reporting of events at P/T and national levels. If these were undertaken, the issues of identification, underreporting, and prevention of travel-acquired illness would be better addressed and Health Canada's collaboration with the provinces and territories enhanced.

Other anticipated federal functions include targeted surveillance of more serious and/or emerging pathogens usually acquired through travel, identification and monitoring of high-risk destinations, public education/advisories, determination of the burden of illness due to TAED in Canadians, and prevention of TAED through capacity building with other countries.

Literature Review

Although travel is mentioned in the literature as a component of multiple surveillance systems^(10-22), this represents a small portion of all analyzed papers. Most of the systems discussed were national disease surveillance systems based on notifiable disease or laboratory-based data^{(10,13,14,18,23)}. Those that did focus on travel-acquired infections tended to be sentinel systems^(12,22) and/or did not capture enteric disease events^{(10,13,16,20,21)}. Regardless of the type of system, the common assumption is that afflicted individuals will be motivated to seek medical attention of some sort.

In several publications the view was expressed that visits to emergency departments, travel medicine clinics, and airport quarantine stations should be incorporated into travel-acquired disease surveillance^{(14,15,19,24)}. Two of the systems listed, EMERGEncy ID NET (emergency departments) and Geosentinel (travel medicine clinics), are based in the United States. The latter also involves a small number of travel clinics in other countries, including one in Canada. The Traveller's Diarrhoea Network in Japan integrates two quarantine stations, three infectious disease hospitals, and the Infectious Diseases Surveillance Center by electronic mail. It has been credited with promptly detecting outbreaks and causative food sources⁽¹⁵⁾.

Another concept is the practice of linking systems from several countries into multinational "meta-surveillance systems"^{(10,14,17,21,22)}. Geosentinel, TropNetEurop and Salm-Net are examples. The resulting benefits include the facilitation of communication and aid with outbreak investigations.

A common theme is the benefit of integrating multiple types of surveillance systems, including laboratory, sentinel, and notification systems, as well as conducting case-control studies^{(10,11,13-16,18)}. On its own, each system has limitations that may be offset by the strengths of another. For example, laboratory-based networks may not include risk factor information that could be found in another, adjunct system⁽¹³⁾.

The ability to estimate disease incidence in populations by risk factors such as travel can be problematic for all surveillance networks⁽¹¹⁾. Sentinel systems, by their nature, serve only a portion of a population. Systems based in hospitals will only capture very ill cases. Travel medicine clinics may see very few, if any, returning travellers since these individuals are more likely to visit their family doctors' office if they are ill. This is especially problematic for enteric diseases, which are frequently underreported and, although often travel-acquired, resolve prior to the completion of travel. However, such systems do offer benefits. Sentinel systems may employ health professionals who have greater motivation to collect risk factor and travel information. Therefore, travel information is more likely to be consistently obtained from these locations.

Discussion

These studies were undertaken in order to assist Health Canada to identify needs and methods for improving surveillance of TAED in Canada. Three important aspects of a surveillance system are that it (a) enables action (including control efforts), (b) allows for analysis and reporting, and (c) involves partnerships^(25-27). For a surveillance system to enable action, it needs to be timely and sensitive, and to collect high-quality data. Therefore, any enhanced surveillance system that Health Canada develops needs to emulate the systems that best meet these requirements.

From the international survey, we learned that system sensitivity is an issue. Whether identifying all travellers who become ill or only those who become ill upon returning home, the majority of respondents (seven of 11) felt that their system was not capable of the task. Tourists returning home to several different countries (or even provinces/states) from a common vacation destination may not trigger an increase over the expected for any one region but, collectively, may signify a concern in a travel destination. The need for multinational (or multiprovincial) cooperation and communication must also be addressed. Of the international colleagues asked, six indicated that they were involved in multinational collaborations. The most common are Enter-Net and the European Union Early Warning System; however, one of the systems, TropNetEurop, is a Europe-wide sentinel system established to monitor non-enteric travel-acquired diseases.

Canada's current notifiable diseases surveillance system involves the submission of reports by physicians and/or laboratories to local health authorities (e.g. public health units). These authorities are often part of P/T communicable disease surveillance systems, which in turn may be linked to national networks. Data fields for travel information, such as destinations and dates, are currently available in many of these systems. Unfortunately, such information is rarely entered(28). Gaps in Canada's TAED surveillance, such as the identification of ill travellers (upon return or while abroad), are shared with other countries. Other national systems were most effective for identification of and response to critical events, but less so with respect to the capture of pertinent information. These same parameters must be considered when strengthening the infrastructure of the Canadian system. Characteristics of surveillance systems that are associated with increased effectiveness include (1) active surveillance for TAED, including periodic reports; (2) direct involvement of physicians/clinicians in the reporting system; and (3) mechanisms for communication of events, when appropriate, back to the country of original exposure.

Recommendations offered by P/T respondents for the improvement of Canada's TAED surveillance practices include improved distribution of information at a national level, increased international communication and response coordination, and enhanced surveillance. Provinces and territories also expressed a desire for greater clarity of process, acknowledging the need for protocol development. In this way, the roles and responsibilities within public health networks for responses to and reporting of TAED would be clearly outlined. This would also address the roles of the different departments within Health Canada. Additionally, P/T respondents agreed that there is a need for enhanced national surveillance of TAED that would improve the capacity for an "action-oriented" response.

Published reports offered few examples of surveillance systems addressing TAED in a comprehensive, systematic manner. Generic approaches are identified in the literature in order to improve action-oriented surveillance systems overall. One important recurrent theme is the need for the integration of multiple methodologies within a system, including the linking of epidemiologic and laboratory information. Consequently, to maintain timeliness, it would be necessary to maximize the capacity of the system's laboratory component(s).

Options for improving the timeliness of reporting TAED events were identified. Activation of a travel alert Website for public health authorities would enable front line responders to submit more detailed TAED event information to Health Canada while simultaneously informing other public health authorities, and potentially travel medicine specialists, of events that may have also affected travellers returning to other parts of Canada. The CEOSC currently operates as a notification system for enteric disease outbreaks with secured access to public health authorities across Canada. Enhancements to CEOSC, or creation of a CEOSC-like Website, have been suggested. Since most travel medicine clinics focus on pre-travel consultation and education, this would allow them to be especially diligent with advice regarding specific infectious agents and exposures. As well, this type of information would help to accelerate routine responses to TAED by informing Health Canada and local investigators early in the course of an event, and could also be used to activate an escalated response to new and emergent issues brought to Canada through travel.

Surveillance programs with automated data transfer are more amenable to timely data submission and may motivate front line public health agencies to participate^(11,29). Internationally, only one system used automatic electronic download, and the specialized travel surveillance system included an option for automatic transfer by electronic mail.

System sensitivity must also be addressed, consideration being given to the possibility of compromised timeliness with increased sensitivity. A smaller system composed of travel medicine specialists may be more likely to gather travel information on a consistent basis⁽³⁰⁾. However, a limitation of such a system is that the relatively few travellers who seek medical attention after travel usually see their family doctors rather than travel medicine specialists. Therefore, the resulting information may apply to only a very small proportion of travellers. As well, it would not be possible to quantify the impact of the burden of illness associated with travel.

"Healthcare-by-phone" is an emerging method that could contribute to the identification of and improved data capture for TAED(11,29,31,32). Telehealth surveillance is proposed as timely and inexpensive. Syndromic surveillance may also have an application in Canada, as FWZID enhances the capacity of its Alternative Surveillance Alert Project (ASAP) program. However, because of the symptom-based nature of these two approaches, pathogen information would be more difficult to obtain; a laboratory-confirmed pathogen is the most essential requirement for any international notification or communication.

Conclusion

Health Canada is currently deliberating on the ways in which the information gathered in this series of studies can be used to enhance the nation's TAED surveillance and response programs. The development of a travel surveillance and response protocol for TAED is one option jointly under consideration by FWZID and the Travel Medicine Program (within the Centre for Emergency Preparedness and Response). Again, the intention is to augment current practices in the context of what is most effective while also addressing the needs as identified by P/T stakeholders. Communication of the roles and responsibilities of Health Canada and other public health authorities for TAED will be a major contribution to the overall endeavour.

Acknowledgements

The authors thank the following for their assistance: M. Bodie-Collins, Travel Medicine Program, Health Canada; Dr. L. Panaro, Canadian Field Epidemiology Program, Health Canada; Dr. P. Sockett, Foodborne, Waterborne and Zoonotic Infections Division, Health Canada; and the international and provincial/territorial survey participants.

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Source: CL Bowman, MHSc, and RL Finley, BSc, Foodborne, Waterborne and Zoonotic Infections Division, Centre for Infectious Disease Prevention and Control (CIDPC), Health Canada, Guelph, Ont; AU Chandran, MD, Foodborne, Waterborne and Zoonotic Infections Division, CIDPC, Health Canada, Guelph, Ont, and Canadian Field Epidemiology Program, Health Canada; S Isaacs, MSc, Foodborne, Waterborne and Zoonotic Infections Division, CIDPC, Health Canada, Guelph, Ont.