Acute Febrile Illness (AFI) refers to a clinical syndrome characterised by the sudden onset of fever (body temperature ≥38°C / 100.4°F) without a clear, immediately obvious cause. AFI is not a specific disease but a symptom complex — a presenting syndrome. It is one of the most common reasons for outpatient and emergency medical consultations in tropical countries like India. The major causes of AFI in India include malaria, dengue fever, typhoid fever, influenza, chikungunya, and leptospirosis.
Acute Febrile Illness (AFI): sudden onset fever ≥38°C without obvious localising cause — a syndrome, not a disease.
Common causes in India: malaria, dengue, typhoid, chikungunya, leptospirosis, scrub typhus, influenza.
Dengue: Aedes mosquito; NS1 antigen test; avoid NSAIDs due to bleeding risk.
Malaria: Plasmodium parasite; intermittent fever with rigors; diagnosed by blood smear or RDT.
Typhoid: Salmonella Typhi; Widal test or blood culture; sustained fever + relative bradycardia.
Scrub typhus: eschar at bite site; treated with doxycycline.
Leptospirosis: from water contaminated with animal urine; conjunctival redness + myalgia.
Management: paracetamol for fever, fluid intake, specific treatment based on confirmed diagnosis.
Acute Febrile Illness (AFI) definition: • Sudden onset of fever: temperature ≥38°C (100.4°F) • Duration: up to 7–14 days (acute) • Without an immediately obvious localising source of infection on initial clinical examination
Key features: • 'Acute' = recent onset (usually within 7 days of presentation) • 'Febrile' = fever present • 'Illness' = systemic symptoms such as malaise, body ache, headache
AFI is a presenting syndrome, not a diagnosis: • The doctor's task is to identify the cause (etiology) of the fever • Many infections present as undifferentiated AFI in early stages
Types of fever patterns (help in diagnosis): • Continuous fever: typhoid, lobar pneumonia • Intermittent fever: malaria (tertian/quartan patterns) • Remittent fever: dengue, bacterial infections • Relapsing fever: Borrelia, brucellosis
Infectious causes (most common):
Malaria • Caused by Plasmodium parasites (P. falciparum, P. vivax most common in India) • Intermittent fever with rigors; diagnosed by peripheral blood smear or RDT (Rapid Diagnostic Test) • Potentially fatal if P. falciparum — treated with artemisinin-based combination therapy
Dengue Fever • Viral — caused by Dengue virus (DENV 1–4), transmitted by Aedes mosquito • High fever, severe headache, retro-orbital pain, joint/muscle pain ('breakbone fever') • Diagnosed by NS1 antigen (early) or IgM/IgG antibodies • Can progress to severe dengue (haemorrhagic fever / shock syndrome)
Typhoid Fever (Enteric Fever) • Bacterial — Salmonella Typhi • Sustained fever, relative bradycardia, coated tongue, splenomegaly • Widal test or blood culture for diagnosis
Influenza • Viral respiratory infection — fever, cough, sore throat, body aches • H1N1 (swine flu) and seasonal influenza important in India
Chikungunya • Viral — transmitted by Aedes mosquito • High fever + severe joint pain (arthralgia); arthritis can persist for weeks/months
Leptospirosis • Bacterial — Leptospira spirochetes; from water/soil contaminated with animal urine • Fever + myalgia + conjunctival redness; Weil's disease = severe form
Scrub Typhus • Rickettsial infection — Orientia tsutsugamushi; transmitted by chigger mite bite • Eschar (dark scab at bite site) is a diagnostic clue; treated with doxycycline
COVID-19 and other viral fever • SARS-CoV-2 and other respiratory viruses can present as AFI
Diagnostic approach to AFI:
History: • Travel history (malaria-endemic area?), mosquito/tick exposure • Contact with animals (leptospirosis, zoonoses) • Vaccination history, food/water source • Duration, pattern, and severity of fever
Examination clues: • Rash: dengue (petechiae), scrub typhus (eschar), typhoid (rose spots) • Splenomegaly: malaria, typhoid • Lymphadenopathy: dengue, scrub typhus • Jaundice: malaria (P. falciparum), leptospirosis • Conjunctival redness: leptospirosis
Basic investigations (initial workup): • Complete Blood Count (CBC): platelets low in dengue; haemolytic anemia in malaria • Peripheral blood smear for malaria parasites • Dengue NS1 antigen/antibody test • Widal test (typhoid) • Urine examination • Liver function tests (LFT)
Management principles: • Antipyretics: paracetamol (acetaminophen) for fever — avoid NSAIDs/aspirin in dengue (bleeding risk) • Oral rehydration — maintain fluid intake • Specific treatment based on confirmed diagnosis (artemisinin for malaria, doxycycline for scrub typhus, antibiotics for typhoid) • Hospital admission if: altered consciousness, severe thrombocytopenia (<20,000/µL in dengue), high parasite density in malaria
Acute Febrile Illness (AFI) is a clinical syndrome defined as the sudden onset of fever (≥38°C / 100.4°F) without an immediately obvious cause on initial examination. It is not a specific disease but a presenting symptom complex. The most common causes in India include malaria, dengue, typhoid fever, chikungunya, leptospirosis, scrub typhus, and influenza.
Common causes of AFI in India include: (1) Malaria — Plasmodium parasites, intermittent fever; (2) Dengue — Dengue virus via Aedes mosquito, petechial rash, thrombocytopenia; (3) Typhoid — Salmonella Typhi, sustained fever; (4) Chikungunya — Aedes mosquito, severe joint pain; (5) Leptospirosis — Leptospira bacteria from contaminated water; (6) Scrub typhus — Orientia tsutsugamushi, eschar; (7) Influenza — respiratory viral infection.
AFI diagnosis involves: history (travel, animal contact, mosquito exposure), physical examination (rash, splenomegaly, eschar, lymphadenopathy), and investigations including CBC (platelet count), peripheral blood smear (malaria), dengue NS1 antigen/antibody test, Widal test (typhoid), urine examination, and liver function tests. The specific investigation depends on clinical suspicion.
Fever in AFI is managed with paracetamol (acetaminophen) as the antipyretic of choice. NSAIDs and aspirin should be avoided — especially in dengue fever due to the risk of bleeding. Oral hydration is important. Specific treatment depends on the confirmed cause: artemisinin-based therapy for malaria, doxycycline for scrub typhus, ciprofloxacin/azithromycin for typhoid, etc.
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