DDx

Diffuse maculopapular rash

• Viral exanthem: measles, rubella (German measles), erythema infectiosum ("slapped-cheek" disease), exanthem subitum (roseola), primary HIV infection, infectious mononucleosis, dengue
• Other infection: typhoid fever, secondary syphilis, Lyme disease, leptospirosis, rat-bite fever, relapsing fever, ehrlichiosis, epidemic typhus, endemic typhus, scrub typhus, erythema marginatum (rheumatic fever)
• Noninfectious: drug rash (with drug fever or unrelated infection), systemic lupus erythematosus, adult Still’s disease

• Meningococcemia or gonococcemia
• Secondary syphilis
• Rocky Mountain spotted fever
• Erythema multiforme
• Bacterial endocarditis
• Hand, foot, and mouth disease

• Toxic shock syndrome (staphylococcal or streptococcal)
• Scarlet fever
• Kawasaki disease
• Staphylococcal scalded skin syndrome
• Exfoliative erythroderma syndrome (eg, underlying psoriasis, eczema, drug eruption)
• Erythema multiforme major or toxic epidermal necrolysis

• Varicella (chickenpox)
• Staphylococcal scalded skin syndrome
• Erythema multiforme major or toxic epidermal necrolysis
• Hand, foot, and mouth disease
• Rickettsialpox
• Ecthyma gangrenosum (neutropenic, pseudomonal)
• Disseminated Vibrio vulnificus (cirrhosis, seafood or seawater exposure)

• Bacterial endocarditis
• Meningococcemia or gonococcemia
• Rocky Mountain spotted fever
• Purpura fulminans (severe disseminated intravascular coagulation)
• Thrombotic thrombocytopenic purpura
• Other: epidemic typhus, rat-bite fever, enteroviral petechial rash, viral hemorrhagic fever

• Urticarial vasculitis (serum sickness, connective tissue disease, infection, idiopathic)
• Nodules due to disseminated infection (eg, fungal), erythema nodosum, Sweet’s syndrome (acute febrile neutrophilic dermatosis)
• Pustular psoriasis