Last year, the C.D.C. added middle-aged healthy people to the list of those at higher than usual risk of flu complications after studies showed that hospitalizations and deaths associated with the flu start rising considerably at age 50.
Anthrax illness begins with symptoms usually associated with the flu -- fever, lack of energy, and muscle aches -- but inhalation anthrax then manifests itself with severe breathing problems and shock.
"Carbon monoxide poisoning is called 'the great imitator,' " he said, explaining that the symptoms of carbon monoxide poisoning -- headache, nausea and muscle weakness -- are the same symptoms commonly associated with the flu.
Most impressively, Google Flu Trends, an application that tracks users' "Googling" words associated with the flu, such as "flu symptoms", "flu remedies", and "flu vaccines", tightly matches the Center for Disease Control and Prevention's (CDC) official flu tracking, which is based on Doctor and hospital survey data that have to be returned to and compiled by the CDC, with one major difference.
The CDC estimates deaths associated with the flu number between 3,000 and 49,000 people each year.
It's interesting to note that many of the body's defenses that attack the virus also cause many of the symptoms associated with the flu.
People with the flu are advised to get plenty of rest, drink plenty of liquids, avoid using alcohol and tobacco and, if necessary, take medications such as acetaminophen (paracetamol) to relieve the fever and muscle aches associated with the flu.
Qualitative and quantitative differences in humoral and cellular immune responses associated with the flu vaccination in 2009/2010 (pandemic H1N1 vaccine) and natural infection have not yet been described in detail.
These symptoms, which are commonly associated with the flu, can also indicate an early HIV infection.
The fever associated with the flu can range from 100° to 102°F, and even higher in children.
