The returning traveller with fever

• Fever after international travel can be a common infection or a rapidly progressing tropical one; the first task is to decide how sick the person is and whether they need isolation.
• Malaria is the most common life-threatening tropical cause and must be excluded in anyone who has been to a malaria-endemic area within the previous 12 months, irrespective of prophylaxis.
• Geography and the time since return narrow the list: dengue, malaria and influenza come early, whereas malaria, hepatitis and leishmaniasis can appear weeks later, and viral haemorrhagic fevers usually declare within 3 weeks.
• A cause is never found in roughly 1 in 4 returned travellers; most of these recover on their own.
• A "viral special pathogen" (Ebola, Lassa, Marburg and similar) is rare in travellers, but a good travel history and prompt isolation save lives when it is possible.

By the end of this page you should be able to:

1. Take a complete travel, exposure and prophylaxis history, and estimate pre-test probability from geography and incubation.
2. Triage a febrile returned traveller, including when to admit and when to isolate.
3. Exclude malaria rapidly with appropriate testing and know when empiric treatment is justified.
4. Recognise and manage the main differentials: dengue, typhoid and paratyphoid fever, rickettsial disease and viral haemorrhagic fever.
5. Choose first-line investigations and interpret the common laboratory patterns (normal or low white cell count, thrombocytopenia, haemorrhage).
6. Know the public-health reporting and containment steps for a suspected viral special pathogen.
7. Adapt the approach when blood smears, artemisinin-based therapy or isolation facilities are limited.

Fever in a traveller recently back from abroad is one of the few clinical problems in which a "common or garden" infection and a life-threatening tropical one sit side by side. As many as 43-79% of travellers to low- and middle-income countries become ill during or after travel.^[1] Most of these illnesses are mild and self-limiting, but some deteriorate quickly, and a traveller can look well at first and then become critically ill within hours.

The stakes are genuinely asymmetric. Missing malaria, typhoid, a rickettsial infection or a viral haemorrhagic fever costs a life; over-investigating every returning backpacker wastes resources and delays discharge. The aim is therefore a staged approach: triage safely, exclude malaria first because it is the commonest life-threatening tropical cause and it is treatable, then use geography and incubation to narrow the remaining list, and keep common infections (pneumonia, urinary infection, diarrhoeal illness) in mind throughout.^[1]

Healthcare professionals should stay informed of current outbreaks in the destination countries their patients visit, and every ill returned traveller needs a thorough medical and travel history. Surveillance data such as the GeoSentinel network show that the frequency of diagnoses varies with the region visited: among febrile returned travellers, dengue is diagnosed most often in travellers returning from Asia, and malaria most often in those returning from Africa.^[1]

This page assumes an adult in the first weeks after return. Malaria, dengue, typhoid and the other major infections in travellers are covered in more depth in their own MedGrasp topics; this page links them as a single pathway. The cross-check with prolonged unexplained fever is covered in the fever of unknown origin topic, and this page overlaps with it only on the first two weeks.

Three points make or break the first hour.

First, take a real travel history, not a tick-box one. Ask for exact destinations at sub-national level (malaria is seasonal and provincial in several countries), dates of departure and return, reason for travel, exposures (mosquitoes, ticks, freshwater, animal contact, food, sexual contact, healthcare abroad), accommodation, prophylaxis and adherence, and whether fellow travellers are ill.^[1] Visiting friends and relatives is a major risk factor: these travellers are at greater risk of malaria, typhoid fever, parasitic infections and tuberculosis, often because they stay longer, travel more remotely, eat local food and do not seek pre-travel advice.^[1]

Second, admission should be easy. Most post-travel illnesses are managed as an outpatient, but the threshold for admitting undifferentiated systemic febrile illness should be low, particularly for older travellers and those with comorbidities, and especially when follow-up cannot be relied upon.^[1]

Third, keep infection control, public health and reportability in mind from the start, because the same first assessment can be both diagnostic and protective.^[1]

Accurate triage protects healthcare workers, other patients and the public, avoids treatment delays and selects the right level of care. Potentially severe, transmissible infections may need enhanced precautions: respirators, face masks, eye protection, gloves, gowns, airborne infection isolation rooms, or high-level isolation units.^[1][4]

High-consequence infectious diseases (HCIDs) are defined in the United Kingdom as acute infectious diseases with a high case-fatality rate, limited prophylaxis or treatment, often difficult to recognise rapidly, able to spread in the community and in healthcare settings, and requiring an enhanced system response.^[5] They split into contact (such as Ebola, Marburg, Lassa, Crimean-Congo haemorrhagic fever) and airborne groups (such as MERS, Nipah, pneumonic plague). In the UK, suspected and confirmed HCID cases need specific infection prevention and control measures in all settings, and the Imported Fever Service provides 24-hour telephone access to expert clinical and microbiological advice.^[5]

For a suspected viral special pathogen the guiding idiom is Identify, Isolate, Inform.^[4]

• Identify: a full travel and exposure history, because none of these viruses is endemic in the destination country.
• Isolate: a private room with a door and private bathroom or covered bedside commode; negative pressure if respiratory symptoms are present; strict precautions maintained until the pathogen is ruled out, which may take several days.^[4]
• Inform: the local public health department first, with CDC consulted for serious considerations; in the UK, the Imported Fever Service.

If a private room is not available, a separate enclosed area with a private bathroom or covered bedside commode is acceptable.^[4] Pathways to the evaluation area should be chosen to reduce exposure to others, and only trained essential personnel should enter the room, with a log of everyone who does.^[4]

Suspected illnesses that should trigger public-health involvement immediately include a viral haemorrhagic fever (especially bruising or unusual bleeding), persistent cough (tuberculosis or pertussis), decreased consciousness (meningococcal meningitis), persistent voluminous diarrhoea (cholera), flaccid paralysis (polio), jaundice (hepatitis A), rapid respiratory rate (COVID-19, influenza, MERS, pneumonic plague), rash (measles, meningococcaemia, monkeypox, viral haemorrhagic fevers) and persistent vomiting (norovirus).^[1]

Geography sets the prior probabilities and incubation sets the time course. Most travel-associated infections have short incubation periods, so most acutely ill travellers present within 1 month of return; a malaria-endemic area visited up to 12 months ago still belongs in the differential.^[1]

The tables below summarise common causes of fever by region and by incubation. They are guides, not laws: sub-national geography, rural versus urban setting and season all matter, and malaria is endemic only in some provinces of otherwise low-risk countries.^[1]

Two time rules capture most of the useful behaviour. Diseases with incubation under 2 weeks (dengue, chikungunya, influenza, travellers' diarrhoea) declare early. Diseases with incubation of 2-6 weeks include viral hepatitis, acute HIV, leishmaniasis, malaria and typhoid. Infections that can surface months or years later include leishmaniasis, malaria (especially P. vivax and P. ovale), schistosomiasis, strongyloidiasis, filariasis and tuberculosis. Viral haemorrhagic fevers almost never exceed 21 days; if symptoms start later, the risk is negligible.^[1]

Investigations should follow from the clinical assessment rather than from a long list of exotic tests. The initial approach is that of any routine clinical evaluation, with a few travel-specific additions.

• Complete physical examination, repeated at least daily if the diagnosis is unclear, because new signs (skin lesions, a tender liver, an eschar) can appear after admission.^[1]
• Malaria testing in everyone with fever and an endemic destination, with a same-day blood smear or rapid test.^[4]
• Full blood count, film and biochemistry; blood cultures (multiple, with prolonged incubation) where typhoid is plausible; arbovirus PCR or serology where available; urinalysis; chest X-ray if indicated.
• Stool culture and microscopy if diarrhoea is prominent, and respiratory testing for influenza and COVID-19 in season.
• The travel history on the request form, so the laboratory can choose the right assays.^[1]
• Targeted tests by exposure: schistosome serology after freshwater exposure, rickettsial serology when there is tick exposure with fever, headache and rash, leptospira testing when there is haemorrhage and jaundice.

A normal or low white cell count supports a rickettsial infection, typhoid or paratyphoid fever, chikungunya, dengue, acute HIV or malaria; rash supports meningococcaemia, rickettsial infection, typhoid, arboviral infection, measles or Zika; haemorrhage (petechiae, purpura, epistaxis, gastrointestinal bleeding) raises leptospirosis, meningococcaemia, rickettsial spotted fever and the viral haemorrhagic fevers; jaundice raises leptospirosis, malaria, hepatitis and yellow fever.^[1]

Two caveats are worth carrying into practice. First, do not overlook common and cosmopolitan infections (diarrhoeal illness, pneumonia, pyelonephritis) in the search for exotic diagnoses; take their usual differentials and expand them using the travel risk factors rather than discarding them.^[1] Second, fever with bleeding collapses to a short list in which the bacterial causes (leptospirosis, meningococcaemia, rickettsial infection) are treatable and must be considered alongside the viral haemorrhagic fevers, even when the latter are the headline concern.^[1]

Where fever persists beyond 3 weeks and remains unexplained after standard work-up, the condition is a fever of unknown origin, and the systematic approach in the MedGrasp fever of unknown origin topic should be followed. Returning-traveller fever is the most common starting point for that longer evaluation.

Malaria is the most common life-threatening tropical disease associated with fever in returned travellers, with roughly 2,000 cases diagnosed each year in the United States. It is the diagnosis that should be ruled out in every febrile returned traveller who has been to an endemic area, and a history of chemoprophylaxis does not exclude it: more than 90% of US residents with travel-associated malaria report not having adhered to a recommended regimen.^[1]

Key epidemiological facts:

• P. falciparum manifests in more than 90% of cases within 30 days of return; P. vivax in about half of cases more than 30 days after return, and it can appear up to 12 months later.^[1]
• Severe malaria (shock, pulmonary oedema, significant bleeding, seizures, impaired consciousness, renal impairment, acidosis, anaemia, high parasitaemia) occurs in roughly 10% of patients, and about 0.3% of people who receive a diagnosis die.^[1]
• P. falciparum can progress to severe illness and death within 24 hours if untreated.^[6]
• Travellers, infants, young children, pregnant people and people with HIV are at higher risk of severe disease.^[6]

Diagnosis and initial management:

• Test with microscopy and (if needed) a rapid test the same day; an immediate blood smear with same-day result is ideal.^[4]
• A negative test does not clear malaria if suspicion is high; repeat the test when clinical suspicion remains, and follow the local protocol for how many films are required to exclude malaria.^[1]
• Patients with malaria can be afebrile at evaluation; a history of fever or chills is the more reliable clue.^[1]
• Thick and thin smears may be inactivated with methanol for safe handling.^[4]
• If testing is delayed and suspicion is substantial, empiric antimalarial therapy may be justified.^[1][4]
• P. falciparum is treated with artemisinin-based combination therapy; P. vivax or P. ovale should receive primaquine to prevent relapse, where the drug is tolerated and the parasite is susceptible.^[6]

Empiric parenteral antimalarial treatment is rarely indicated without confirmed parasitaemia, except in rare circumstances.^[1] Where laboratory testing is unavailable and the pre-test probability is low, treat the fever syndrome and review within 24 hours rather than give a blanket antimalarial.

Pre-travel chemoprophylaxis is started 2-3 weeks before departure and continued for 4 weeks after the last possible exposure.^[6] The MedGrasp malaria topic covers the disease itself, including severity criteria, organ support and the choice of artemisinin-based regimens.

Dengue is the most common cause of febrile illness in travellers returning from Latin America and Asia, and malaria takes that place for Sub-Saharan Africa. It is an arbovirus spread by Aedes mosquitoes that bite in the daytime, so the classic travel risk is urban daytime exposure.^[1][7]

Clinical picture: incubation 4-8 days (range 3-14). Fever, headache, retro-orbital pain and myalgia, often with rash a few days in. Typical laboratory clues are a normal or low white cell count and thrombocytopenia. There is no specific antiviral; management is supportive, with careful fluid balance.^[1][7]

Warning signs of progression to severe dengue include abdominal pain, persistent vomiting, mucosal bleeding, lethargy or restlessness, hepatomegaly and a rising haematocrit with falling platelets; these patients need inpatient care and close fluid monitoring. Because more than one arbovirus may circulate in the same region (chikungunya, Zika, yellow fever), clinical differentiation is often difficult where testing is limited, which is why the WHO 2025 guideline groups these infections together and stresses an integrated approach.^[7]

The WHO 2025 guidelines for clinical management of arboviral diseases note that early detection and access to proper care greatly lower fatality rates of severe dengue, and estimate about 390 million infections a year, of which roughly 96 million manifest clinically; over 5.6 billion people worldwide are at risk of arboviral infection.^[7]

Together these are "enteric fever": a Salmonella enterica (serotypes Typhi and Paratyphi A, B or C) bacteraemia with an insidious onset. About 9.2 million typhoid and 3.8 million paratyphoid cases occur worldwide each year, causing roughly 133,000 deaths; more than 70% of US cases are in returned travellers, and most of those have been to South Asia (mainly Bangladesh, India, Pakistan).^[2]

• Incubation: typhoid 6-30 days, paratyphoid 1-10 days (ranges wider with host factors and dose).^[2]
• Onset is gradual, with fever climbing daily from low-grade to 39-40 degrees C by the third or fourth day, lowest in the morning and peaking in the late afternoon. Headache, malaise, anorexia and abdominal pain are common; rose spots may appear on the trunk. Untreated illness can last a month.^[2]
• Blood culture is positive in about 50% of cases (higher with multiple cultures), and bone marrow culture in about 80%. Serology (Widal) is unreliable.^[2]
• Untreated case-fatality exceeds 10%; with prompt care it is usually under 1%. Serious complications (gastrointestinal haemorrhage, perforation, encephalopathy) occur in 10-15% of hospitalised patients, usually after 2-3 weeks.^[2]
• Treatment: fluoroquinolones remain first choice for susceptible strains, but most isolates from South Asia are now fluoroquinolone-nonsusceptible; empiric therapy must therefore be guided by travel history - azithromycin (plus a carbapenem for severe or Iraq/Pakistan travel) or ceftriaxone with azithromycin for most other origins - with later adjustment based on susceptibility testing.^[2]
• Fever may persist for 3-5 days after starting antibiotics, generally decreasing each day; if fever persists beyond 5 days, reconsider the diagnosis or look for a persistent focus. Relapse occurs in up to 10% of patients within 1-3 weeks of recovery, and 1-4% become chronic carriers.^[2]
• Typhoid vaccine gives 50-80% protection, conjugate vaccines are WHO-prequalified, and no vaccine exists for paratyphoid fever; food and water precautions remain essential.^[2]

Typhoid is a nationally notifiable disease in many countries, and any domestically acquired case triggers a public-health investigation. The MedGrasp typhoid topic covers the disease itself, resistance patterns and vaccination policy.

These are infections caused by obligate intracellular bacteria spread by fleas, lice, mites and ticks. They are the most frequently reported travel-associated tick-borne infections, and African tick bite fever is the most commonly diagnosed rickettsial disease in travellers - and the second most common cause of fever (after malaria) in travellers returning from Sub-Saharan Africa.^[3]

• Incubation is 5-10 days, so symptoms appear during the trip or within 1-2 weeks of return.^[3]
• The classic triad of fever, headache and rash is present variably and is not a reliable diagnostic test. Many patients instead have a non-specific febrile illness with eschar, regional lymphadenopathy or a maculopapular, vesicular or petechial rash. About half of murine typhus cases show a maculopapular rash; scrub typhus produces respiratory symptoms in about two-thirds of patients.^[3]
• Life-threatening forms include Rocky Mountain spotted fever, scrub typhus, Mediterranean spotted fever, murine typhus and epidemic typhus, especially when treatment is delayed; Rocky Mountain spotted fever carries a case-fatality of 20-40% in that situation.^[3]
• Doxycycline is the treatment of choice for all rickettsioses: 100 mg by mouth twice daily for at least 5-7 days, or 2.2 mg/kg twice daily for children under 45 kg. Start it as soon as the disease is suspected - never withhold it pending confirmatory testing - because early treatment saves lives and prevents sequelae.^[3]
• Chloramphenicol is an alternative where tetracyclines are not tolerated or in pregnancy, but with higher case-fatality, particularly in Rocky Mountain spotted fever; azithromycin may be effective for tetracycline-resistant scrub typhus, and adding intravenous azithromycin to doxycycline can speed resolution in severe scrub typhus. Rifampin is an alternative for some pregnant or doxycycline-intolerant patients with Anaplasma or Rickettsia africae infection.^[3]
• Short-course doxycycline has not been shown to cause dental enamel staining in children under 8, so age alone should not delay treatment.^[3]
• Diagnosis is clinical during the acute illness; serology confirms retrospectively on paired samples 2-4 weeks apart, with a four-fold rise being diagnostic. PCR of an eschar is sensitive and species-specific.^[3]
• Antibiotics are not recommended for prophylaxis after a tick bite.^[3]

Scrub typhus, murine (endemic) typhus, Rocky Mountain spotted fever and Mediterranean spotted fever are the names that matter most in travellers, and all share the same treatment: doxycycline, early.

These are rare but devastating in travellers, which is why they structure the triage step rather than being an afterthought. The group includes the filoviruses (Ebola, Marburg), arenaviruses (Lassa, Junin, Machupo and others), nairoviruses (Crimean-Congo haemorrhagic fever) and henipaviruses (Nipah), with yellow fever and dengue also producing haemorrhagic forms. They spread person-to-person, cause severe morbidity or death, and have limited countermeasures.^[4]

Clinical pointers:

• Incubation is short: Ebola and Marburg 2-21 days, Lassa 2-21 days, Crimean-Congo haemorrhagic fever 1-14 days, Nipah 5-14 days, MERS 2-14 days. Incubation rarely exceeds 21 days, and the risk is negligible if symptoms begin later than that.^[1][4]
• Lassa fever is asymptomatic or flu-like in roughly 80% of infections; severe cases resemble Ebola disease. ^[4] Ebola, Marburg, Sudan and related viruses begin with a non-specific flu-like illness, with progression to bleeding, multi-organ failure and dehydration.

Isolation principles for a suspected case:

• Place the patient immediately in a private room with a door and private bathroom or covered bedside commode; consider negative pressure if respiratory symptoms are present. If no private room is available, a separate enclosed area with private bathroom or commode is acceptable. Use portable HEPA filtration if no anteroom exists.^[4]
• Limit entrants to trained essential personnel with designated roles; log everyone; take histories by phone or tablet where the patient is stable; bring all supplies in at once; use disposable equipment.^[4]
• All interactions happen under strict isolation precautions until the pathogen is excluded, which may take several days; precautions are applied uniformly and not adjusted for gradations of risk.^[4]
• First contact is the local public health department, with CDC consultation for serious considerations (770-488-7100).^[4]
• Empiric management centres on fluids and electrolytes, oxygen, glucose control (hypoglycaemia is a known complication of Ebola and severe malaria) and broad-spectrum antimicrobials. If malaria testing is delayed, empiric antimalarial therapy is appropriate, and doxycycline should be started if rickettsial disease is suspected. Influenza and COVID-19 antivirals are safe early options. Ribavirin has been used (off-label in many countries) for Lassa fever and Crimean-Congo haemorrhagic fever; Ebanga and Inmazeb reduce mortality in Ebola disease.^[4]
• Without treatment, Ebola mortality can reach 90%.^[4]
• Reporting and isolation are compulsory under public-health law in most countries. In the UK, HCIDs require specific infection prevention and control measures in all settings and transfer to designated HCID treatment centres once confirmed; the Imported Fever Service gives 24-hour expert clinical and microbiological advice.^[5]

The structure of the assessment changes less than the tools do.

• A transthoracic echocardiogram is the single transformative test for some presentations, but for fever the equivalent is the blood smear: make it as fast and as reliable as possible.^[4]
• Repeat the history and examination daily if the diagnosis remains unclear; time and observation solve cases when technology does not.^[1]
• Where culture is unreliable, rely on syndrome-based empiric therapy with the widest available coverage and the safest drugs.
• Chloramphenicol remains a usable alternative for rickettsial infection where doxycycline is not tolerated, but case-fatality is higher, particularly in Rocky Mountain spotted fever.^[3]
• Typhoid and paratyphoid cases are largely acquired abroad and in low-resource settings; typhoid Vi conjugate vaccines are now WHO-prequalified, but paratyphoid has no vaccine, so food and water precautions remain the only protection.^[2]
• Trust building, clear isolation and early contact with public health authorities matter more, not less, where infrastructure is thin. Reportability does not disappear with distance.

Red flags at any resource level remain the same: altered consciousness, shock, severe respiratory distress, bleeding, severe anaemia and persistent fever beyond a few days without improvement.

• Malaria
• Typhoid and paratyphoid fever
• Dengue
• Rickettsial diseases
• Fever of unknown origin
• Viral haemorrhagic fevers