Differential diagnosis of fever

1. Infectious causes

• Viral: influenza, COVID-19, dengue, EBV, hepatitis, HIV seroconversion
• Bacterial: pneumonia, urinary tract infection/pyelonephritis, cellulitis, gastroenteritis, meningitis, tuberculosis
• Localized or occult infection: abscess, infective endocarditis, osteomyelitis, sinusitis, dental infection
• In hospitalized patients: catheter/line infection, surgical-site infection, C. difficile infection, hospital-acquired pneumonia

• Recent travel: malaria, enteric fever, dengue, rickettsial infection
• Animal/tick exposure: brucellosis, leptospirosis, Lyme disease, rickettsioses
• Immunocompromise: opportunistic infections, disseminated fungal disease, TB

2. Inflammatory and autoimmune causes

• Systemic lupus erythematosus
• Rheumatoid arthritis and adult-onset Still disease
• Vasculitis, including giant-cell arteritis
• Polymyalgia rheumatica
• Sarcoidosis
• Inflammatory bowel disease
• Crystal arthritis, especially acute gout

3. Malignancy

• Lymphoma and leukemia
• Renal-cell carcinoma
• Hepatocellular carcinoma
• Advanced or metastatic solid tumors

4. Drug-related and iatrogenic causes

• Drug fever, commonly with antimicrobials, anticonvulsants, allopurinol and some other agents
• Transfusion reaction
• Vaccination-related fever
• Withdrawal syndromes
• Postoperative inflammatory response

5. Thrombotic, tissue injury, and endocrine causes

• Deep-vein thrombosis or pulmonary embolism
• Myocardial infarction, tissue infarction, hematoma
• Pancreatitis
• Thyroiditis or thyrotoxicosis
• Adrenal crisis

6. Hyperthermia syndromes and other causes

• Heat stroke
• Serotonin syndrome
• Neuroleptic malignant syndrome
• Malignant hyperthermia
• Central fever after stroke, traumatic brain injury, or hypothalamic injury
• Factitious fever

Practical clinical approach

• Duration and pattern, rigors, weight loss, rash, joint pain
• Respiratory, urinary, gastrointestinal, neurologic, and focal symptoms
• Medication changes and recent antibiotics
• Travel, sick contacts, occupation, animals/ticks, sexual history
• Surgery, indwelling lines/catheters, injections, immunosuppression

Seek urgent assessment now if fever occurs with

• Confusion, reduced consciousness, severe weakness
• Severe headache, neck stiffness, or a petechial/purple rash
• Breathlessness, chest pain, low blood pressure, persistent rapid pulse
• Temperature above 40 C
• Pregnancy, neutropenia, major immunosuppression, or age under 3 months

Fever

• A temperature of 38°C (100.4°F) or higher is commonly called fever.
• Common symptoms: feeling hot or cold, chills, sweating, headache, muscle aches, tiredness, thirst, and reduced appetite.
• The temperature itself is often less important than the cause and the person's overall condition.

Common causes

• Viral infections: cold, influenza, COVID-19, dengue
• Bacterial infections: throat infection, pneumonia, urinary infection, skin infection
• Less commonly: inflammatory/autoimmune disease, medication reaction, blood clot, cancer, or heat-related illness

What to do

• Drink fluids and rest.
• Wear light clothing and avoid excessive blankets once chills settle.
• Treat discomfort rather than chasing a normal number.
• Acetaminophen/paracetamol or ibuprofen may reduce discomfort if safe for you. Avoid ibuprofen if you have certain kidney disease, stomach ulcers/bleeding, are on anticoagulants, or have been advised not to use NSAIDs. Do not give aspirin to children or teenagers with viral illness.

Get urgent medical care now for fever with

• Confusion, fainting, seizure, or severe drowsiness
• Severe headache, stiff neck, or purple/petechial rash
• Difficulty breathing, chest pain, blue lips, severe dehydration
• Temperature above 40°C (104°F)
• Pregnancy, severe immune suppression, chemotherapy, or very young infants
• Fever after significant travel, especially with chills or rash

Typhoid fever

Transmission

Incubation period

Clinical features

• Prolonged, gradually rising then sustained high fever
• Headache, fatigue, malaise, loss of appetite
• Abdominal pain or distension
• Constipation or diarrhea
• Dry cough early in illness
• Nausea
• Enlarged liver and spleen
• Relative bradycardia may occur
• Faint salmon-pink rose spots on the trunk in some patients
• Leukopenia may be present

Diagnosis

• Blood culture is the main initial confirmatory test, ideally taken before antibiotics.
• Bone-marrow culture is more sensitive but is not routinely needed.
• Stool or urine cultures may help, especially later in illness or for carrier detection.
• CBC, liver tests, and other tests support assessment but do not confirm diagnosis.
• Widal and many rapid antibody tests are not reliable enough to replace cultures.

Treatment

• Oral or IV fluids
• Nutrition
• Antipyretics for discomfort
• Monitoring for dehydration, bleeding, severe abdominal pain, confusion, or shock

Prevention

• Safe drinking water, sanitation, handwashing, and well-cooked food
• Avoid unsafe ice, raw salads, unpasteurized foods, and street food in high-risk settings
• Typhoid vaccination for people living in or travelling to risk areas. WHO prefers typhoid conjugate vaccine (TCV) in many settings; it can be given from 6 months of age and has longer-lasting protection than older vaccines. The WHO vaccine guidance emphasizes that vaccination complements, not replaces, sanitation and safe water.

Seek urgent care