Influenza, more commonly called the flu, is a viral infection that affects up to 25 to 50 million people each year, according to experts at the Flu Facts. Influenza is highly contagious, spread by droplets breathed or coughed into the air. While some people refer to upper respiratory symptoms, such as runny nose, sore throat and sneezing, as the flu, symptoms of the flu are actually much more severe and can last up to a week or more.
Fever and Chills
One of the primary signs of the flu is fever that begins suddenly and lasts three to four days, according to the Flu Facts website. According to the Mayo Clinic, fever is usually over 101 degrees F and may be as high as 103 to 105 degrees F, especially in children. Fever and chills may come on suddenly, according to the Merck Manual. High fever can lead to dehydration, especially if fluid intake is decreased due to lack of appetite. Chills may be followed by a rise in temperature; a drop in temperature is usually accompanied by heavy sweating and a feeling of exhaustion.
People with the flu have generalized achiness, especially in the back, arms and lower legs. Headache is common and may accompany accompanied by photophobia, extreme light sensitivity, according to the Merck Manual. Overwhelming exhaustion is one of the hallmark signs of the flu that occurs early in the disease, according to Flu Facts. Weakness usually accompanies the flu, according to the Mayo Clinic, and can linger up to two weeks after recovery.
Lower Respiratory Symptoms
Lower respiratory symptoms of the flu include cough, dry at first but becoming productive as the disease continues, and chest discomfort. Chest pain and shortness of breath can occur if the flu is complicated by viral or bacterial pneumonia, two frequent complications of the disease, according to the Merck Manual.
Nausea or vomiting, abdominal pain and diarrhea may occur in influenza; these symptoms are more common in infants and young children with the flu, according to the Merck Manual. Loss of appetite is common in both children and adults.