What element in a child's history is most significant for a tentative diagnosis of Reye syndrome?

The most significant element in a child's history for a tentative diagnosis of Reye syndrome is a recent viral infection. Reye syndrome is a rare but serious condition that typically occurs in children and is associated with the use of aspirin during or after a viral illness. The condition often follows viral infections such as influenza or chickenpox.

Identifying a recent viral infection is crucial because it helps to establish a link between the child's prior health status and the development of Reye syndrome, which is characterized by rapid progressive encephalopathy and liver dysfunction. The association with viral infections underscores the importance of careful history-taking to identify potential risk factors in affected children, especially when aspirin has been administered.

Other elements listed, such as a recent rash, tonsillitis attacks, or recurrent high fevers, do not provide the same level of significance in diagnosing Reye syndrome. These may indicate other medical conditions but lack the direct correlation that recent viral infections have with the syndrome's pathology and risk factors.