History and exam
Key diagnostic factors
common
presence of risk factors
Risk factors for yellow fever are recent travel to an endemic area (Central and South America, the Caribbean, Africa), lack of immunisation, mosquito bites (patients often recall a bite from a mosquito), and travel during the rainy and early dry seasons.
fever
Most infections are asymptomatic. Most symptomatic cases present with acute-onset febrile illness, with average temperature 39°C (102°F), lasting 2 to 6 days.[2]
constitutional symptoms
Initial period of infection with abrupt onset of non-specific symptoms such as fever (average temperature 39°C [102°F]), headache, myalgias, dizziness, and malaise lasting 2 to 6 days.[2]
conjunctival injection
Characteristic feature during the period of infection.
uncommon
relative bradycardia (Faget's sign)
Characteristic lack of tachycardia despite high fever during the period of infection, but not present in all patients.
biphasic illness
After initial presentation (period of infection) with acute febrile illness lasting 2 to 6 days, 15% to 25% of patients progress to a more severe form of illness (period of intoxication) with fever, jaundice, abdominal pain, renal failure, and haemorrhagic diathesis after an intervening 24 to 48 hours of defervescence (period of remission).[2]
haemorrhagic diathesis
15% to 25% of patients progress to mild to potentially fatal haemorrhagic fever with petechiae, ecchymoses, or overt bleeding from gums, nose, mucosae, or phlebotomy sites.[2]
signs of renal failure
During the period of intoxication, renal failure, often accompanied by proteinuria and/or hepatic failure (hepatorenal failure), is common.
signs of hepatic failure
In patients with haemorrhagic fever, transaminase levels reflect disease severity. Hepatic failure may ensue and is often accompanied by renal failure (hepatorenal failure).
jaundice
May develop during the period of intoxication.
Other diagnostic factors
uncommon
hypotension
Ominous sign in patients with advanced disease, typically not responsive to fluid replacement and pressor support.
abdominal pain, vomiting, and lethargy
Period of intoxication is characterised by a rebound of symptoms, often accompanied by abdominal pain, vomiting, and lethargy.
Risk factors
strong
residence in, or recent travel to, endemic area
Endemic countries are located within 15°N to 10°S of the Equator and include Africa, the Caribbean, and South and Central America.
Traveller’s risk is determined by various factors including immunisation status, travel location, season, duration of exposure, occupational and recreational activities while travelling, and local rate of virus transmission at the time of travel. Risk of infection is higher during outbreaks.
For a two-week stay, the estimated risks for illness and death in an unvaccinated traveller visiting an endemic area are 50 per 100,000 and 10 per 100,000, respectively in West Africa, and 5 per 100,000 and 1 per 100,000, respectively in South America.[10]
CDC: yellow fever maps Opens in new window
ECDC: yellow fever distribution and areas of risk in Brazil Opens in new window
lack of immunisation
mosquito bite
As mosquitoes are the only known yellow fever vectors, preventing mosquito bites is protective, albeit difficult to implement. Yellow fever is transmitted by Aedes mosquitoes in Africa and Haemagogus mosquitoes in the Americas. Although experimental transmission by the tropical bont tick is possible, it has not been noted in humans.[18]
weak
travel during rainy and early dry seasons
These seasons carry the highest risk of yellow fever transmission due to high mosquito densities.[13]
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