Travel-related illness.

An article about emerging pathogens would be remiss in not discussing travel-related illness (TAI). As of 2010 it was estimated that nearly 940 million tourists arrived at international destinations, which is twice that of 1990.1, 2 Of note, journeys to developing regions represented 47% of travel in 2010 compared to 31% in 1990. Given that the burden of disease, especially infectious diseases, remains high in the often impoverished developing world, it is not surprising that more than half of international travelers to developing countries become ill during their trip according to a study, and approximately 8% seek medical care for TAI during or after their journey.1, 2, 3, 4 Not unexpectedly, there are changes in the type of TAI reflective of the changing destinations—from tourism to work and destination-based travel, and the local, endemic illnesses found therein. The most common sites for contracting malarial illness, the most common TAI in a study, were sub-Saharan Africa (77%) and Oceania (6%).1, 2 Giardiasis and dengue fever were the second and third most commonly diagnosed TAI, respectively. Of note, gastrointestinal illness represented ~25% of diseases, and febrile or viral syndrome caused about 10% with respiratory syndromes affecting about 5% of TAI patients. These data are not unexpected given travelers often spend upward of 7–17 h in close proximity during airline travel. Even with improved ventilation and air turnover in modern jet travel, the small distance between and prolonged exposure to people make travelers vulnerable to respiratory and other infections. Financial considerations impact airlines; it is obvious to any frequent flier there remains a lack of proper between-flight cleaning of surfaces (seatback trays, lavatories, and arm rests), which increases the likelihood of disease transmission. Frequent hand washing, avoiding touching nose, mouth, and eyelids are important basic approaches travelers can take to reduce risk, as well as proper vaccination.

Adding to the challenge of characterizing and quantifying the extent of and patterns associated with TAI is the lack of data. Studies about travel-associated illness, including the medical response to TAI, are limited. Nevertheless, some disturbing results have been published. Data suggest that among patients who presented to an ED with symptoms consistent with a potential TAI, and who were eventually diagnosed as such, less than 10% were asked about travel at their first presentation to the HCF, resulting in delayed diagnosis, delayed treatment, and unnecessary patient discomfort.6, 7 We can do better.

One of the few, recent, and large-scale TAI studies involved over 40,000 ill travelers.1, 2 It revealed the most common destinations were sub-Saharan Africa (26%), Southeast Asia (17%), South-central Asia (15%), and South America (10%). And noted increases in enteric fever and dengue TAI.

International travel, the expansion of transnational business enterprises, growing reliance on imported goods, including food, all continue to raise the likelihood that infectious diseases, as well as the vectors that spread them, will enter the United States, remain, and pose significant public health challenges.1, 2, 3, 4, 5, 6, 7, 8, 9 Diseases that have historically been confined to regions, even continents can now spread with relative ease. Given the globalization of commerce, agriculture, tourism, and the job market, raising awareness, improved surveillance, and greater collaboration must go beyond traditional public health to include nonmedical resources and partnerships.

Although many of us were taught in medical school and residency training that when you hear hoof beats, think horses, not zebras, such advice must now be called into question, considering global travel, immigration into the United States from countries with endemic illnesses not commonly found in North America, and societal factors (domestic and international) that include poverty, homelessness, institutionalization, overcrowding—in health care facilities as well as domiciles—and lack of access to timely health care, all of which set the stage to create conditions that facilitate the spread of diseases that are from previously unknown, little recognized, or emerging pathogens that are endemic to or novel strains in foreign lands, and which can become very quickly clinical realities and community-wide problems in the U.S. This is one of the reasons obtaining a thorough travel and occupational history from patients who present with an atypical or severe, progressive illness, is critically important, as it may give valuable insights into the origin of the infection, how to access timely information from sources experienced in treating the cascade of symptoms (biodrome) (Fig.) and the etiological pathogen, and allow you to rapidly initiate appropriate, potentially life-saving interventions.

As WHO notes in its International Travel and Health updates,1, 6, 7, 9, 10 international travelers are at risk depending upon the area visited, the purpose of the trip, itinerary, resources, accommodations, hygiene, sanitation, and individual behaviors, as well as innate immunity and vaccinations, but unfortunately such pretravel guidance is lacking.1, 11, 12 General precautions can reduce the risk of exposure to infection risks. The most common infectious illness to affect travelers is “traveler's diarrhea”—of which many food and waterborne pathogens can be implicated. Knowing the modes of infectious disease transmissions provides opportunities for prevention. These include the following:

Food-borne (e.g., avoid raw or undercooked foods)

Waterborne (e.g., ice cubes, local water at restaurants, as well as standing water, and rivers)

Zoonoses (e.g., animal sources)

Sexually transmitted diseases (STDs) (e.g., local brothels)

Blood-borne [including poorly cleaned medical instruments as well as IV drug use (IVDU)]

Airborne (respiratory) (crowds or persons exhibiting respiratory signs/symptoms)

Soil [farms and farm lands can spread disease—footwear can carry soil/feces/animal products, and proximity to animals (e.g., avian influenza), plants (carry insects, for example) contributes to disease spread]

Respiratory diseases are common community-acquired diseases, as well as TIA; viruses creating epidemics of more severe viral pneumonitis, as was seen when a new coronavirus—SARS—continued to emerge.8, 13 Typically coronaviruses cause low-grade respiratory infections. That changed in 2002. By 2003, the World Health Organization (WHO) emphasized the importance of travel history in identifying possible and probable cases—a critically important step in characterizing the epidemiology and ultimately containing the infection. Soon thereafter, SARS coronavirus seemed to disappear, only to have another novel one appear in 2012; MERS CoV. Unlike SARS that emerged from Asia, MERS seems to have originated on the Saudi Peninsula in the Middle East.

It is important to note that several illnesses endemic abroad have a variety of incubation periods. Health care professionals should encourage their patients to discuss travel plans and/or work out of the country, be knowledgeable about travel specialists in their community as important pretravel resources and referral, as well as some of the more common TAI and emerging global threats. This includes infectious mononucleosis (IM) from Epstein–Barr virus and IM-like syndromes (cytomegalovirus—CMV) that have been reported in febrile travelers returning from the tropics.

It is important not to forget our servicemen and servicewomen deployed in developing nations—a unique source of TAI to be sure, who will return from the Middle East and other countries that may harbor endemic illnesses that U.S. physicians and health care professionals may be unaware of or unaccustomed to recognizing, let alone treating. As described elsewhere, but worth repeating, malaria is one of the most important infectious diseases of concern for returning military as well as travelers, especially in the Middle East, where our troops are deployed.

In anticipation of our troops returning from the Persian Gulf, Afghanistan, and elsewhere, it is important to take some time for training and familiarize ourselves with pathogens and symptom cascades—biodromes—that are likely to infect them.

At a minimum, patients presenting with respiratory or gastrointestinal illnesses, especially an unusual or unexpected cascade of symptoms, require a thorough history of travel and contact information to be obtained. An index of suspicion as well as travel, contact, and occupational history are all critically important pieces of information to aid in developing management strategies, especially if the infectious agent is not known or clearly identified.