Symptoms of influenza virus are usually experienced one to four days after infection occurs. During this incubation period the virus replicates in the respiratory tract. Influenza can spread to other persons before symptoms start and up to three to four days after symptoms appear.
Usually the symptoms start very quickly and can include
Sudden onset of chills
Generalized aches and pains (most pronounced in the back and legs)
Fever (usually 38 oC to 39,5 oC /100oF-103oF/ in adults and often even higher in children) lasting from one day to a week
Runny or stuffy nose
Scratchy and sore throat
Fatigue, weakness and sweating
Warm and flushed skin
Loss of appetite
Inflammation of conjunctiva
Flu normally lasts for approximately one week. Nausea, vomiting and diarrhea can sometimes accompany the infection, especially in children, but they are rarely the primary symptoms. Only in very rare cases does the flu cause symptoms in the stomach or the intestines. The so-called "stomach flu" is not influenza, but rather an infection caused by bacteria or other viruses such as adeno- or rotavirus. Influenza has been recently demonstrated as a major cause of pediatric otitis media.