<s>[INST] What causes ear infections? [/INST] Middle ear infections, which are the most common ear infections, are caused by a bacterium or virus that infects fluid that builds up in the middle ear. Ear infections are often a direct result of a common cold, allergy or other upper respiratory illness. Source: MAYO CLINIC HEALTH SYSTEM. Link: https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/questions-about-earaches-and-ear-infections. Field: Otolaryngology. Disease: Ear Infection </s>