Swine flu is the common name for the H1N1 influenza strain first identified in March 2009. According to the World Health Organization, swine flu is a pandemic with cases identified in more than 200 countries and linked to more than 12,000 deaths. In humans, swine flu infection produces systemic, respiratory, gastrointestinal and sometimes neuropsychiatric symptoms.
Systemic
Systemic symptoms reflect the response of the immune system to infection. According to the Centers for Disease Control and Prevention, systemic symptoms of swine flu include fever, headache and muscle pain. Fever above 101.3 degrees F (38 degrees C) is identified in 94 percent of cases. Headache and muscle pain are slightly less common--reported by 60 percent and 43 percent of people, respectively. However, they may precede the onset of fever by one to two days.
Respiratory
According to a 2009 report in the New England Journal of Medicine, cough is the second-most common symptom of swine flu, present in 92 percent of adults. Other common respiratory symptoms of swine flu include, in descending order: sore throat (70 percent), runny nose (64 percent), nasal congestion (56 percent) and mild breathing problems (22 percent). In contrast to cough associated with bacterial infections and allergies, the cough associated with swine flu is dry. Cough is usually the most persistent symptom of swine flu, still present in 10 percent of people more than 10 days later.
Gastrointestinal
Influenza is rarely associated with gastrointestinal symptoms. However, swine flu is somewhat different. According to a report by the Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team, nearly 40 percent of people with swine flu reported diarrhea, vomiting or both. However, in contrast to rotovirus and other more traditional gastrointestinal viral infections, gastrointestinal symptoms of swine flu tend to be short-lived and relatively mild.
Neuropsychiatric
Some people--including the elderly, very young infants and people with certain kinds of medical problems--are unable to mount a fever, even in response to serious infections. In these people, altered mental status may be the first symptom that something is wrong. Examples of altered mental status include confusion, agitation, irritability, hyperactivity, aggressiveness, insomnia or hypersomnia, delusions or hallucinations. According to a 2006 study published in the Journal of the American Geriatric Society, mental status changes paralleled increases in stress hormones measured from saliva and preceded the onset of other symptoms in a variety of illnesses--including urinary tract infection, respiratory tract infection and flu.
References
- New England Journal of Medicine; Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans; Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team; June 18 2009
- Clinical Microbiology and Infections; Dynamics of Clinical Symptoms in a Case with Pandemic Influenza A (H1N1); C.S. Lee and J. H. Lee; November 13 2009
- Journal of the American Geriatric Society; Agitated Behavior as a Prodromal Symptom of Influenza; D.L. Mentes and J.H. Woods; December 2006
