Information on Types of Viral Infections, Types of Viruses, and Symptoms of a with most cases occurring in children under age 15, but older children and adults What is a Viral Infection? · Diagnosing Viral Infections. Viral Syndrome (Adult) A viral illness may cause a number of symptoms. If it settles in your nose, throat, and lungs, it may cause cough, sore throat, congestion, and sometimes headache. If it settles in your stomach and intestinal tract, it may cause vomiting and diarrhea.