🌡️ Fever = body temperature >38°C (oral/tympanic). It is a protective host response mediated by cytokines (IL-1, IL-6, TNF-α) acting on the hypothalamus. ⚠️ Always distinguish between fever (raised set-point) and hyperthermia (failure of heat dissipation, e.g. heatstroke, NMS, malignant hyperthermia).

📖 General Considerations

🧾 History: onset, duration, rigors, associated symptoms (rash, cough, dysuria, night sweats, weight loss).
🌍 Context: recent travel, contacts, immunisation status, animal exposure.
💊 Drugs: many cause fever (drug fevers, antibiotics, antiepileptics).
🩺 Examination: vitals, hydration, focus on respiratory, abdominal, skin, neuro systems.
🧪 Investigations: FBC, CRP/ESR, U&E, LFTs, cultures, CXR, urine dip, LP if meningitis suspected.

👶 Paediatrics

Fever is very common in children - most due to self-limiting viral infections.
⚠️ Red flags: poor feeding, lethargy, inconsolable irritability, bulging fontanelle, non-blanching rash (meningococcal sepsis), grunting, severe tachypnoea.
Neonates <3 months with fever = sepsis until proven otherwise → admit, septic screen + IV antibiotics.
Febrile convulsions: 6 months–5 years, usually benign, but need to exclude meningitis/encephalitis.
Approach: Traffic light system (NICE CG160) for risk stratification. Most viral → reassure, antipyretics for comfort. Sepsis suspicion → urgent IV antibiotics (cefotaxime ± amoxicillin depending on age).

❤️ Cardiology

Fever is a red flag in cardiac patients - may unmask or worsen disease.
Infective Endocarditis: fever + new murmur, vascular/immune phenomena (Janeway lesions, Osler’s nodes, Roth spots). Blood cultures before antibiotics, TOE is diagnostic. Management → prolonged IV antibiotics ± surgery.
Myocarditis/Pericarditis: viral prodrome followed by chest pain, arrhythmias, raised troponin, ST changes. Treat with supportive care, avoid NSAIDs in myocarditis.
Rheumatic fever: post-streptococcal fever → migratory arthritis, carditis, chorea, rash. Rare in UK but still exam-relevant.
Fever in post-MI or post-valve surgery → always consider infection of lines, wounds, prosthetic valves.

🧬 Haematology/Oncology

Fever in neutropenic patients (post-chemo, haematological malignancy) = medical emergency. ➡️ Admit, cultures, broad-spectrum IV antibiotics <30 min (“door-to-needle”).
Haematological causes: lymphoma, leukaemia (B-symptoms = fever, night sweats, weight loss).
Drug-induced fevers: cytotoxics, antibiotics, allopurinol.
Transfusion reactions can present with fever (febrile non-haemolytic vs haemolytic vs sepsis from contaminated unit).

🏥 General Practice

Most fever in UK general practice = viral URTI, gastroenteritis, UTI.
Role of GP:
- Identify red flags → sepsis (NICE Sepsis NG51), meningitis, pneumonia, pyelonephritis.
- Use NEWS2 in adults, traffic light system in children.
- Safety netting: advise parents/patients when to seek urgent help.
Fever without source → common in children, often viral. In adults, think occult UTI, pneumonia, abscess, or cancer.

🦠 Infection & Tropical Medicine

Common UK infections: pneumonia, UTI, pyelonephritis, cellulitis, influenza, COVID-19.
Sepsis: fever (or hypothermia), tachycardia, tachypnoea, hypotension, raised lactate → give IV antibiotics & fluids rapidly.
PUO (Pyrexia of Unknown Origin): fever >38.3°C for ≥3 weeks with no diagnosis after 3 visits → differential includes TB, endocarditis, lymphoma, vasculitis.
Tropical causes: Malaria (always test in returning travellers), typhoid, dengue, leishmaniasis.

🧾 Investigations Overview

Basic: FBC, CRP/ESR, U&E, LFTs, urinalysis.
Microbiology: cultures (blood, urine, sputum, CSF, stool), malaria screen if travel.
Imaging: CXR, abdominal US/CT if abscess suspected.
Specialist: echocardiogram for endocarditis, bone marrow for haematological malignancy.

🛠️ Management Principles

🎯 Treat the cause (antibiotics, antivirals, antifungals, chemo, immunosuppressants, etc.).
🧊 Symptomatic relief: antipyretics (paracetamol, ibuprofen), hydration, rest.
⚠️ Sepsis → IV fluids, oxygen, IV antibiotics within 1 hour (“Sepsis Six”).
🔍 Always review medications (drug fever is often missed).

📌 Exam Pearls

Febrile child <3 months → always admit and investigate for sepsis.
Neutropenic fever = IV antibiotics within 30 min.
Endocarditis → blood cultures before antibiotics.
PUO differentials = “3 I’s” → Infection, Inflammation, Infiltration (malignancy).
Travel + fever = Malaria until proven otherwise.

📖 References

NICE Sepsis NG51
NICE CG160: Fever in under-5s
Oxford Handbook of Clinical Medicine, 11th ed.
BMJ Best Practice: Fever

🌡️ Case 1 - Community-Acquired Pneumonia

A 64-year-old smoker presents with fever, cough productive of rusty sputum, pleuritic chest pain, and shortness of breath. Chest exam reveals bronchial breathing and crackles in the right lower zone. 💡 Pneumonia is a leading infective cause of fever, particularly in older adults. Typical pathogens include Streptococcus pneumoniae. Diagnosis is supported by CXR. Management involves prompt antibiotics, oxygen if hypoxic, and CURB-65 scoring to guide admission.

🌡️ Case 2 - Urinary Tract Infection / Pyelonephritis

A 35-year-old woman presents with fever, dysuria, flank pain, and rigors. Examination shows costovertebral angle tenderness, and urinalysis reveals nitrites and leukocytes. 💡 UTIs are common bacterial causes of fever, especially in women. When infection ascends to the kidneys, pyelonephritis may cause systemic illness and sepsis. Management includes urine culture and empiric antibiotics, escalated if systemic signs are present.

🌡️ Case 3 - Infective Endocarditis

A 52-year-old man with a prosthetic heart valve develops persistent low-grade fever, weight loss, and night sweats. Exam shows a new murmur and splinter haemorrhages. 💡 Endocarditis is a serious cause of prolonged fever, often due to Staphylococcus aureus or Streptococcus viridans. Diagnosis requires blood cultures and echocardiography (Duke criteria). Management involves prolonged IV antibiotics ± surgery.

🌡️ Case 4 - Malaria (Travel-Related Fever)

A 28-year-old backpacker recently returned from Nigeria develops cyclical fever, chills, and headache. He appears pale with mild jaundice. Blood film shows Plasmodium falciparum parasitaemia. 💡 Malaria should always be considered in travellers with fever. Falciparum malaria can be rapidly fatal without prompt recognition and treatment (artemether-lumefantrine or IV artesunate). Urgent diagnosis and isolation of travel history are essential.

🌡️ Case 5 - Lymphoma (Malignancy-Associated Fever)

A 45-year-old man presents with several weeks of intermittent fever, night sweats, and unintentional weight loss. Exam reveals cervical lymphadenopathy and splenomegaly. 💡 Fever may be non-infective, occurring in malignancies such as lymphoma (part of “B symptoms”). It reflects cytokine release from tumour activity. Diagnosis is confirmed by biopsy. Management involves chemotherapy, radiotherapy, or immunotherapy depending on subtype.

🌡️ Case 6 - Viral Upper Respiratory Tract Infection (Child)

A 4-year-old boy presents with a 2-day history of fever, runny nose, mild cough, and sore throat. Examination shows mild pharyngeal erythema but no focal chest signs. 💡 Viral URTIs are the most common cause of fever in children. They are usually self-limiting and rarely require antibiotics. The key skill is careful safety-netting - advising parents on red-flag features such as breathing difficulty, poor fluid intake, or lethargy.

🌡️ Case 7 - Meningococcal Septicaemia (Child)

A 7-year-old girl is brought in with fever, headache, and drowsiness. She has a non-blanching purpuric rash on her legs and neck stiffness. 💡 Meningococcal disease is a life-threatening cause of fever in children and must be recognised early. The combination of fever and non-blanching rash should trigger immediate treatment with IV/IM antibiotics (e.g. ceftriaxone) and urgent hospital admission for supportive care and public health notification.

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Fever - all ages