The rash with maculopapules and fever in adults.

There is a broad differential diagnosis for the presentation of fever and maculopapular rash in an adult. Although some causative conditions are benign, others are medical emergencies that require prompt diagnosis. We describe various conditions that result in a fever and maculopapular rash in adults. These include infectious processes (meningococcemia, infectious mononucleosis, West Nile virus, zika virus, rubella, primary human immunodeficiency virus, parvovirus B19, ebolavirus), tick-borne illnesses (Rocky Mountain spotted fever, ehrlichiosis), and hypersensitivity reactions (exanthematous drug reactions). We also provide an algorithm to aid in the diagnosis of the patient with fever and maculopapular rash. Such conditions that can occur in adults but are seen predominantly in children are discussed in the article "Rash with maculopapules and fever in children" of this issue.