Update on Travel Medicine

Educational Objectives

The goal of this program is to improve the prevention and management of health problems for international travelers. After hearing and assimilating this program, the clinician will be better able to:

1. Counsel patients about preventive strategies in travel medicine.
2. Recognize and treat infectious pathogens in the travelers returning from tropical destinations.
3. Choose the appropriate pre- and postexposure prophylaxis for rabies.

Summary

Risks to travelers: motor vehicle accidents and violence are the leading causes of death in travelers; other risks include diarrhea, insect and animal bites, sexually transmitted infections, and emerging infectious diseases; GeoSentinel reports that most emerging infectious diseases come from animals (zoonosis); travel-related illnesses are primarily gastrointestinal, followed by fever (malaria [especially in sub-Saharan Africa], dengue), skin and soft tissue infections (including rare diseases, eg, cutaneous larva migrans), insect bites, leishmaniasis; allergic reactions are another risk

Travel-associated injuries: the study of travel-related illnesses is challenging because of demographic differences, time exposure, and underreporting; the proportionate mortality ratio compares the illnesses in travelers with those of the index population; travel itself is a risk, with ≈50% of travelers experiencing some type of injury (mostly trauma); traffic accidents, drownings, violence, homicide, and suicides also occur; cardiovascular disease is prevalent in travelers (especially in older age groups); the environment is a risk factor and can cause hypothermia and heat injuries in certain parts of the world; infections cause less mortality in travelers than trauma does; the estimated proportionate mortality ratio is approximately 1.4 to 3.3; risks — compared with natives, travelers to the European Union are at 9.4 times greater risk for road traffic accidents (RTA) and 15-fold more likely to drown; US citizens traveling abroad have a much higher drowning risk (significantly higher risk among men traveling to Mexico)

Road traffic accidents: are common in low- to middle-income countries; less safe vehicles, poor road conditions, motorcycles, and inadequate medical response contribute to the risk; the first responders in the United States (US) are skilled and quick, with updated protocols; a lack of a high level of care in some parts of the world leads to higher mortality rates at the scene

Pretravel evaluation: should occur ≥1 mo before travel to allow time for some vaccines, eg, typhoid, hepatitis A; can update routine vaccines; measles is an emerging risk because of decreased vaccination rates during the pandemic period; food and water safety should be addressed, eg, adventurous eating on camping trails; avoid mosquitoes and arthropods (many options are available to avoid bites and transmission of diseases)

Traveling with medicines: the medicines considered to be routine in one country may not be legal in other countries; for prescription medicines, carry the labeled bottle or a letter from the physician; be cautious with narcotics; the International Narcotics Control Board lists substances considered controlled in different countries; consult the embassy for more information; be cautious of counterfeit medications when buying medicines overseas (≈10% of medications are substandard or false, which may allow the disease to progress); insurance is not expensive and can save lives in cases of serious injury; global positioning system communications can be helpful while traveling; satellite phones are costly but should be considered for remote travel (to help avoid search and rescue activities); before travel, investigate risky sources and locations; in case of emergency, ensure transportation to definitive care in an appropriate-level medical center

Water purification: 2 recommended methods are the use of UV pens (eg, SteriPEN) and chlorine dioxide; boiling water is another option; the Centers for Disease Control and Prevention (CDC) recommends 3 min of rolling boil of water (to account for high altitude; 1 min of boiling is usually effective); most microorganisms die before the boiling point is reached; however, a rolling boil helps clean the container as well; halogens (chlorine dioxide), bleach, and bromine are effective methods; before sterilizing or purifying the water, decant or filter it; exposure to sunlight (UV) is a sterilization method and can significantly reduce Escherichia coli count; standing pond water is considered more sterile because of its constant exposure to the sun; 0.2 μm filters are commonly available; filters are effective (except for chemical contaminants and viruses) but tend to be heavy; smaller filter options (LifeStraw) can be used; chlorine dioxide tablets are small, lightweight, available in individually wrapped foil packs, difficult to destroy, and can withstand temperature extremes

Travel-associated infections: COVID-19 remains a concern; influenza is a sporadic disease (not seasonal) and can occur in warm climates; closed spaces on cruise ships create a high risk for influenza; Legionnaires’ disease (caused by Legionella), an autoimmune-compromised chronic lung disease, prefers cold temperatures (eg, ventilation systems in cruise ships, swamp coolers, cooling systems in hotels); norovirus, endemic to the Colorado River and many other water sources, is common and can be suspected in group outbreaks (treated only by management of symptoms)

Eschar-forming febrile illnesses: are common in travelers; anthrax is unlikely without catalytic exposure or bioterrorism; insect bites (usually on the legs) can cause scrub typhus; plague is still active in certain areas (eg, Colorado) but does not cause eschar; rickettsia can cause eschar; African tick bite fever — fairly common; Rickettsia africae is common in southern Africa and is closely related to Rocky Mountain spotted fever, which manifests with petechial rashes on the hands and palms; travel history and the presence of eschar are important for diagnosis; Rickettsiae are gram-negative bacteria carried by an insect (fever caused by R africae is reported as a spotted group fever)

Respiratory infections: ≤33% of travelers return with respiratory infections (especially influenza and colds), including COVID-19 and respiratory syncytial virus (an increasingly recognized pathogen); polymerase chain reaction (PCR) testing has allowed for the identification of these pathogens; usual management is typically appropriate; some pathogens provide epidemiologic clues; Streptococcus pneumoniae causes ≈40% of hospitalizations (close contact and respiratory spread); influenza can cause severe pneumonia, abscesses, and meningitis

Other infections: plague — endemic in some places (eg, Madagascar), with a high mortality risk if not treated properly; pneumonic plague is the main concern; hantavirus — common in the western hemisphere; caused by the Sin Nombre virus, which was recognized in the Four Corners area; the syndrome causes hyponatremia and severe progressive pneumonia and does not respond to antibiotics (ie, hantavirus pulmonary syndrome); Nipah virus — a bat-associated infection in Southeast Asia, has high mortality rates and can transmit from human to human (mostly close contact); others — HIV and tuberculosis (TB) are major issues in sub-Saharan Africa, with TB being highly communicable (especially in enclosed spaces); Legionella poses a risk in Eastern Europe, while the risk for the avian flu is associated with Central Asia; the risk for pertussis (whooping cough) persists; the differential diagnosis for pneumonia in returning travelers is broad and familiar unless there is an epidemiologic clue or abnormal clinical course suggesting otherwise

Eosinophilia: high eosinophil count is >500 cells/μL; >1500 cells/μL suggests something other than allergy; found in ≤10% of returning travelers; rule out allergic reactions first (eosinophilia can be caused by asthma or atopic skin disease); check for Strongyloides if there is an infection

Strongyloidiasis: affects a considerable number of people in the US (≤5% in some areas); these are nematodes, which are shed in the stool; they can penetrate the skin; the infection rate can be high in tropical areas; infection can persist for a lifetime in the host; it has an autoinfection cycle, with entry through the skin and spread to the gut and the lungs, it can cause a Loeffler syndrome-like appearance; suspect if a traveler has diarrhea and pulmonary infiltrates; unexplained gram-negative sepsis is another indication of strongyloidiasis (found even in endemic cases); it can cause gram-negative meningitis; the unexplained presence of multiple species of bacteria in the blood could be a clue

Diagnosis: is difficult; serology may show cross-reactions with other nematodes; multiple stool samples may be needed; check the history for gram-negative sepsis; hyperinfection syndrome has a high mortality rate (occurs mostly in immunocompromised patients and those taking steroids); steroids worsen strongyloidiasis; obtain serology to rule out strongyloidiasis before administering steroids

Schistosomiasis: is caused by a blood fluke that comes from cercarial snails, which penetrates the skin, disseminates through the liver, and then spreads to the lungs, liver, brain, and bladder; it can cause ulcers and bleeding; scarring and fibrosis in target organs can occur in people living in endemic areas or with long-term schistosomiasis; sub-Saharan Africa, the Middle East, some areas of the Philippines, and Indonesia are endemic areas; exposure to water and travel to these areas are diagnostic clues; treatment — includes praziquantel and steroids; obtain Strongyloides serology before treatment; redose in 2 to 6 wk; steroids prevent an exuberant inflammatory response; if pulmonary involvement is not treated, it can lead to hypoxic injury; serology and serum PCR results remain positive for a long time; stool and urine egg tests can be performed after 6 wk of treatment

Traveler’s diarrhea (TD): is common in travelers and is primarily caused by E coli; it can also be caused by Salmonella, Shigella, or Campylobacter infection, but most cases reflect a difference between the microbiome of the traveler and the natives of the location of travel; viruses can be the cause (eg, norovirus in cruise ships); only ≈10% of TD cases are protozoal (which mostly affects people who have been there for a long time); giardiasis is common and can affect animals

Treatment: bismuth subsalicylate (eg, Pepto-Bismol) — the first-line treatment for mild to moderate TD; available in individually wrapped foil packs (not heat- or cold-sensitive); can cause the tongue and stool to turn black; the salicylate component is associated with a mild bleeding risk; antibiotics — considered for red flags, eg, inability to eat, worsening condition, sepsis, true blood in stool, dehydration; fluoroquinolones can be used, but emerging resistance is a concern; ciprofloxacin is used in certain parts of the world; azithromycin is commonly prescribed (useful for travelers to carry because it can be used for multiple indications); risk factors — proton pump inhibitors (increase gastric pH); genetics may play a role; ≈10% of people have irritable bowel syndrome; persistent TD after treatment — may represent treatment failure, another infection, or the gut remaining irritated from the infection; may take months to resolve; people may develop lactose intolerance after infections; counsel about simplifying diet, retesting, retreating, or using another agent

Rabies: causes ≈100% fatality rate; it occurs everywhere except Antarctica; it is considered a neglected tropical disease; it is primarily caused by dogs outside the West and by bats, raccoons, skunks, and foxes in the West; vaccinations are common, but deaths also occur (often underreported); fatal encephalitis is the leading cause of death; the virus enters through the skin and spreads to the brain (can take from 1 wk to 1 yr); no routine diagnostic tools exist; patients with furious rabies may have frothing, spasms, hydrophobia, or aerophobia; animal contact is the clue; Guillain-Barré-type ascending paralysis can occur; vaccination and avoidance are recommended; the vaccine is expensive in resource-limited parts of the world (especially Southeast Asia); the World Health Organization (WHO) recommends reserving immunoglobulin for bites or contaminated mucous membranes

Preexposure prophylaxis: is indicated for adventurous or military travelers (consider what they will be exposed to and the duration of exposure); highly effective in humans and animals; human diploid cell culture or chick embryo cell culture rabies vaccines are available; 2 doses (on days 0 and 7); the response lasts for several years; intradermal vaccination is more immunogenic; a titer of 0.5 IU/mL provides 100% protection; the American College of Emergency Physicians and the Advisory Committee on Immunization Practices tables help risk-stratify the traveler or patient; consider boosting a titer if the person is revisiting the area after many years

Postexposure prophylaxis: is the most common rabies intervention; povidone-iodine is the preferred virucidal agent; the recommended dose of recombinant immunoglobulin is 20 IU/kg at the wound; if the patient has already received the vaccine, they need only 2 shots and do not need the immunoglobulin; if unvaccinated, give vaccines on days 0, 3, 7, and 14; day 28 vaccine is optional (should be given to immunocompromised hosts); safe during pregnancy

Emerging threats: avian influenza subtype A is highly pathogenic; all human cases have been contracted through close exposure (human, bovine, or birds [more commonly]); the spectrum of disease ranges from “regular flu” to encephalopathy and multiorgan failure; H5N1 virus — highly pathogenic to poultry and can infect humans through direct contact; it affects various birds and animals; no human-to-human transmission has been reported; studies show that even those who are exposed do not develop immunity; there is no antiviral resistance; some existing vaccines can be used if it emerges as a human pathogen; other avian-associated influenza viruses — have been associated with human-to-human transmission; global cases have slowed down but are rising again in the postpandemic era; H1N1 remains the most common influenza strain

Dengue: increasing incidence of infection, possibly due to urbanization and rising temperatures; increases in temperature are found to increase the infectivity of the mosquito; the CDC issued a level 1 travel notice for dengue; use precautions; expect more dengue in travelers (especially to Brazil and Cuba); transmitted by Aedes aegypti and Aedes albopictus (associated with yellow fever, Zika, and chikungunya); breeds near houses, especially in standing water; feeds during the daytime and may bite multiple times; found in latitudes between 45 degrees north and 35 degrees south; also known as break-bone fever; symptoms include headaches, eye pain, and rashes; can progress to dengue hemorrhagic fever (DHF; often fatal); there are 4 serotypes; immunity is transient, so reinfection is possible; the incubation period is fairly short; DHF — a widespread infection that causes disseminated intravascular coagulation and vascular permeability, leading to dengue septic shock; may increase hematocrit and decrease platelet count; spontaneous bleeding with the performance of the tourniquet test supports the diagnosis; no effective treatment is available; warmer temperatures affect mosquito behavior and habitat (cannot survive beyond certain temperatures); endemic dengue transmissions have occurred in the US; most frequently found in people from Hawaii, Texas, New York, and Florida; ≈5% of Key West residents are found to be dengue seropositive (vs the majority of people in India)

Prevention: the only vaccine for dengue fever has been discontinued (lack of use) but was effective; permethrin-impregnated clothing, bed nets, picaridin, and N,N–diethyl-meta-toluamide (DEET) are effective; lavender has been recognized as an effective mosquito repellent; picaridin is less effective than DEET

Monkeypox (Mpox): the WHO has issued a public health emergency of international concern; the Democratic Republic of Congo had >100 laboratory-confirmed cases of clade 1b Mpox virus (the other Mpox virus was clade 2 strain); ≈30% of infections are associated with sexual contact; nonsexual transmission can also occur; the reported mortality rate is ≈5% in adults and ≈10% in children; the new Mpox virus is more contagious (skin-to-skin contact)

Pearls: for any international travel, plan well ahead, obtain necessary vaccines, and check local conditions; carry medicines for TD, eg, azithromycin, loperamide (eg, Imodium, Imogen, Imotil), and some form of bismuth; be cautious while swimming in fresh water in some parts of the world

Readings

Gambini JM, Watkins E. Traveler’s diarrhea. JAAPA. 2023;36(11):1–4. doi:10.1097/01.JAA.0000979520.71733.bc. View Article; Guse CE, Cortés LM, Hargarten SW, et al. Fatal injuries of US citizens abroad. J Travel Med. 2007;14(5):279–287. View Article; Jose BP. Nipah: the deadly menace. J Acad Clin Microbiol. 2018;20(2):66–73. doi:10.4103/jacm.jacm_34_18. View Article; Kamath V, Ganguly S. Emergencies in dengue fever. APIK J Intern Med. 2024;12(3):135–140. doi:10.4103/ajim.ajim_92_23. View Article; Kare J, Roham T, Hardin E. Plague and anthrax: ancient diseases, modern warfare. Topics Emerg Med. 2002;24(3):77–87. View Article; Lewis T, Baack K, Gomez L, et al. Rabies post-exposure prophylaxis in the emergency department. Am J Emerg Med. 2024;78:202–205. doi:10.1016/j.ajem.2024.01.027. View Article; Mileno MD. Travelers and eosinophilia. Infect Dis Alert. 2008;28(3):30–32. View Article; Mouchtouri VA, Rudge JW. Legionnaires’ disease in hotels and passenger ships: a systematic review of evidence, sources, and contributing factors. J Travel Med. 2015;22(5):325–337. doi:10.1111/jtm.12225. View Article; Rolfe RJ, Ryan ET, LaRocque RC. Travel medicine. Ann Intern Med. 2023;176(9):pITC129–ITC144. doi:10.7326/AITC202309190. View Article; Wyler BA, Young HM, Hargarten SW, et al. Risk of deaths due to injuries in travellers: a systematic review. J Travel Med. 2022;29(5). doi:10.1093/jtm/taac074. View Article.

Disclosures

For this program, members of the faculty and planning committee reported nothing relevant to disclose.

Acknowledgements

Dr. Clover was recorded at When Things Go Wrong in the Outdoors, held August 15-16, 2024, in Government Camp, OR, and presented by the Oregon Health and Science University. For information on upcoming programs from this presenter, please visit ohsu.edu/school-of-medicine/cpd. Audio Digest thanks Dr. Clover and Oregon Health and Science University for their cooperation in the production of this program.

CME/CE INFO

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The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 2.00 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

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Lecture ID:

FP730101

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

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