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. Apr 25, - What's the difference between a bacterial and viral infection? WebMD explains, and provides information on the causes and treatments for.