Dengue Fever: This is a common cause of fever, thrombocytopenia, and rash, particularly in tropical and subtropical regions. The combination of these symptoms, especially during outbreaks or in endemic areas, makes dengue fever a leading consideration.

Chikungunya: Similar to dengue fever, chikungunya virus infection can cause fever, thrombocytopenia, and a characteristic rash. It's also prevalent in similar geographic regions and should be considered, especially during outbreaks.
Zika Virus Infection: While often associated with congenital abnormalities, Zika virus infection can also present with fever, thrombocytopenia, and a maculopapular rash, making it a plausible diagnosis in endemic areas.
Rocky Mountain Spotted Fever (RMSF): This tick-borne illness can cause fever, thrombocytopenia, and a characteristic rash. It's an important consideration in individuals who have been exposed to ticks, particularly in endemic areas of the United States.

Meningococcemia: This condition, caused by Neisseria meningitidis, can present with fever, rash, and thrombocytopenia. It's a medical emergency due to its high mortality rate if not promptly treated, making it crucial not to miss this diagnosis.
Thrombotic Thrombocytopenic Purpura (TTP): A rare blood disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, renal failure, and neurological symptoms. The presence of fever and rash could be part of the clinical presentation, and TTP is a condition that requires immediate medical attention.
Hemolytic Uremic Syndrome (HUS): Similar to TTP, HUS is characterized by thrombocytopenia, microangiopathic hemolytic anemia, and renal failure. While less commonly associated with rash, the severity of the condition necessitates its consideration to avoid missing a potentially fatal diagnosis.

Ehrlichiosis/Anaplasmosis: These are tick-borne diseases that can cause fever, thrombocytopenia, and sometimes rash. They are less common but should be considered in individuals with a history of tick exposure.
Relapsing Fever: Caused by Borrelia species, this condition can present with recurring episodes of fever, thrombocytopenia, and rash. It's rare and typically associated with exposure to infected ticks or lice.
Viral Hemorrhagic Fevers (VHFs): A group of diseases caused by viruses such as Ebola, Marburg, Lassa, and others. They can cause fever, thrombocytopenia, and rash, among other symptoms. VHFs are rare but highly dangerous and should be considered in individuals with a relevant travel or exposure history.