Usually occurs in men adults older than 50 yrs. Fever, chills, If you decide the patient has fever and rash, what therapies should you initiate immediately? The differential diagnosis of acute fever and rash in an adult is quite extensive and includes a variety of infectious and non-infectious causes. Infectious disease emergencies and diseases that can have public health implications can present as fever and rash. Chickenpox is an illness that causes a red, itchy rash, fever, headache, sore throat, and body aches. Eczema (infants) Eczema is a common cause of skin rashes in infants, causing redness, bumps, swelling, itchiness, and more. Epiglottitis. Epiglottitis is a rare, life-threatening illness that keeps air from getting to the lungs.