https://en.wikipedia.org/wiki/Influenza_A_virus_subtype_H1N1

Influenza A virus subtype H1N1

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For the H1N1/09 virus strain responsible for the 2009 flu pandemic, see Pandemic H1N1/09 virus. For the 2009 pandemic Influenza A(H1N1), see 2009 flu pandemic. For the 1918 pandemic of Influenza A(H1N1), see 1918 flu pandemic.

Influenza (Flu)

Types
Avian (A/H5N1 subtype) Canine Equine Swine (A/H1N1 subtype)
Vaccines
2009 pandemic (Pandemrix) ACAM-FLU-A Fluzone Influvac Live attenuated (FluMist) Optaflu
Treatment
Amantadine Arbidol Laninamivir Oseltamivir Peramivir Rimantadine Vitamin D Zanamivir
Pandemics
2009 Swine 1968–1969 Hong Kong 1918
Outbreaks
2008 West Bengal 2007 Bernard Matthews H5N1 2007 Australian equine 2006 H5N1 India 1976 swine flu
See also
Flu season Influenza evolution Influenza research Influenza-like illness
v t e

'Influenza' A (H1N1) virus is a subtype of influenza A virus and was the most common cause of human influenza (flu) in 2009. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza. H1N1 (pronounced "HEE-NEE" by healthcare professionals) strains caused a small percentage of all human flu infections in 2004–2005.^[1] Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza).

In June 2009, the World Health Organization declared the new strain of swine-origin H1N1 as a pandemic. This strain is often called swine flu by the public media. This novel virus spread worldwide and had caused about 17,000 deaths by the start of 2010. On August 10, 2010, the World Health Organization declared the H1N1 influenza pandemic over, saying worldwide flu activity had returned to typical seasonal patterns.^[2]

As of 26 April 2011, an H1N1 pandemic preparedness alert has been issued by the World Health Organisation (WHO) for the Americas.^[3] The affected areas have included the Chihuahua region of Mexico where its severity and work load have been high. It is reported by the aforementioned Recombinomics source that the current vaccine (California/7/2009) for H1N1 influenza might be losing its effectiveness in 2011. This point is all the more significant since it is the current virus target for the northern hemisphere's flu vaccine, and is the intended choice for the southern hemisphere.

[hide]

[edit] Swine influenza

Swine influenza (also called swine flu, or pig flu) is an infection by any one of several types of swine influenza virus. Swine influenza virus (SIV) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2, and H2N3.

Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection. The meat of an infected animal poses no risk of infection when properly cooked.

Pigs experimentally infected with the strain of swine flu that is causing the current human pandemic showed clinical signs of flu within four days, and the virus spread to other uninfected pigs housed with the infected ones.^[4]

During the mid-20th century, identification of influenza subtypes became possible, allowing accurate diagnosis of transmission to humans. Since then, only 50 such transmissions have been confirmed. These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness, and general discomfort. The recommended time of isolation is about five days.

[edit] Notable incidents

[edit] Spanish flu

Main article: 1918 flu pandemic

The Spanish flu, also known as la grippe, La Gripe Española, or La Pesadilla, was an unusually severe and deadly strain of avian influenza, a viral infectious disease, that killed some 50 to 100 million people worldwide over about a year in 1918 and 1919. It is thought to be one of the most deadly pandemics in human history.

The 1918 flu caused an unusual number of deaths, possibly due to it causing a cytokine storm in the body.^[5]^[6] (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)^[7] The Spanish flu virus infected lung cells, leading to overstimulation of the immune system via release of cytokines into the lung tissue. This leads to extensive leukocyte migration towards the lungs, causing destruction of lung tissue and secretion of liquid into the organ. This makes it difficult for the patient to breathe. In contrast to other pandemics, which mostly kill the old and the very young, the 1918 pandemic killed unusual numbers of young adults, which may have been due to their healthy immune systems mounting a too-strong and damaging response to the infection.^[8]

The term "Spanish" flu was coined because Spain was at the time the only European country where the press were printing reports of the outbreak, which had killed thousands in the armies fighting World War I. Other countries suppressed the news in order to protect morale.^[9]

[edit] Fort Dix outbreak

Main article: 1976 swine flu outbreak

In 1976, a novel swine influenza A (H1N1) caused severe respiratory illness in 13 soldiers with 1 death at Fort Dix, New Jersey. The virus was detected only from January 19 to February 9 and did not spread beyond Fort Dix.^[10] Retrospective serologic testing subsequently demonstrated that up to 230 soldiers had been infected with the novel virus, which was a H1N1 strain. The cause of the outbreak is still unknown and no exposure to pigs was identified. ^[11]

[edit] Russian flu

The 1977–1978 Russian flu epidemic was caused by strain Influenza A/USSR/90/77 (H1N1). It infected mostly children and young adults under 23 because a similar strain was prevalent in 1947–57, causing most adults to have substantial immunity. Because of a striking similarity in the viral RNA of both strains – one which is unlikely to appear in nature due to antigenic drift – it is being speculated that the later outbreak was due to a laboratory incident in Russia or Northern China, though this is being denied by scientists in those countries.^[12]^[13]^[14] The virus was included in the 1978–1979 influenza vaccine.^[15]^[16]^[17]^[18]

See also Influenza A virus subtype H2N2#Russian flu for the 1889–1890 Russian flu

[edit] 2009 A(H1N1) pandemic

Illustration of influenza antigenic shift.

Main article: Pandemic H1N1/09 virus

In the 2009 flu pandemic, the virus isolated from patients in the United States was found to be made up of genetic elements from four different flu viruses – North American swine influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe – "an unusually mongrelised mix of genetic sequences."^[19] This new strain appears to be a result of reassortment of human influenza and swine influenza viruses, in all four different strains of subtype H1N1.

Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. The six genes from American swine flu are themselves mixtures of swine flu, bird flu, and human flu viruses.^[20] While viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S.^[21]

In April 2009, an outbreak of Influenza-like illness occurred in Mexico and the USA; the CDC reported seven cases of novel A/H1N1 influenza. By April 24 it became clear that the outbreak of ILI in Mexico and the confirmed cases of novel influenza A in the southwest US were related and WHO issued a health advisory on the outbreak of "influenza like illness in the United States and Mexico". ^[22] The disease then spread very rapidly, with the number of confirmed cases rising to 2,099 by May 7, despite aggressive measures taken by the Mexican government to curb the spread of the disease.^[23]

On June 11, 2009, the WHO declared an H1N1 pandemic, moving the alert level to phase 6, marking the first global pandemic since the 1968 Hong Kong flu.^[24]

On October 25, 2009 U.S. President Barack Obama officially declared H1N1 a national emergency^[25] Despite President Obama's concern, a Fairleigh Dickinson University PublicMind poll found in October 2009 that an overwhelming majority of New Jerseyans (74%) were not very worried or not at all worried about contracting the H1N1 flu virus.^[26] Though the President’s declaration caused many U.S. employers to take actions to help stem the spread of the swine flu and to accommodate employees and / or workflow which may be impacted by an outbreak. ^[27]

A study conducted in coordination with the University of Michigan Health Service is scheduled for publication in the December 2009 American Journal of Roentgenology warning that H1N1 flu can cause pulmonary embolism, surmised as a leading cause of death in this current pandemic. The study authors suggest physician evaluation via contrast enhanced CT scans for the presence of pulmonary emboli when caring for patients diagnosed with respiratory complications from a "severe" case of the H1N1 flu.^[28]

March 21, 2010 worldwide update by the U.N.'s World Health Organization (WHO) states that "213 countries and overseas territories/communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including at least 16,931 deaths." ^[29]

As of May 30, 2010 worldwide update by World Health Organization(WHO) more than 214 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 18,138 deaths. ^[30]

The research team of Andrew Miller MD showed pregnant patients are at increased risk.^[31] It has been suggested that pregnant women and certain populations such as native North Americans have a greater likelihood of developing a T helper type 2 response to H1N1 influenza which may be responsible for the systemic inflammatory response syndrome that causes pulmonary edema and death. [32

https://en.wikipedia.org/wiki/Influenza_A_virus_subtype_H1N1

Swine Flu
(Swine Influenza A [H1N1] Virus)

Swine Flu (H1N1) Vaccine Slideshow Pictures

Swine Flu (H1N1) FAQ Slideshow Pictures

Strep or Sore Throat Slideshow Pictures

Medical Author:

Charles Patrick Davis, MD, PhD

Medical Editor:

Melissa Conrad Stöppler, MD

What to Do if You Think You Have H1N1 Swine Flu Virus

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

What should you do if you think you have H1N1 swine flu? If you've got fever, cough, or one of the other symptoms of the flu, you may be wondering if you have contracted the H1N1 swine flu virus. The reality is that it isn't possible to know unless specialized testing is ordered, and for uncomplicated cases of the flu in non-hospitalized patients, routine testing for the H1N1 virus is not being carried out.

Experts recommend that people who suspect that they have H1N1 infection stay home and avoid contact with other people. The only time you should leave home is to access medical care if needed. That said, it is important to remember that the vast majority of flu cases (even H1N1 cases) produce only a mild illness for which doctor's visits and/or antiviral drugs are not necessary. So, the presence of cough and fever in an individual who is not at high risk for complications (see below) and who does not have warning signs of a medical emergency should not be a reason to visit an ER. The emergency department should be used for the treatment of people who are very sick or who have life-threatening emergencies (listed below). If you're in doubt, a call to your health-care practitioner can help you decide whether or not you need to access medical care.

Learn when to seek medical care for H1N1 swine flu symptoms »

Top Searched H1N1 Swine Flu Terms

H1N1 symptoms, treatment, H1N1 mutation, influenza, bird flu, H3N2, Spanish flu, H5N1, SARS, swine flu debacle 1976, swine flu vaccine side effects

The latest news on swine flu

What is swine flu (novel H1N1 influenza A swine flu)?

Swine flu (swine influenza) is a respiratory disease caused by viruses (influenza viruses) that infect the respiratory tract of pigs and result in nasal secretions, a barking-like cough, decreased appetite, and listless behavior. Swine flu produces most of the same symptoms in pigs as human flu produces in people. Swine flu can last about one to two weeks in pigs that survive. Swine influenza virus was first isolated from pigs in 1930 in the U.S. and has been recognized by pork producers and veterinarians to cause infections in pigs worldwide. In a number of instances, people have developed the swine flu infection when they are closely associated with pigs (for example, farmers, pork processors), and likewise, pig populations have occasionally been infected with the human flu infection. In most instances, the cross-species infections (swine virus to man; human flu virus to pigs) have remained in local areas and have not caused national or worldwide infections in either pigs or humans. Unfortunately, this cross-species situation with influenza viruses has had the potential to change. Investigators think the 2009 swine flu strain, first seen in Mexico, should be termed novel H1N1 flu since it is mainly found infecting people and exhibits two main surface antigens, H1 (hemagglutinin type 1) and N1 (neuraminidase type1). Recent investigations show the eight RNA strands from novel H1N1 flu have one strand derived from human flu strains, two from avian (bird) strains, and five from swine strains.

Why is swine flu (H1N1) now infecting humans?

Many researchers now consider that two main series of events can lead to swine flu (and also avian or bird flu) becoming a major cause for influenza illness in humans.

First, the influenza viruses (types A, B, C) are enveloped RNA viruses with a segmented genome; this means the viral RNA genetic code is not a single strand of RNA but exists as eight different RNA segments in the influenza viruses. A human (or bird) influenza virus can infect a pig respiratory cell at the same time as a swine influenza virus; some of the replicating RNA strands from the human virus can get mistakenly enclosed inside the enveloped swine influenza virus. For example, one cell could contain eight swine flu and eight human flu RNA segments. The total number of RNA types in one cell would be 16; four swine and four human flu RNA segments could be incorporated into one particle, making a viable eight RNA segmented flu virus from the 16 available segment types. Various combinations of RNA segments can result in a new subtype of virus (known as antigenic shift) that may have the ability to preferentially infect humans but still show characteristics unique to the swine influenza virus (see Figure 1). It is even possible to include RNA strands from birds, swine, and human influenza viruses into one virus if a cell becomes infected with all three types of influenza (for example, two bird flu, three swine flu, and three human flu RNA segments to produce a viable eight-segment new type of flu viral genome). Formation of a new viral type is considered to be antigenic shift; small changes in an individual RNA segment in flu viruses are termed antigenic drift and result in minor changes in the virus. However, these can accumulate over time to produce enough minor changes that cumulatively change the virus' antigenic makeup over time (usually years).

Second, pigs can play a unique role as an intermediary host to new flu types because pig respiratory cells can be infected directly with bird, human, and other mammalian flu viruses. Consequently, pig respiratory cells are able to be infected with many types of flu and can function as a "mixing pot" for flu RNA segments (see Figure 1). Bird flu viruses, which usually infect the gastrointestinal cells of many bird species, are shed in bird feces. Pigs can pick these viruses up from the environment and seem to be the major way that bird flu virus RNA segments enter the mammalian flu virus population.

Picture of antigenic shift and antigenic drift in swine flu (H1N1).

Figure 1.

What are the symptoms of swine flu (H1N1)?

Symptoms of swine flu are similar to most influenza infections: fever (100F or greater), cough, nasal secretions, fatigue, and headache, with fatigue being reported in most infected individuals. Some patients also get nausea, vomiting, and diarrhea. In Mexico, many of the patients are young adults, which made some investigators speculate that a strong immune response may cause some collateral tissue damage. Some patients develop severe respiratory symptoms and need respiratory support (such as a ventilator to breathe for the patient). Patients can get pneumonia (bacterial secondary infection) if the viral infection persists, and some can develop seizures. Death often occurs from secondary bacterial infection of the lungs; appropriate antibiotics need to be used in these patients. The usual mortality (death) rate for typical influenza A is about 0.1%, while the 1918 "Spanish flu" epidemic had an estimated mortality rate ranging from 2%-20%. Swine flu in Mexico (as of April 2009) has had about 160 deaths and about 2,500 confirmed cases, which would correspond to a mortality rate of about 6%, but these initial data have been revised and the mortality rate currently in Mexico is estimated to be much lower. By June 2009, the virus had reached 74 different countries on every continent except Antarctica, and by September 2009, the virus had been reported in most countries in the world. Fortunately, the mortality rate as of October 2009 has been low but higher than for the conventional flu (average conventional flu mortality rate is about 36,000 per year; projected novel H1N1 flu mortality rate is 90,000 per year in the U.S. as determined by the president's advisory committee).

How is swine flu (H1N1) diagnosed?

Swine flu is presumptively diagnosed clinically by the patient's history of association with people known to have the disease and their symptoms listed above. Usually, a quick test (for example, nasopharyngeal swab sample) is done to see if the patient is infected with influenza A or B virus. Most of the tests can distinguish between A and B types. The test can be negative (no flu infection) or positive for type A and B. If the test is positive for type B, the flu is not likely to be swine flu (H1N1). If it is positive for type A, the person could have a conventional flu strain or swine flu (H1N1). However, the accuracy of these tests has been challenged, and the U.S. Centers for Disease Control and Prevention (CDC) has not completed their comparative studies of these tests. However, a new test developed by the CDC and a commercial company reportedly can detect H1N1 reliably in about one hour; as of October 2009, the test is only available to the military.

Swine flu (H1N1) is definitively diagnosed by identifying the particular antigens associated with the virus type. In general, this test is done in a specialized laboratory and is not done by many doctors' offices or hospital laboratories. However, doctors' offices are able to send specimens to specialized laboratories if necessary. Because of the large number of novel H1N1 swine flu cases (as of October 2009, the vast majority of flu cases [about 99%] are due to novel H1N1 flu viruses), the CDC recommends only hospitalized patients' flu virus strains be sent to reference labs to be identified.

CDC developed PCR diagnostic test to detect novel H1N1 virus.

The CDC developed a PCR diagnostic test to detect novel H1N1 virus. Photo courtesy of the CDC

What are the symptoms of swine flu (H1N1)?

How is swine flu (H1N1) diagnosed?

The CDC developed a PCR diagnostic test to detect novel H1N1 virus. Photo courtesy of the CDC

What treatment is available for swine flu (H1N1)?

The best treatment for influenza infections in humans is prevention by vaccination. Work by several laboratories has recently produced vaccines. The first vaccine released in early October 2009 was a nasal spray vaccine. It is approved for use in healthy individuals ages 2 through 49. This vaccine consists of a live attenuated H1N1 virus and should not be used in anyone who is pregnant or immunocompromised. The injectable vaccine, made from killed H1N1, became available in the second week of October. This vaccine is approved for use in ages 6 months to the elderly, including pregnant females. Both of these vaccines have been approved by the CDC only after they had conducted clinical trials to prove that the vaccines were safe and effective. However, caregivers should be aware of the vaccine guidelines that come with the vaccines, as occasionally, the guidelines change. Please see the sections below titled "Can novel H1N1 swine flu be prevented with a vaccine?" and the timeline update for the current information on the vaccines.

Two antiviral agents have been reported to help prevent or reduce the effects of swine flu. They are zanamivir (Relenza) and oseltamivir (Tamiflu), both of which are also used to prevent or reduce influenza A and B symptoms. These drugs should not be used indiscriminately, because viral resistance to them can and has occurred. Also, they are not recommended if the flu symptoms already have been present for 48 hours or more, although hospitalized patients may still be treated past the 48-hour guideline. Severe infections in some patients may require additional supportive measures such as ventilation support and treatment of other infections like pneumonia that can occur in patients with a severe flu infection. The CDC has suggested in their interim guidelines that pregnant females can be treated with the two antiviral agents.

Oseltamivir (Tamiflu) is an antiviral agent that may prevent or reduce influenza A and B symptoms. Photo courtesy of the CDC

Zanamivir (Relenza) has been reported to help prevent or reduce the effects of swine flu. Photo courtesy of the CDC

What is the history of swine flu (H1N1) in humans?

In 1976, there was an outbreak of swine flu at Fort Dix. This virus is not the same as the 2009 outbreak, but it was similar insofar as it was an influenza A virus that had similarities to the swine flu virus. There was one death at Fort Dix. The government decided to produce a vaccine against this virus, but the vaccine was associated with neurological complications (Guillain-Barré syndrome) and was discontinued. Some individuals speculate that formalin, used to inactivate the virus, may have played a role in the development of this complication in 1976. There is no evidence that anyone who obtained this vaccine would be protected against the 2009 swine flu. One of the reasons it takes a few months to develop a new vaccine is to test the vaccine for safety to avoid the complications seen in the 1976 vaccine. New vaccines against any flu virus type are usually made by growing virus particles in eggs. A serious side effect (allergic reaction such as swelling of the airway) to vaccines can occur in people who are allergic to eggs; these people should not get flu vaccines. Individuals with active infections or diseases of the nervous system are also not recommended to get flu vaccines.

Can novel H1N1 swine flu be prevented with a vaccine?

The best way to prevent novel H1N1 swine flu would be the same best way to prevent other influenza infections, and that is vaccination. The CDC has multiple recommendations for vaccination based on who should obtain the first doses when the vaccine becomes available (to protect the most susceptible populations) and according to age groups. The CDC based the recommendations on data obtained from vaccine trials and infection reports gathered over the last few months. The current (October 2009) vaccine recommendations from the CDC say the following groups should get the vaccine as soon as it is available:

pregnant women,

people who live with or provide care for children younger than 6 months of age,

health-care and emergency medical services personnel,

people between 6 months and 24 years of age, and

people from the ages of 25 through 64 who are at higher risk because of chronic health disorders such as asthma, diabetes, or a weakened immune system.

Currently, the CDC is stating that people ages 10 and above are likely to need only one vaccine shot to provide protection against novel H1N1 swine flu and further suggest that these shots will be effective in about 76% of people who obtain the vaccine. New vaccine trial data showed that healthy adults produce protective antibodies in about 98% of people in 21 days. Unfortunately, the vaccine shot in children ages 6 months to 9 years of age is not as effective as it is in older children and adults. Consequently, the CDC currently recommends that for ages 6 months up to and including 9 years of age, the children obtain two shots of the novel H1N1 vaccine, the second shot 21 days after the first shot.

Pregnant women are strongly suggested to get vaccinated as stated above. Although some vaccine preparations (multidose vials) contain low levels of thimerosal preservative (a mercury-containing preservative), the CDC still considers the vaccine safe for the fetus and mother. However, some vaccine preparations that are in single-dose vials will not have thimerosal preservative, so those pregnant individuals who are concerned about thimerosal can get this vaccine preparation when it is available.

Another type of vaccine (currently named Influenza A [H1N1] 2009 Monovalent Vaccine Live, Intranasal) has been made available during the first week in October 2009. It is a live attenuated novel H1N1 flu vaccine that contains no thimerosal, is produced by MedImmune, LLC, and is sprayed into the nostrils. This vaccine is only for healthy people 2-49 years of age, and some data suggest that it is less effective in generating an immune response in adults than the vaccine injection. The dosing schedule is as follows:

Children 2-9 years of age should receive two doses (0.1 ml in each nostril; total equals 0.2 ml per dose) -- the second dose should be given the same way about one month after the first dose

Children, adolescents and adults, 10-49 years of age should receive one dose -- (0.1 ml in each nostril; total equals 0.2 ml per dose)

The CDC occasionally makes changes and updates its information on vaccines and other recommendations about the current flu pandemic. The CDC states, "for the most accurate health information, visit http://www.cdc.gov or call 1-800-CDC-INFO, 24/7." Caregivers should check the vaccine package inserts for more detailed information on the vaccines when they become available. This article has an updated timeline for novel H1N1 swine flu attached (see below) and provides the reader with current details about the pandemic. The following is a list of the CDC-approved H1N1 vaccines and the companies that name and manufacture them as of 10/29/09:

Influenza A (H1N1) 2009 Monovalent Vaccine by Sanofi Pasteur

Influenza A (H1N1) 2009 Monovalent Vaccine by Novartis

Influenza A (H1N1) 2009 Monovalent Vaccine Live, Intranasal by MedImmune, LLC

Influenza A (H1N1) 2009 Monovalent Vaccine by CSL Limited

The CDC says that a good way to prevent any flu disease is to avoid exposure to the virus; this is done by frequent hand washing, not touching your hands to your face (especially the nose and mouth), and avoiding any close proximity to or touching any person who may have flu symptoms. Since the virus can remain viable and infectious for about 48 hours on many surfaces, good hygiene and cleaning with soap and water or alcohol-based hand disinfectants are also recommended. Some physicians say face masks may help prevent getting airborne flu viruses (for example, from a cough or sneeze), but others think the better use for masks would be on those people who have symptoms and sneeze or cough. The use of Tamiflu or Relenza may help prevent the flu if taken before symptoms develop or reduce symptoms if taken within about 48 hours after symptoms develop. Some investigators say that administration of these drugs is still useful after 48 hours, especially in high-risk patient populations .However, taking these drugs is not routinely recommended for prevention for the healthy population because investigators suggest that as occurs with most drugs, flu strains will develop resistance to these medications. Recently, the CDC made further suggestions about the use of these antiviral medications. Dr. Schuchat, a CDC official, indicated that three modifications were being suggested (Sept. 8, 2009) to the interim guidelines for use of Tamiflu and Relenza:

Your doctor should be consulted before these drugs are prescribed.

In general, preventive measures to prevent the spread of flu are often undertaken by those people who have symptoms. Symptomatic people should stay at home, avoid crowds, and take off from work or school until the disease is no longer transmittable (about two to three weeks) or until medical help and advice is sought. Sneezing, coughing, and nasal secretions need to be kept away from other people; simply using tissues and disposing of them will help others. Quarantining patients is usually not warranted, but such measures depend on the severity of the disease. The CDC recommends that people who appear to have an influenza-like illness upon arrival at work or school or become ill during the day be promptly separated from other people and be advised to go home until at least 24 hours after they are free of fever (100 F [37.8 C] or greater), or signs of a fever, without the use of fever-reducing medications. The novel H1N1 swine flu disease takes about seven to 10 days before fevers stop, but new research data (Sept. 14, 2009) suggests waiting until the cough is gone since many people are still infectious about one week after fever is gone. The CDC has not yet extended their recommendations to stay home for that extra week.

Can H1N1 be prevented if the H1N1 flu vaccine is not readily available?

Although vaccination is the best way to "prevent" H1N1, currently (November 2009), there is not enough available for everyone who wants or needs H1N1 vaccination. Until H1N1 vaccine supplies meet demand, there are some things people can do to try and prevent infection. Without vaccination, the best strategy is to not allow H1N1 virus to contact a person's mucus membranes because if the virus does not reach cells in which it can grow, it cannot cause infection. Quarantining H1N1-infected people is an extreme measure that may work in some instances (for example, China uses this method), but even with quarantining, the virus may still spread by people who have minimal or no symptoms.

The next step that is easier to be implemented by individuals is for people with the disease to self-quarantine until they become noninfectious (about seven to 10 days after flu symptoms abate). Infected people can wear surgical masks to reduce the amount of droplet spray from coughs and sneezes and throw away contaminated tissues. Unfortunately, these approaches depend on the compliance of many other people, and the likelihood that such methods will be highly successful in preventing H1N1 infections, at best, is only fair. Such methods have not stopped the current pandemic. Yet there are still some other methods available to individuals. Perhaps the best way for individuals to try to prevent H1N1 infection is a combination of methods that are aimed at fulfilling the very basic principle that if H1N1 doesn't reach an individual's mucus membrane cells, infection will be prevented. The methods are as follows:

These seven steps can help prevent individuals from getting H1N1 infection, but for many people, adherence to them may be difficult at best. However, there are some additional strategies that may also help prevent H1N1 infections in unvaccinated people according to some investigators. Saline nasal washes and gargling with saline (or a commercial product) as a way to reduce or eliminate H1N1 virus from mucus membranes has been suggested. Proponents of these methods base their rationale on the fact that flu viruses usually take about two to three days to proliferate in nasal/throat cells. While nasal washes and gargling may be soothing to some people, there are no studies that indicate H1N1 is killed, inactivated, or completely removed by these methods; conversely, there are no data suggesting these methods cannot have any effect on H1N1. However, with long-term nasal washes using Neti pots, sinus infection with other pathogens may be encouraged.

Other investigators and physicians have offered additional methods that may help reduce exposure to H1N1 virus. For example, Dr. Gerberding, a former CDC director, had several suggestions about how to avoid H1N1 infection on an airplane. She suggested the following:

HEPA

Variations of her suggestions may be applicable in many different social, work, or travel situations, but there are no data to prove these methods are effective. In addition, common-sense precautions such as not drinking or eating things touched by others, avoiding casual physical contacts (for example, handshakes, social hugs or kisses, public water fountains [these are OK if you touch nothing and lips only touch flowing water], banisters on stairways, and restroom door handles) will limit exposure to H1N1. Again, these common sense suggestions lack data substantiation.

Many investigators suggest that people stay well hydrated, take vitamins, and get plenty of rest, but these precautions will not prevent H1N1 infections although they may help reduce the effects of infection by strengthening the person's immune system to fight infection. Similarly, current antiviral medications (described in the preceding section) act on H1N1 viruses that have already infected cells; they work by preventing or reducing viral particles from aggregating and being released from infected cells. Timing is important; if only a few cells are infected and the antiviral medications are administered quickly (usually before flu symptoms develop or within 48 hours), the viruses are reduced in number (they cannot easily bud out from the cell surface), so few, if any, other respiratory or mucus membrane cells become infected. This can result in either no flu symptoms or, if a larger number of cells were initially infected, less severe symptoms. The overall effect for the person is that the H1N1 infection was prevented (it was not; the symptoms were prevented from developing) or that symptoms were reduced.

In the strictest sense of the word prevention, even effective vaccines do not "prevent" infections. What they do accomplish is to alert the immune system to be on guard for certain antigens that are associated with a pathogen (for example, H1N1 virus, pneumococcal bacteria). When the pathogen first infects the host, its antigens are recognized, and these cause a rapid immunoprotective response to occur that prevents the pathogen from proliferating and developing symptoms in the host. People, including physicians and researchers, often term this complex response to vaccination as "prevention of infection" but what actually occurs is the prevention of further infection so well that symptoms do not develop or are minimal in the host.

In summary, if H1N1 viruses fail to contact cells they can infect, the disease will be prevented. As stated above, this is difficult, but not impossible, to do in almost all societies. Prevention of H1N1 symptoms of infection is possible with antiviral medications if these are given very early in the infection. There are many other methods that may reduce the chance of getting the virus on a person's mucosal surface, but most methods have not been backed up with objective data. Most doctors and investigators suggest that items that help boost or allow the immune response to function well will help people resist H1N1 infections and reduce symptoms, but these also do not prevent infections. Consequently, while waiting for H1N1 vaccine, these are some ways individuals can improve their chances of preventing or reducing the symptoms of H1N1 infections.

Is swine flu (H1N1) a cause of an epidemic or pandemic in 2009?

An epidemic is defined as an outbreak of a contagious disease that is rapid and widespread, affecting many individuals at the same time. The swine flu outbreak in Mexico fit this definition. A pandemic is an epidemic that becomes so widespread that it affects a region, continent, or the world. As of April 2009, the H1N1 swine flu outbreak did not meet this definition. However, as of June 11, 2009, WHO officials determined that H1N1 2009 influenza A swine flu reached WHO level 6 criteria (person-to-person transmission in two separate WHO-determined world regions) and declared the first flu pandemic in 41 years. To date, the flu has reached over 74 different countries on every continent except Antarctica in about three month's time; fortunately, the severity of the disease has not increased.

What is the prognosis (outlook) for patients who get swine flu (H1N1)?

The following is speculation on the prognosis for swine flu (H1N1) because this disease has only been recently diagnosed and the data is changing daily. This section is based on currently available information.

In general, the majority (about 90%-95%) of people who get the disease feel terrible (see symptoms) but recover with no problems, as seen in patients in both Mexico and the U.S. Caution must be taken as the swine flu (H1N1) is still spreading and has become a pandemic. So far, young adults have not done well, and in Mexico, this group currently has the highest mortality rate, but this data could quickly change.

People with depressed immune systems historically have worse outcomes than uncompromised individuals; investigators suspect that as swine flu (H1N1) spreads, the mortality rates may rise and be high in this population. Current data suggest that pregnant individuals, children under 2 years of age, young adults, and individuals with any immune compromise or debilitation are likely to have a worse prognosis. Unfortunately, the problem with the prognosis is still unclear. If the mortality is like the conventional flu that causes mortality rates of about 0.1%, the result would be about 36,000 deaths per year because of the huge number of people who get infected. If the Mexico swine flu (H1N1) ends up with a mortality rate of about 6% and infects the same number of millions of people as conventional flu viruses, the projected numbers could be as high as 2 million deaths in the U.S. alone. This is a bad prognosis for about 2 million people and their families; these potential deaths are major reasons that health officials are so concerned about the spread of this new virus. As of September 2009, the current estimates are that about 90,000 deaths will occur in the U.S. from novel H1N1 swine flu (estimated by the president's advisory committee). As of October, these estimates have not been revised by the advisory committee or the CDC.

Another confounding problem with the prognosis of swine flu (H1N1) is that the disease is occurring and spreading in high numbers at the usual end of the flu season. Most flu outbreaks happen between November to the following April, with peak activity between late December to March. This outbreak is not following the usual flu pattern since novel H1N1 began its outbreak in April and had spread throughout the world by September. Some scientists think that swine flu (H1N1) will die down but return with many more cases in the fall, and still others speculate the current pandemic will eventually resemble the outcomes similar to the 1918 influenza pandemic. Some suggest it may resemble the SARS (severe acute respiratory syndrome caused by a coronavirus strain) outbreak in 2002-2003 in which the disease spread to about 10 countries with over 7,000 cases, over 700 deaths, and had a 10% mortality rate. Effective isolation of patients was done in this case, and many investigators think the outbreak was stopped due to this measure. Because swine flu (H1N1) is a new virus and does not seem to be following the usual flu disease pattern, any prognosis is speculative, although as of October 2009, the numbers of people with flu-like illness are higher than usual and the illness is affecting a much younger population than the conventional flu. As the pandemic progresses, this article will be updated. The best news about this novel H1N1 swine flu is that the majority of people, as of October 2009, who have caught the flu recover without medical treatment and have an excellent prognosis.

http://www.medicinenet.com/swine_flu/article.htm

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Wednesday, April 4, 2012

H1N1 virus

Influenza A virus subtype H1N1

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[edit] Swine influenza