The swine flu is the common name for the novel strain of influenza A (H1N1) first identified by the U.S. Centers for Disease Control and Prevention (CDC) in April 2009. Compared to other strains of flu, swine flu has predominantly affected younger people, with relatively few cases and deaths reported in people over 65. For people infected with the swine flu, the effects are generally symptoms similar to seasonal flu.
Constitutional Symptoms
Constitutional symptoms of swine flu reflect the immune system's response to the virus. According to a 2009 report in the New England Journal of Medicine, the single most common symptom of swine flu was fever over 101.3 degrees F, reported in 94 percent of laboratory-confirmed cases. However, as the CDC notes, the absence of fever does not necessarily rule out swine flu as the diagnosis. Other constitutional symptoms of swine flu include headaches, body aches, chills and fatigue. In some cases, these symptoms--especially headaches and body aches--may appear before fever.
Respiratory Symptoms
Swine flu, like seasonal flu, is primarily a respiratory infection. After fever, the second most common symptom of swine flu, according to the New England Journal of Medicine, is a cough. The cough associated with swine flu is characteristically dry or "non-productive." Cough that produces green or yellow sputum or copious amounts of clear sputum suggests something other than swine flu. Other respiratory symptoms of swine flu, as described by a 2009 study in the Journal of Clinical Microbiology and Infections, include sore throat (70 percent), runny nose (64 percent) and nasal congestion (56 percent). These symptoms characteristically start a few days after cough and constitutional symptoms.
Gastrointestinal Symptoms
According to the Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team, approximately 38 percent of outpatients with swine flu reported vomiting, diarrhea or both. Vomiting and diarrhea were equally prevalent, each reported by about 25 percent of people. Twelve percent of people had both. In a later study in the Journal of Clinical Microbiology and Infections, diarrhea was slightly more prevalent--31.4 percent compared to 15.1 percent for vomiting. Vomiting tended to resolve more quickly--in two and a half days compared to four days for diarrhea.
Hospitalizations and Deaths
Like seasonal flu, swine flu produces a spectrum of disease ranging from mild, self-limited illness to life-threatening and fatal pneumonia. One distinguishing feature of the swine flu compared to other kinds of flu is the age group it has affected. While 60 percent of hospitalizations and 90 percent of deaths from seasonal flu occur in people over 65, the CDC says that it is people younger than 25 who have been hardest hit by swine flu. In fact, according to the CDC, there have been relatively few swine flu cases and deaths reported in people 65 years and older. One reason for the disparity may be that one-third of people over 60 appear to have antibodies against the virus, while virtually no younger people do.
References
- CDC: 2009 H1N1 Flu ("Swine Flu") and You
- 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); CS Lee and JH Lee; Nov. 13, 2009
