H1N1 is a subtype of the type A influenza virus that causes an illness commonly known as the flu. There are three types of influenza virus (A, B, and C), and each type may have various subtypes. New strains may develop when the virus mutates. The H1N1 subtype currently holds much interest because an ongoing pandemic involves a novel (new) strain of the virus. This outbreak began in late March of 2009 in Mexico and is predicted to continue into the regular flu season of 2009-10.
This novel strain was originally referred to as "swine flu" because it appeared similar to influenza viruses that normally infect pigs (swine) and rarely infect humans. There was widespread concern that eating pork or coming into contact with pigs would increase the risks of contracting the novel H1N1 flu. Because people began to avoid pork for fear of catching H1N1, the pork industry suffered. Travel to Mexico was restricted, which also had negative economic effects. In late April 2009, 300,000 pigs were slaughtered in Egypt in an effort to curb the disease, even though no cases of H1N1 had been reported in Egypt at that time.
Later studies showed that this novel H1N1 strain (henceforth, H1N1 or novel H1N1) is quite distinct from influenza viruses that normally infect pigs. It appears that the virus is derived from multiple viruses that may have originated in swine. Novel H1N1 is spread from humans to humans and is not known to be transmitted by eating pork or from close contact with swine. It has not yet been identified in pigs in the United States, and only isolated herds of swine have been infected around the world. Thus, the term "swine flu" is somewhat of a misnomer. Nonetheless, it is still currently used to refer to novel H1N1.
According to the U.S. Centers for Disease Control (CDC), as of September 2009, around 9,000 people in the United States have been hospitalized due to novel H1N1 infection, and fewer than 600 deaths are linked to this new virus. It is estimated that a total of one million people have contracted H1N1 flu in the United States. This is far less than the number of cases caused by seasonal flu viruses, which infect an average of 5-20% of the U.S. population (up to 60 million people) each year. Annually, seasonal flu viruses cause around 200,000 severe cases (requiring hospitalization) and 36,000 deaths. However, what makes H1N1 influenza unique is that infections peaked outside of the regular flu season, and it is currently the predominant strain of the influenza virus worldwide.
Another unique feature of novel H1N1 influenza is that more infections occur in people under age 60. With seasonal flu, the above-60 population is usually considered to be at high risk. However, the elderly seem to be more resistant to novel H1N1 infection, perhaps because previous exposure to similar viruses has increased their immunity to this new strain. However, people with lower immunity are still at increased risk of infection for any strain of flu, as well as serious complications. This includes young children and those with certain health conditions that hinder the immune system, including cancer, human immunodeficiency virus (HIV), and acquired immunodeficiency syndrome (AIDS). Children also easily spread the virus to others due to poor hygiene, such as sneezing without covering the nose.
As with seasonal influenza viruses, novel H1N1 flu is transmitted through the air in tiny droplets when someone with the infection coughs, sneezes, or talks. Individuals are then exposed to the virus through inhalation, or by contact with objects such as telephones, door handles, railings, or computer keyboards. An infection may occur when the virus is then transferred to the eyes, nose, or mouth.
The symptoms of novel H1N1 flu are similar to those of seasonal flu. In fact, novel H1N1 has thus far caused milder symptoms than seasonal flu. Treatment for the flu, regardless of strain, includes bed rest and plenty of fluids, along with symptomatic treatment, such as drugs to fight viral infections, reduce fever, and help with sore throat and cough. An annual influenza vaccine may offer protection against some strains of the influenza virus. Other forms of prevention include frequent hand washing, avoiding touching the nose or face, and avoiding contact with infected individuals.
When a flu epidemic occurs, specific populations are infected with a type of influenza virus that has not been encountered before. Epidemics may be restricted to one locale (an outbreak), or they may be more general (an "epidemic") or even global (a pandemic). Because novel H1N1 influenza is causing infections globally, it is currently classified as a pandemic. However, the rates of infection have been far less than well-known pandemics, such as the 1918 "Spanish flu" pandemic that killed between 50 and 100 million people worldwide. Both the current pandemic and the 1918 pandemic are attributed to the H1N1 subtype. Therefore, global health experts are advising caution for the upcoming flu season.
In the southern hemisphere, the seasonal flu period is between April and November. By late August of 2009, the levels of influenza (including H1N1) had returned to normal in the southern hemisphere, according to the World Health Organization.

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