The flu starts suddenly-so suddenly that many people are able to pinpoint the exact time when they became sick, according to Dr. Raphael Dolin in "Harrison's Principles of Internal Medicine." But the beginning symptoms of the flu are different from symptoms that develop later. Knowing the natural history of symptoms helps rule out other kinds of infections and lets someone who's coming down with the flu know what to expect.
Systemic Symptoms
A 2009 study in the Journal of Clinical Microbiology and Infections found that fever, headache and muscle pain were among the presenting symptoms of flu for almost all patients. The study authors defined fever as temperature greater than 100.3 degrees F. But the Centers for Disease Control defines it more loosely, including a subjective feeling of feverishness or chills. Muscle pain is usually felt in the lower back and legs, according to "Harrison's Principles of Internal Medicine."
Respiratory Symptoms
The same study in the Journal of Clinical Microbiology and Infections also found that cough was among the beginning symptoms of flu. Other respiratory symptoms such as sore throat, runny nose and nasal congestion usually developed one to three days later. Breathing problems, reported by up to 22 percent of patients, may present early in the course of the flu for people with certain kinds of lung disease such as asthma, but more commonly develop later.
Altered Mental Status
For some people, especially the elderly and young children, a period of unusual agitation or mental confusion precedes the development of other symptoms. But this is not a specific sign of infection due to flu. Mental status changes typically begin five to seven days before the onset of other symptoms of a variety of illnesses, including urinary tract infection, respiratory tract infection and flu, according to a 2006 study published in the Journal of the American Geriatric Society,
References
- Influenza (Chapter); R. Dolin; In: "Harrison's Principles of Internal Medicine, 17th edition;" A.S. Fauci, E. Braunwald, D.L. Kasper, S.L. Hauser, D.L. Longer, J.L. Jameson and J. Loscalzo (Eds.); 2008
- "Clinical Microbiology and Infections;" Dynamics of Clinical Symptoms in a Case with Pandemic Influenza A (H1N1); C.S. Lee and J.H. Lee; Nov. 13 2009
- "Journal of the American Geriatric Society"; Agitated behavior as a prodromal symptom of influenza; D.L. Mentes and J.C. Woods; Dec.
