Chills: Causes, Symptoms, and Associated Conditions

What Are Chills?

Chills are a subjective sensation of coldness accompanied by involuntary shivering (rapid muscle contractions) to generate heat. They often precede or accompany fever but can occur independently.

Common Associated Symptoms

• Fever (often >38.5°C / 101.3°F)
• Headache
• Myalgia (muscle aches)
• Fatigue, weakness
• Nausea, vomiting
• Diarrhea

Major Causes

Infectious

• Viral: Influenza, COVID-19, common cold, mononucleosis, dengue.
• Bacterial: Pneumonia, sepsis, meningitis, UTI/pyelonephritis, endocarditis, cellulitis.
• Fungal: Histoplasmosis, coccidioidomycosis, blastomycosis.
• Parasitic: Malaria (cyclic chills/rigors), toxoplasmosis, babesiosis.

Non-Infectious

• Drug reactions: Chemotherapy, amphotericin B, interferons, antibiotic infusion reactions (e.g., vancomycin "red man syndrome"), immunotherapy.
• Endocrine/Metabolic: Hypoglycemia, thyroid storm, adrenal crisis (Addison's), pheochromocytoma.
• Autoimmune/Inflammatory: Rheumatoid arthritis, SLE, vasculitis, gout flare.
• Malignancy: Lymphoma, leukemia, solid tumors (paraneoplastic).
• Transfusion reactions: Febrile non-hemolytic, hemolytic.
• Environmental: Hypothermia, heat stroke (paradoxical chills).

When to Seek Medical Care

• Chills with high fever (>39.5°C / 103°F) or fever lasting >48 hours.
• Rigors (violent, uncontrollable shaking) suggesting bacteremia/sepsis.
• Altered mental status, hypotension, tachycardia, dyspnea.
• Immunocompromised state (chemotherapy, HIV, steroids, transplant).
• Recent travel to endemic areas (malaria, dengue, etc.).

Diagnosis involves history, physical exam, and targeted labs (CBC, blood cultures, lactate, malaria smear, imaging). Treatment targets the underlying cause.