Chapter 2 The Pretravel Consultation
Perspectives: The Need for a Cost Analysis to Justify the Travel Medicine Consult
CLINICAL BENEFITS OF THE PRETRAVEL MEDICAL ENCOUNTER
The pretravel medical encounter usually consists of 3 components—vaccination, prophylaxis, and education—each of which is intended to reduce the risk of illness during travel. Vaccination and prophylaxis prevent disease among travelers. Fewer data exist on the effect of pretravel education and advice. For example, educating travelers on ways to limit exposure to foodborne and waterborne diseases has not been shown to have a demonstrable effect on the risk of travelers’ diarrhea.
The pretravel encounter has more clinical benefit when the risks of acquiring a travel-related illness are greater. Such risks are influenced by regional destination, itinerary, travel duration, and season, but few data quantify the risk to travelers. Our best data for estimating disease risk at a destination often reflect disease prevalence among the local population and may not correlate with the risk to travelers. Vaccine efficacy data are also too often extrapolated from studies unrelated to travel. Travel-related risks fluctuate and are affected by evolving destination infrastructure and economy, advancements in disease-control programs, and the emergence of infections into new zones. The risk of travel-related illness is also traveler-specific. Some travelers participate in more high-risk behavior, and some travelers (such as those who are immunocompromised) may be more predisposed to infection or complications.
Benefits of a pretravel encounter may also extend beyond the immediate duration of travel, and immunity resulting from vaccination can overlap multiple itineraries. Travelers are known to spread extremely contagious infections (such as measles), highly morbid diseases (such as Middle East respiratory syndrome or Ebola), and highly drug-resistant pathogens (such as NDM-1– expressing bacteria or multidrug-resistant Mycobacterium tuberculosis). Reducing importations of communicable diseases by returning travelers can have far-reaching public health implications by diminishing outbreaks.
ECONOMICS OF THE PRETRAVEL ENCOUNTER
The pretravel encounter incurs direct costs, including clinic visit fees (as a component of a primary care visit or dedicated specialist visit), vaccines, and prescribed drugs, as well as indirect costs associated with travel to clinic and missed work. When considering costs and other components of resource use, it is essential to consider the perspective of who pays and who benefits: the traveler, the health care payer, or society.
Economic benefits include when the pretravel encounter prevents a travel-related illness; therefore, costs of the travel-related illness prevented should be considered as cost savings. A frequently overlooked economic aspect linked to the pretravel medical encounter is its potential to reduce the incidence of many travel-related illnesses that have public health implications. The introduction of measles or hepatitis A into a community by a returning traveler prompts expensive public health and infection-control responses. Such costs are largely borne by the public health sector and therefore do not usually appear in the financial calculus of the individual traveler or the insurance carrier.
MATHEMATICAL MODELING FOR TRAVEL MEDICINE
Mathematical modeling allows for a comprehensive investigation of the value of the pretravel medical encounter. By incorporating best estimates of benefits and costs for pretravel encounters, travel exposures, and travel-related illness, a model can project possible outcomes and costs for different travelers, exposures, risks of infection, and effectiveness of pretravel interventions singly or in combination.
A comprehensive model of the pretravel encounter would examine the range of possible illnesses posed by an itinerary, including those that present long after return (such as tuberculosis or HIV) or that lead to chronic sequelae (such as neurologic damage from cerebral malaria, Japanese encephalitis, or Zika infection). Such a model would incorporate the effect of any pretravel intervention on mitigating the risk of infection while traveling as well as possible side effects of the intervention. Models should incorporate the costs of public health–related resources and expenditures relating to the importation of pathogens, not only to trace and limit ongoing disease transmission but also to mitigate the risk of establishing environmental or animal reservoirs in home communities. Such a model could then be used to examine the effect of a pretravel encounter on different populations of travelers. Because only some travelers seek pretravel evaluation, a model could examine the effect when different percentages of the traveling population obtain pretravel evaluation.
A modeling approach can also be used to perform sensitivity analyses, in which a range of values for a specific input parameter is examined in terms of the impact on the outcome of interest. Sensitivity analyses can evaluate thresholds, or the specific value at which a parameter results in a meaningful change in clinical outcomes or costs. Uncertain data estimates or assumptions are assessed by using a model in a similar fashion, investigating at what values such estimates will result in clinically meaningful changes. Results from a pretravel model could highlight where further data would be high-yield and worth investing research dollars.
A logical way forward is to begin by focusing initial analyses around a number of core areas. Studies have been published that investigate a specific component of the pretravel encounter, including malaria prophylaxis, hepatitis A vaccination, typhoid vaccination, and travelers’ diarrhea strategies. Unfortunately, many of these analyses were performed decades ago. A reasonable approach would therefore be to develop modeling approaches for major groups of travel-related illnesses, using available current data regarding the pretravel encounter from the GlobalTravEpiNet (GTEN) consortium (see Chapter 1, Travel Epidemiology) and other large consortiums. The goals of such analyses could include defining core metrics for pretravel encounters, improving the value of pretravel encounters, and examining where improvements in pretravel medicine would result in maximally improved patient outcomes and cost-effectiveness. These separate models could then be incorporated into a single integrated analysis that would address a comprehensive pretravel encounter. Such an approach will not be easy, but it is necessary.
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Perspectives sections are written as editorial discussions aiming to add depth and clinical perspective to the official recommendations contained in the book. The views and opinions expressed in this section are those of the authors and do not necessarily represent the official position of CDC.
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