U.S. military personnel analyzed an outbreak at the Air Force Academy in July 2009. From that study, they were able to develop a list of the most common symptoms of swine flu. The outbreak is a good model because all of the patients were young, fit and had no underlying medical conditions. Symptoms may vary in other groups of people.
134 cadets tested positive for pandemic flu, H1N1, the swine flu. Not all sick cadets experienced every symptom but the study was able to rank a number by frequency of occurrence.
The first key symptom is a high fever. 94% of the cadets who fell ill had a fever over 100 degrees. Fevers over 103 degrees begin to be dangerous. A spiking fever, rapid onset and rapid increase to a high temperature, is also a sign of danger. Headache and chills may accompany the fever. CDC WebMD Mayo Clinic Among the cadets, 84% suffered a headache and 81% chills.
The common cold will share many of the same symptoms as influenza. The length of the infection may be shorter in most cases with less severe symptoms. Infants and young children are most likely to have a fever, normally low grade meaning under 100.4 degrees.
Influenza, including the swine flu, will produces symptoms in the respiratory systems. Lung congestion, cough and a runny or stuffy nose may be seen. Symptoms that cause trouble breathing, pale or gray skin or pain in the chest and abdomen are serious and require emergency medical care. This have been some clinical suggestions that swine flu may infect deeper in the lungs than seasonal flu, making the respiratory symptoms worse and of more concern. A cough was the second most common symptom for the cadets, at 93%. Just under 50% had a runny nose.
All influenzas produce aches and pains, and fatigue. The swine flu is little different. The aches and the fatigue can be extreme, and last for a week or more. Most of the cases of swine flu seen to date in this pandemic have been characterized as mild. The length of time patients suffer symptoms may be several days less than with another fly strain. Among the cadets, body aches were a symptom for 63% and fatigue was suffered more often, by 86% of the sick cadets.
With the seasonal flu, children may experience vomiting and diarrhea. Adults are unlikely to have these symptoms. With swine flu, it appears that adults are also experiencing gastric symptoms. The combination of fever and gastric symptoms can easily lead to dehydration. Inability to eat or drink for several days requires emergency medical attention. Only seven percent of the cadets suffered vomiting or diarrhea.
There are many illnesses that produce similar symptoms to those produced by an influenza infection. The medical term is "influenza-like illnesses" (ILI). The most distinguishing symptoms of influenza are the length of the illness, a week or more, and a fever. Gastric symptoms in an adult who also has a fever, respiratory symptoms, and extreme fatigue may well mean that the person has swine flu.
One of the unique aspects of the current outbreak of swine flu is the age group most affected. Seasonal influenza is seen most often in those under 4 and over 50. Swine flu is being found almost entirely in people under 50, with about half of the patients under 18. The symptoms of swine flu, when seen in someone under 50, should be watched to ensure that the infection does not result in complications. Emergency medical attention should be sought for trouble breathing, dehydration, and the confusion or lethargy that may accompany low oxygen levels, high fever or dehydration.
For additional information about swine flu and its symptoms, the Centers for Disease Control (CDC) have an excellent website.