Viral Hepatitis: The combination of acute elevated liver function tests, cough, fever, nausea, and vomiting in a healthy 22-year-old male suggests a viral etiology. Viral hepatitis (such as hepatitis A, B, or C) can present with these symptoms and significantly elevated liver enzymes.

Influenza or Other Viral Infections: Influenza and other viral infections can cause elevated liver enzymes, especially in the context of a systemic infection with symptoms like cough, fever, and gastrointestinal upset.
Medication-Induced Liver Injury: Although not specified, the use of over-the-counter medications for cough and fever (like acetaminophen) could lead to liver injury, especially if taken in excess.
Alcoholic Liver Disease: While less likely in a healthy 22-year-old without a specified history of alcohol use, acute alcoholic hepatitis could present with elevated liver enzymes and systemic symptoms.

Acetaminophen Overdose: This is a critical diagnosis to consider due to its potential for severe liver damage and the availability of antidotal therapy (N-acetylcysteine). Even if the patient does not admit to an overdose, the possibility of unintentional excessive intake for fever and pain management should be considered.
Budd-Chiari Syndrome: Although rare and less likely given the normal CT evaluation, Budd-Chiari syndrome (hepatic vein thrombosis) can present with acute liver dysfunction and should be considered, especially if there are risk factors for thrombosis.

Autoimmune Hepatitis: This condition can present acutely and would be suggested by very high liver enzymes and possibly autoimmune markers, although it is less common in young males without other autoimmune diseases.
Wilson's Disease: An inherited disorder of copper metabolism that can cause acute liver failure, although it would be unusual for it to first present in adulthood without prior symptoms.
Ischemic Hepatitis (Shock Liver): Could occur in the setting of severe systemic infection leading to hypoperfusion of the liver, but would typically be accompanied by signs of shock or severe hypotension.
Toxic Liver Injury from Other Substances: Exposure to certain toxins or drugs (e.g., mushrooms, certain herbal supplements) could cause acute liver injury, and a thorough history of exposure is necessary to consider these diagnoses.