Travel-related infections vary greatly by destination, season, duration, and exposure. Travelers’ diarrhea can affect 30%–70% of people on a two-week trip, while Japanese encephalitis among visitors to Asia is estimated below 1 case per million travelers. The figures below distinguish global disease burden, travel-associated cases, historical observations, and modeled or clinical estimates.
Contents
- Travelers’ diarrhea
- Dengue and chikungunya
- Malaria and imported infection
- Food- and water-borne infections
- Yellow fever
- Japanese encephalitis and rabies
Travelers’ diarrhea: attack rates, pathogens, and duration
Travelers’ diarrhea is one of the most frequent health problems associated with international travel. The CDC’s 2026 Yellow Book summarizes attack-rate estimates of 30%–70% during a two-week trip, with variation by destination and season. These are estimates summarized from prior studies, rather than a single global surveillance count. Travelers’ Diarrhea | CDC Yellow Book™
The CDC estimates that bacteria account for 75%–90% of cases. Intestinal viruses account for at least 10%–25% of illnesses, while protozoal pathogens account for approximately 10% of diagnoses, especially among longer-term travelers. These pathogen categories can overlap in broad estimates, so their percentages should not be added as a precise total. Travelers’ Diarrhea | CDC Yellow Book™
Duration also differs by cause:
| Illness category | Reported or estimated duration |
|---|---|
| Untreated bacterial travelers’ diarrhea | Usually 3–7 days |
| Viral travelers’ diarrhea | Generally 2–3 days |
| Protozoal diarrhea | More than 14 days; sometimes months without treatment |
The CDC notes that expatriates living in Kathmandu, Nepal, averaged 3.2 travelers’ diarrhea episodes per person during their first year. The study period is not specified in the CDC summary, so the figure should be read as a location-specific observation rather than a current worldwide rate. Older controlled studies found that prophylactic antibiotics reduced attack rates by 90%; this is a legacy finding, and the summary does not specify the studies’ dates. Travelers’ Diarrhea | CDC Yellow Book™
Persistent post-travel diarrhea can be particularly severe. A 2025 CDC clinical description records 10–20 explosive, watery stools per day in severe cases. Post-Travel Diarrhea | CDC Yellow Book™
The duration estimates also help separate short-lived illness from symptoms that merit a post-travel evaluation. A two- or three-day viral illness sits at one end of the range, whereas protozoal illness lasting beyond 14 days sits at the other. The Kathmandu observation adds a different measure: repeated episodes across a year rather than the duration of one episode. Attack rate, episode frequency, pathogen category, and persistence therefore describe different dimensions of travel-related infection and should not be treated as interchangeable statistics.
Mosquito-borne infections: dengue and chikungunya
Dengue illustrates the difference between a modeled global estimate and reported surveillance totals. A model cited by the World Health Organization estimates 390 million dengue virus infections worldwide each year, including 96 million clinically apparent cases. WHO also states that dengue is endemic in more than 100 countries. Dengue and severe dengue | World Health Organization
WHO received reports of more than 14.6 million dengue cases worldwide in 2024, along with more than 12,000 dengue-related deaths. More than 13 million of those reported cases came from the Region of the Americas. Three European countries reported 308 cases, while Mayotte and Réunion reported 1,291 cases and four deaths. Reported totals and modeled infection estimates measure different things and should not be compared as though they were the same count. Dengue and severe dengue | World Health Organization
Travel-associated dengue has also been tracked in the United States. During 2010–2021, the United States reported 7,528 travel-related cases; 3,135 patients required hospitalization and 19 people died. More than 1,400 travel-associated cases were reported in each of 2022, 2023, and 2024. Dengue | CDC Yellow Book™
Chikungunya outbreaks can affect up to 75% of the population where the virus is circulating, according to the CDC’s 2026 Yellow Book estimate. The United States reported 612 chikungunya cases among travelers during 2018–2023. Chikungunya | CDC Yellow Book™
Malaria burden and imported infection
The WHO estimated 263 million malaria cases and 597,000 malaria deaths worldwide in 2023. Those figures describe global malaria, not only infections in travelers. World malaria report 2024 | World Health Organization
In the United States, almost all of the approximately 2,000 malaria cases occurring annually are imported, according to the CDC’s 2026 Yellow Book. Four states reported 10 locally acquired mosquito-transmitted cases in 2023. The distinction matters: U.S. travel-related malaria statistics largely represent infections acquired abroad and diagnosed after return.
CDC-reported U.S. and territorial cases changed sharply between the following years:
| Reporting year | Malaria cases reported to CDC |
|---|---|
| 2019 | 2,048 |
| 2020 | 602 |
Among U.S. cases in 2019 with a known acquisition country, 93% were acquired in Africa and 4% in Asia. Among U.S. civilians with malaria who reported a travel reason, 76% were visiting friends and relatives. The 2019 figures are historical data summarized in the 2026 edition and do not represent a current annual distribution. Malaria | CDC Yellow Book™
Food- and water-borne infections linked to travel
Typhoid and paratyphoid remain substantial global infections and important travel-associated diagnoses in the United States. The CDC estimates 9.2 million typhoid fever cases and 3.8 million paratyphoid fever cases worldwide each year. Together, the diseases cause an estimated 133,000 deaths annually. Typhoid and Paratyphoid Fever | CDC Yellow Book™
Approximately 85% of U.S. typhoid cases occur among international travelers, compared with approximately 80% of U.S. paratyphoid cases. More than 70% of U.S. travel-associated typhoid and paratyphoid cases occur in travelers returning from South Asia. These are estimates summarized in the CDC’s 2026 edition, not a year-specific U.S. case table.
Among hospitalized typhoid patients, serious complications occur in an estimated 10%–15%. The case-fatality ratio for patients receiving prompt medical care is usually below 1%. Typhoid and Paratyphoid Fever | CDC Yellow Book™
Hepatitis E adds another food- and water-borne risk. WHO estimates that 20 million people are infected globally each year, including an estimated 3.3 million symptomatic infections. Approximately 4,431 people died from hepatitis E in 2023, and nearly 50% of outbreaks occur in camp settings such as refugee or internally displaced-person camps. Hepatitis E | World Health Organization
Yellow fever: risk and severity
Historical travel-associated yellow fever data show how a relatively small number of cases can have severe outcomes. During 1970–2015, 11 cases were reported in people from the United States and Europe who traveled to West Africa or South America. Eight died, a 73% mortality proportion. Only one traveler had documented vaccination, and that traveler survived. Yellow Fever | CDC Yellow Book™
More than 37 travel-associated yellow fever cases were reported in unvaccinated travelers during 2016–2018. For an unvaccinated traveler spending two weeks in endemic West Africa, the estimated risk was 50 illnesses per 100,000 travelers and 10 deaths per 100,000. For the same two-week duration in endemic South America, the estimated risks were 5 illnesses per 100,000 and 1 death per 100,000. These are itinerary-specific estimates, not predictions for every traveler. Yellow Fever | CDC Yellow Book™
Japanese encephalitis and rabies
Japanese encephalitis is uncommon among travelers from non-endemic countries, but cases have been documented. Ninety cases among travelers or expatriates from non-endemic countries were reported during 1973–2022. The estimated incidence among non-endemic-country travelers to Asia is below 1 case per 1 million travelers. Japanese Encephalitis | CDC Yellow Book™
Rabies presents a different pattern: exposure is more common than confirmed travel-related death. Worldwide, rabies causes more than 10 million potential human exposures and more than 10,000 deaths each year. The estimated exposure rate among travelers ranges from 16 to 200 exposures per 100,000 travelers, while reported deaths among travelers average about two per year worldwide. Rabies | CDC Yellow Book™
Together, these figures show why travel-health decisions depend on both probability and consequence. Common gastrointestinal illness contributes much of the routine burden, while imported malaria, severe dengue, yellow fever, and rabies exposure can require prompt clinical attention even when the measured travel-associated count is comparatively small.