This study is addressed to patients suffering from an acute febrile upper respiratory tract infection suspected to be of viral origin. The purpose of this study is to determine the antipyretic efficacy (reduction of fever by lowering the body temperature from a raised state) of Aspirin in doses of 500 and 1000 mg (study medication) compared to the one of Paracetamol in doses of 500 and 1000 mg (comparator medication) as well as the one of Placebo (comparator medication without an active substance). Despite of its common use for fever treatment, the scientific data in adults which support the antipyretic efficacy of Aspirin are sparse. Therefore, the purpose of this study is to collect such data.