Viral Infection (e.g., influenza, enterovirus, or adenovirus): These infections are common and can cause a petechial rash along with fever, especially in children. The rash is often accompanied by other symptoms such as cough, sore throat, and body aches.

Bacterial Sepsis: Certain bacterial infections, like streptococcal or staphylococcal sepsis, can cause a petechial rash due to the dissemination of bacteria in the bloodstream. Fever is a hallmark of sepsis.
Meningococcemia: This condition, caused by Neisseria meningitidis, can present with a petechial or purpuric rash and fever. It's a serious infection that requires prompt treatment.
Idiopathic Thrombocytopenic Purpura (ITP): Although ITP primarily causes purpura, it can sometimes present with petechiae. Fever may be present, especially if there's an underlying infection contributing to the thrombocytopenia.
Infectious Mononucleosis: Caused by Epstein-Barr virus, this condition can lead to a rash, which may include petechiae, especially if the patient is taking ampicillin.

Meningitis: While not all cases of meningitis present with a rash, some bacterial forms (like meningococcemia) can. Missing this diagnosis can be fatal.
Disseminated Intravascular Coagulation (DIC): This condition can cause petechiae among other symptoms and is often associated with severe infections or other critical illnesses. It requires immediate attention.
Thrombotic Thrombocytopenic Purpura (TTP): A rare disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, renal failure, and neurological symptoms. Petechiae can be part of the presentation.
Severe Dengue Fever: In its severe form, dengue fever can cause a petechial rash, significant bleeding, and low platelet count, along with high fever.

Leptospirosis: A zoonotic infection that can cause a wide range of symptoms, including fever and rash. Petechiae are less common but can occur.
Rickettsial Infections (e.g., Rocky Mountain Spotted Fever): These infections can cause fever, headache, and a characteristic rash, which may include petechiae in some cases.
Henoch-Schönlein Purpura (HSP): Although HSP is more commonly associated with purpura, it can occasionally present with petechiae. It's characterized by the deposition of IgA immune complexes and typically affects children.
Ehlers-Danlos Syndrome with associated bleeding disorder: Certain types of Ehlers-Danlos syndrome can increase the risk of bleeding and may present with easy bruising or petechiae, though this would be more chronic than acute.