Headache, Fever, Chills, and Chest Discomfort: Differential Diagnosis

This symptom cluster suggests acute infectious or inflammatory processes. Key considerations:

Condition	Key Features
Influenza	Abrupt onset, high fever, myalgia, headache, cough, fatigue; chest tightness possible. Seasonal.
COVID-19	Fever, cough, dyspnea, anosmia/ageusia, myalgia, headache; GI symptoms common. Test to confirm.
Pneumonia	Fever, productive cough, pleuritic chest pain, dyspnea, crackles on exam. CXR confirms.
Acute bronchitis	Cough (dry→productive), low-grade fever, chest tightness/wheeze; viral >90%.
Sinusitis	Facial pain/pressure, purulent discharge, headache, fever; chest symptoms less prominent.
Myocarditis/pericarditis	Post-viral; chest pain (positional), dyspnea, elevated troponin/CRP, ECG changes.
Sepsis	Fever, tachycardia, hypotension, altered mental status; qSOFA ≥2.

Red flags: Dyspnea at rest, hypotension, confusion, hemoptysis, syncope, chest pain radiating to arm/jaw. Seek emergency care.

Diagnosis: history, exam, vital signs, pulse ox, CXR, CBC, CRP, procalcitonin, respiratory viral panel, troponin, ECG, COVID/flu testing.