International travel connects people with new destinations, but it also changes exposure to infectious disease, injuries, altitude, and crowded travel environments. These statistics from the CDC, WHO, IATA, and UN Tourism show the scale of common and serious travel-health concerns, as well as the continuing growth of international travel.
Contents
- Travel volume and common illness
- Malaria, dengue, and enteric fever
- Vaccination and vaccine-preventable disease
- Cruise ship and travel injuries
- Rabies and Japanese encephalitis
- Altitude illness and oxygen exposure
Travel volume and common illness
The number of people crossing borders helps explain why travel health remains a practical concern. UN Tourism estimated 1.4 billion international tourist arrivals in 2024. The organization said international tourism had recovered to 99% of its pre-pandemic level that year. IATA reported that international air passenger demand rose 10.4% from 2023 to 2024, while international full-year air traffic increased 13.6%. International air traffic was 0.5% above its 2019 level, and the full-year passenger load factor reached 83.5%, including an 83.2% load factor for international services. UN Tourism and IATA
Travelers’ diarrhea is one of the most frequent health problems associated with international trips. The CDC Yellow Book gives an attack-rate range of 30% to 70% during a 2-week period, depending on destination and season. Bacteria account for at least 75% to 90% of cases. Intestinal viruses account for at least 10% to 25% of illnesses, while protozoal pathogens account for approximately 10% of diagnoses, particularly among longer-term travelers. These ranges describe different parts of the illness picture and should not be added together as a single total. CDC Yellow Book: Travelers’ Diarrhea
Timing matters for travel preparation. Last-minute travelers can represent up to 16% of a travel clinic population, according to the CDC Yellow Book. In the same source, immunocompromised people are estimated to make up 6% of the U.S. population but account for about 1% to 2% of patients seen in U.S. travel clinics. Clinic attendance therefore does not represent the full population of people who may need individualized travel-health advice. CDC Yellow Book: Last-Minute Travelers and Immunocompromised Travelers
Malaria, dengue, and enteric fever
Mosquito-borne disease creates a sharp difference between global disease burden and the number of cases diagnosed in the United States. About 2,000 malaria cases occur each year in the United States, and almost all are imported. The CDC reported 2,048 U.S. malaria cases in 2019 and 602 in 2020. In 2023, it reported 10 locally acquired mosquito-transmitted malaria cases from four U.S. states. Globally, WHO reported about 263 million malaria infections in 83 countries in 2023 and approximately 597,000 deaths that year. CDC Yellow Book: Malaria and WHO World Malaria Report 2024
Visiting friends and relatives, often abbreviated VFR travel, is especially important in U.S. imported-malaria statistics. Approximately 75% of imported U.S. malaria cases occur among VFR travelers, even though VFR travelers make up less than 15% of the U.S. foreign-born population. This comparison concerns the distribution of imported cases and the foreign-born population; it is not a risk rate for every VFR traveler. CDC Yellow Book: VFR Travel
Dengue is also widespread. Estimates reach 390 million dengue infections per year worldwide, including about 96 million symptomatic cases. Dengue is present in more than 100 countries and destinations. From 2010 through 2021, the United States reported 7,528 travel-related dengue cases; 3,135 required hospitalization and 19 deaths were reported. Travel-associated case counts exceeded 1,400 in each year from 2019 and 2022 through 2024, compared with a previous peak of 919 cases in 2016. CDC Yellow Book: Dengue
| Condition or measure | Reported statistic | Geography or period |
|---|---|---|
| Malaria infections | About 263 million | 83 countries, 2023 |
| Malaria deaths | About 597,000 | Worldwide, 2023 |
| Dengue infections | Up to 390 million | Worldwide, annual estimate |
| Symptomatic dengue cases | About 96 million | Worldwide, annual estimate |
| Typhoid cases | About 9.2 million | Worldwide, annual estimate |
| Paratyphoid cases | About 3.8 million | Worldwide, annual estimate |
Typhoid fever causes an estimated 9.2 million cases globally each year, while paratyphoid fever causes an estimated 3.8 million. Together, the diseases cause an estimated 133,000 deaths globally each year. The United States reported about 450 culture-confirmed typhoid cases and about 130 paratyphoid A cases in 2019. During 2020 and 2021, U.S. reporting was roughly 150 to 160 typhoid cases and 30 to 50 paratyphoid A cases per year. CDC Yellow Book: Typhoid and Paratyphoid Fever
About 85% of U.S. typhoid cases and 80% of U.S. paratyphoid cases occur among international travelers. More than 70% of U.S. travel-associated enteric-fever cases are in travelers returning from South Asia. In 2020, VFR travelers accounted for 48% of U.S. typhoid cases and 64% of U.S. paratyphoid A cases. Among VFR cases that year, 84% of typhoid cases and 88% of paratyphoid A cases were linked to travel to the Indian Subcontinent. CDC Yellow Book: Typhoid and Paratyphoid Fever and CDC Yellow Book: VFR Travel
Vaccination and vaccine-preventable disease
Yellow fever illustrates how vaccination timing can matter before departure. WHO says yellow fever vaccination provides immunity within 1 week in 95% of vaccinated people, and a single dose provides lifelong protection. WHO also says four yellow fever vaccine manufacturers are currently prequalified. The CDC reports mild systemic symptoms in 10% to 30% of vaccinees. WHO: Yellow Fever Vaccines and CDC Yellow Book: Yellow Fever
WHO classifies 27 African countries and 13 Latin American countries as high-risk for yellow fever outbreaks. It estimates 67,000 to 173,000 severe yellow fever infections each year in Africa and the Americas, with 31,000 to 82,000 deaths annually in those regions. As of 2024, routine infant yellow fever immunization had been introduced in 38 of 40 countries and territories at risk in Africa and the Americas. These are regional estimates and program-coverage figures, not an individual traveler’s probability of infection. WHO: Yellow Fever Fact Sheet and WHO immunization coverage
Polio remains relevant to international travel because importation can occur across borders. WHO says all countries remain at risk of polio importation while poliovirus transmission persists in endemic countries. Worldwide, 84% of infants received three doses of polio vaccine in 2024. The coverage figure describes infants globally; the importation statement describes country-level risk while transmission continues elsewhere. WHO immunization coverage
Cruise ship and travel injuries
Cruise ship medical-center visits show a different pattern from destination-based infections. Respiratory illnesses account for 30% to 40% of visits, slip, trip, and fall injuries for 12% to 18%, gastrointestinal illnesses for about 10%, and seasickness for about 10%. About 95% of acute cruise ship illnesses or injuries are treated onboard. Cardiovascular reasons account for about 3% of medical-center visits, but about 80% of onboard cruise ship deaths are due to cardiovascular events. CDC Yellow Book: Cruise Ship Travel
The CDC also reported that gastrointestinal illness rates on voyages lasting 3 to 21 days fell from 32.5 to 16.9 cases per 100,000 travel days between 2006 and 2019. This is a rate over travel days, rather than a percentage of all passengers, so it should not be compared directly with the percentage breakdown of medical-center visits. CDC Yellow Book: Cruise Ship Travel
Injury risk extends beyond ships. More than 1,500 U.S. citizens died from non-natural causes in foreign countries during 2019 to 2021. Motor vehicle crashes accounted for 26% of those non-natural deaths. The figures cover U.S. citizens abroad and are not a mortality rate for all international travelers. CDC Yellow Book: Injury and Death During Travel
Rabies and Japanese encephalitis
Rabies exposure is uncommon in absolute terms but time-sensitive. Traveler rabies exposure incidence has been estimated at 0.4% per month of stay. Other estimates place exposure rates at 16 to 200 exposures per 100,000 travelers, and most exposures occur within the first 2 weeks of travel. Reported rabies deaths in travelers average about two per year worldwide. CDC Yellow Book: Zoonotic Exposures and CDC Yellow Book: Rabies
Japanese encephalitis causes an estimated 100,000 clinical cases every year. Fewer than 1% of people infected with the virus develop neurologic disease, but the case-fatality rate among encephalitis patients is approximately 20% to 30%. Among survivors, 30% to 50% have serious neurologic, cognitive, or psychiatric sequelae. Transmission risk exists in 24 countries in the WHO South-East Asia and Western Pacific regions, encompassing more than 3 billion people at risk. WHO: Japanese Encephalitis and CDC Yellow Book: Japanese Encephalitis
Altitude illness and oxygen exposure
High-altitude travel changes oxygen availability even without an infection. At about 3,050 meters, inspired oxygen pressure is only 69% of the sea-level value. Acute exposure at that altitude can lower arterial oxygen saturation to 88% to 91%. Any unacclimatized traveler sleeping at 2,450 meters or higher is at risk for altitude illness, and travelers moving to a higher sleeping altitude face risk when the altitude gain is 600 to 900 meters.
The reported frequency varies with ascent conditions. In some rapid-ascent situations, altitude illness rates approach 50%. On standard acclimatization schedules, prevalence can approach 30% at higher elevations. These are context-dependent rates, not a universal percentage for every mountain destination or itinerary. CDC Yellow Book: High-Altitude Travel and Altitude Illness