Symptoms of<unk> , with fever and cough the most common symptoms The time between exposure to the virus and development of symptoms, called the incubation period, is 1–4 days, most commonly 1–2 days. Many infections, however, are asymptomatic. The onset of symptoms is sudden, and initial symptoms are predominately non-specific, including fever, chills, headaches, muscle pain or aching, a feeling of discomfort, loss of appetite, lack of energy/fatigue, and confusion. These symptoms are usually accompanied by respiratory symptoms such as a dry cough, sore or dry throat, hoarse voice, and a stuffy or runny nose. Coughing is the most common symptom. Gastrointestinal symptoms may also occur, including nausea, vomiting, diarrhea, and gastroenteritis, especially in children. The standard<unk>  symptoms typically last for 2–8 days. A 2021 study suggests<unk>  can cause long lasting symptoms in a similar way to long COVID. Symptomatic infections are usually mild and limited to the upper respiratory tract, but progression to pneumonia is relatively common. Pneumonia may be caused by the primary viral infection or by a secondary bacterial infection. Primary pneumonia is characterized by rapid progression of fever, cough, labored breathing, and low oxygen levels that cause bluish skin. It is especially common among those who have an underlying cardiovascular disease such as rheumatic heart disease. Secondary pneumonia typically has a period of improvement in symptoms for 1–3 weeks followed by recurrent fever, sputum production, and<unk> id buildup in the lungs, but can also occur just a few days after<unk>  symptoms appear. About a third of primary pneumonia cases are followed by secondary pneumonia, which is most frequently caused by the bacteria Streptococcus pneumoniae and Staphylococcus aureus.
Influenza
Q fever
Swine influenza
Spanish flu
Bird Flu
London flu
Freshers' flu
Polymer fume fever