Influenza commonly referred to as "the flu", is a communicable disease caused by an influenza virus. Symptoms can be mild to severe. The most common symptoms include high fever, runny nose, pharyngitis , muscle and joint pain, headache, coughing, and feeling tired. These symptoms typically begin two days after exposure to the virus and most last but every week. The cough, however, may last for quite fortnight . In children, there could also be diarrhea and vomiting, but these aren't common in adults. Diarrhea and vomiting occur more commonly in gastroenteritis, which is an unrelated disease and sometimes inaccurately mentioned as "stomach flu" or the "24-hour flu". Complications of influenza may include viral infection, secondary bacterial pneumonia, sinus infections, and worsening of previous health problems like asthma or coronary failure .
