Definition of Tropical Fever
"Tropical fever" is not a single disease entity but rather a clinical syndrome defined as fever (axillary temperature >37.5°C or history of raised temperature, chills, sweating, or headache) occurring in patients who have traveled to or reside in subtropical/tropical regions where the epidemiology of communicable diseases differs from temperate climates. 1
Core Definitional Components
The term encompasses two distinct but overlapping concepts:
Clinical Definition
- Fever presentation: History of raised temperature, feeling hot and cold, chills, sweating, or headache, OR axillary temperature >37.5°C 1
- Geographic context: Exposure to (sub)tropical countries where communicable disease epidemiology differs from temperate climates 1
- Temporal relationship: Symptoms occurring within one year of travel to endemic areas 1
Disease Classification
- "Tropical diseases" specifically refers to infections found more commonly (though not necessarily exclusively) in tropical regions 1
- This distinguishes them from "non-tropical diseases" that occur at similar prevalence globally 1
- The term "tropical diseases" encompasses all diseases occurring principally in the tropics, including communicable diseases caused by bacteria, viruses, parasites, fungi, and arthropod vectors 2
Geographic Scope
Tropical regions are defined as areas lying between and alongside the Tropic of Cancer and Tropic of Capricorn belts, characterized by unique environmental conditions (heat, humidity) and disease epidemiology 2
Clinical Significance in Practice
Most Common Etiologies
When evaluating tropical fever, recognize that:
- Tropical diseases account for only 33% of febrile cases in returning travelers 1
- Malaria is the leading cause (22.2% of all febrile cases, 70.9% of tropical diseases) 1
- Dengue accounts for 5.2% of cases 1
- Enteric fever represents 2.3% 1
- Rickettsioses account for 1.7% 1
- Non-tropical causes (respiratory infections, acute febrile diarrhea) and fever of unknown origin comprise the remaining 67% 1
Syndromic Approach
The Indian Society of Critical Care Medicine recommends classifying tropical fevers into five clinical syndromes for diagnostic and treatment purposes 3:
- Undifferentiated fever
- Fever with rash/thrombocytopenia
- Fever with acute respiratory distress syndrome (ARDS)
- Fever with encephalopathy
- Fever with multi-organ dysfunction syndrome
Important Clinical Caveats
Fever is present in the vast majority of tropical disease presentations: 92% of malaria cases, 78% of dengue, 82% of enteric fever, and 88% of rickettsioses present with fever as the primary complaint 1
Hospitalization and mortality: Among febrile travelers presenting to healthcare, 32% require hospitalization, but mortality remains low at 0.22% 1
Viral infections are the most common overall cause of acute undifferentiated febrile illness in tropical settings (8-11.8% of cases), meaning antibiotics are frequently unnecessary 4