Metallosis or Metal Hypersensitivity Reaction: This is a possible reaction to the metal components of the hip replacement, which can cause a systemic inflammatory response, including fever, joint erythema, and elevated neutrophils and eosinophils.

Infection (e.g., Prosthetic Joint Infection): Although less common at 1 week post-surgery, infection remains a concern, especially with symptoms like fever and elevated neutrophils.
Acute Crystal Arthropathy (e.g., Gout or Pseudogout): These conditions can cause sudden onset of joint pain, erythema, and swelling, and may be triggered by the stress of surgery.
Serum Sickness-like Reaction: This is an immune-mediated reaction that can occur after surgery, characterized by fever, rash, and arthralgias, which could fit the presentation.

Sepsis: Although the presentation might not be typical, sepsis is a life-threatening condition that requires immediate attention. The presence of fever and elevated neutrophils necessitates ruling out sepsis.
Deep Vein Thrombosis (DVT) or Pulmonary Embolism (PE): These are potential complications post-surgery, especially with recent immobilization. While the symptoms don't directly point to DVT/PE, the recent surgery and potential for thromboembolic events make these diagnoses critical not to miss.
Infectious Endocarditis: Although less likely without a clear source of infection or pre-existing heart condition, the presence of fever and systemic symptoms post-surgery warrants consideration of this potentially deadly diagnosis.

Adult-Onset Still's Disease: A rare autoimmune condition characterized by high fevers, joint pain, and rash, which could fit some aspects of the presentation.
Eosinophilia-Myalgia Syndrome: A rare condition associated with elevated eosinophils and muscle pain, which might be considered given the eosinophilia but is less likely given the context of recent surgery.
Hematologic Malignancy: Certain blood cancers can present with systemic symptoms like fever and joint pain, although this would be an uncommon initial presentation and more investigation would be needed to consider this diagnosis.