Breast milk or formula intolerance: This could lead to a transient ketotic state due to an imbalance in nutrient absorption, especially if the infant is transitioning between different types of milk or formulas.

Gastroenteritis: Although the infant has normal vitals and activity, a mild gastrointestinal infection could cause transient ketosis due to dehydration and altered nutrient absorption.
Teething: Teething can sometimes cause changes in feeding patterns or minor infections that might lead to a transient ketotic state.
Viral infections: Mild viral infections, even without significant symptoms, can affect metabolism and lead to ketosis.

Diabetic Ketoacidosis (DKA): Although glucose levels are normal, it's crucial to consider DKA, especially if there's any possibility of undiagnosed diabetes. DKA can present with normal glucose levels in the early stages or if the child has been receiving insulin.
Inborn Errors of Metabolism: Conditions like maple syrup urine disease or fatty acid oxidation disorders can present with ketosis and may not always have other overt symptoms initially.
Adrenal Insufficiency: This condition can cause hypoglycemia and ketosis, although it might not always present with the typical signs of adrenal crisis.

Ketogenic diet effect: If the infant has been started on a ketogenic diet for any reason (e.g., epilepsy), this could lead to ketotic breath.
Idiopathic ketotic hypoglycemia: A rare condition that can cause episodes of hypoglycemia and ketosis, often in the context of fasting or when the child is not feeling well.
Organic acidemias: A group of rare genetic disorders that affect the body's ability to break down amino acids and fatty acids, potentially leading to episodes of ketosis.