Post-COVID-19 Encephalopathy: Given the patient's recent exposure to COVID-19 through his wife, who had the virus a week ago, and the presentation of altered mental status without fever, this diagnosis is highly plausible. COVID-19 has been associated with various neurological manifestations, including encephalopathy, even in the absence of severe respiratory symptoms.

Viral Encephalitis: Although the patient is afebrile, viral encephalitis, potentially from a different virus than COVID-19, could still be a consideration. The altered mental status and the fact that the patient is alert and oriented only to person and place (but not time) suggest a possible infectious cause affecting the brain.
Toxic or Metabolic Encephalopathy: This could be due to various substances or metabolic derangements not immediately apparent from the history provided. The stable vitals and lack of significant past medical history do not rule out acute intoxication or a metabolic issue.
Sleep Deprivation or Psychiatric Causes: Given the recent exposure to COVID-19 in the household, stress, lack of sleep, or psychiatric conditions such as anxiety or depression could contribute to altered mental status.

Cerebral Vasculitis or Stroke: Although less likely given the patient's age and presentation, a stroke or cerebral vasculitis (inflammation of the blood vessels in the brain) could present with altered mental status and must be considered due to their potentially devastating consequences if missed.
Meningitis: Despite the absence of fever, meningitis (inflammation of the protective membranes covering the brain and spinal cord) is a critical diagnosis not to miss, as it can present atypically, especially in adults, and has significant morbidity and mortality if not promptly treated.
Subarachnoid Hemorrhage: A sudden onset of altered mental status could be indicative of a subarachnoid hemorrhage, which is a life-threatening condition requiring immediate intervention.

Autoimmune Encephalitis: This is a rare condition characterized by an abnormal immune response targeting the brain, leading to inflammation and altered mental status. It is less likely but should be considered if other diagnoses are ruled out.
Prion Diseases: Extremely rare and typically presenting with rapidly progressive dementia, prion diseases like Creutzfeldt-Jakob disease could be considered in the differential diagnosis of altered mental status, especially if the patient's condition worsens over time.
Mitochondrial Encephalomyopathies: These are a group of rare disorders affecting the mitochondria, which can lead to neurological symptoms, including altered mental status, but are less likely given the acute presentation in this case.