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2009 swine flu pandemic

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Template:WebSlice-begin Template:2009 swine flu outbreak table Template:WebSlice-end The 2009 swine flu outbreak is an epidemic that began in April 2009 with a new strain of influenza virus. The new strain is commonly referred to as swine flu however some authorities object to the name and it is also refered to by other names such as Mexican flu. swine-origin influenza, and 2009 H1N1 flu The outbreak is believed to have started in March 2009 and was classified as meeting the criteria for the World Health Organization pandemic Phase 5 status on 29 April. Local outbreaks of an influenza-like illness were first detected in three areas of Mexico, but the virus responsible was not clinically identified as a new strain until April 24, 2009. Following the identification, its presence was soon confirmed in various Mexican states and in Mexico City. Within days, isolated cases (and suspected cases) were identified elsewhere in Mexico, the U.S., and several other Northern Hemisphere countries.

By April 28, the new strain was confirmed to have spread to Spain, the United Kingdom, New Zealand, and Israel, and the virus was suspected in many other nations, with a total in the aggregate of over 3,000 candidate cases, prompting the World Health Organization (WHO) to change its pandemic alert phase to "Phase 5", which denotes "widespread human infection". Despite the scale of the alert, the WHO stated on April 29 that the majority of people infected with the virus have made a full recovery without need of medical attention or antiviral drugs.

The new strain is an apparent reassortment of four strains of influenza A virus subtype H1N1. Analysis at the United States Centers for Disease Control and Prevention (CDC) identified the four component strains as one endemic in humans, one endemic in birds, and two endemic in pigs (swine). One swine strain was widespread in the United States, the other in Eurasia.

In late April both the United Nations WHO and the U.S. CDC expressed serious concern about the situation, as it had the potential to become a flu pandemic due to the novelty of the influenza strain, its transmission from human to human, and the unusually high mortality rate in Mexico. On April 25, 2009, the WHO formally determined the situation to be a "public health emergency of international concern", with knowledge lacking in regard to "the clinical features, epidemiology, and virology of reported cases and the appropriate responses". Government health agencies around the world also expressed concerns over the outbreak and are monitoring the situation closely.

On April 24, 2009, Mexico's schools, universities, and all public events were closed until May 6, 2009. On April 27, 2009, a few schools in the U.S. closed due to confirmed cases in students. On April 29, 2009 18 more U.S. schools shut down as the disease became more widespread in the U.S.

Prior influenza season

Template:Globalize/USA Prior to the outbreak, the Northern Hemisphere winter of 2008–2009 had been a comparatively mild season for flu infections, which typically cause 250,000–500,000 deaths worldwide yearly, mostly in the elderly, the very young, and persons with chronic illness. Up to April 8, 2009, the U.S. CDC had reported the deaths of 43 children from seasonal flu, compared to 68 in the previous flu season. The improvement was attributed, in part, to an improved Northern Hemisphere winter of 2008–2009 seasonal flu vaccine, for which a rare decision had been made to update all three strains (H1, H3, and B) simultaneously, which ultimately yielded a very good match to the strains of H1N1 and H3N2 which eventually circulated. (This followed the poor performance of the 2007–2008 vaccine, which offered only 2–20% protection rather than the 70–90% achieved in some years.) The U.S. improvement was also attributed to new recommendations there including the vaccination of people 5–18 years of age, who potentially act as "super-spreaders" due to failure to take precautions such as hand-washing.

Initial outbreaks

Further information: 2009 swine flu outbreak timeline
Main symptoms of swine flu in humans

The earliest confirmed case of the illness was in the town of La Gloria, Veracruz, Mexico, with 5 year old Édgar Enrique Hernández, considered to possibly be patient zero. Beginning in early March, a flu that progressed in many cases to respiratory illness affected 60% of La Gloria's residents; however, no further cases of swine flu have been confirmed in the town. La Gloria is located near a pig farming operation that raises nearly one million pigs per year, and town residents have long been bothered by flies that multiply in the pig farm's manure lagoons. The Mexican Social Security Institute stated in early April that these flies may have been the original disease vector of the virus. The owner of the pig farm, Smithfield Foods, has stated that it had found no clinical signs or symptoms of the presence of swine influenza in the company's swine herd, nor in its employees at its joint ventures in Mexico, and that it routinely administers influenza virus vaccination to their swine herds and conducts monthly testing for the presence of swine influenza.

The outbreak was first detected in Mexico City, where surveillance began picking up a surge in cases of influenza-like illness (ILI) starting March 18. The surge was assumed by Mexican authorities to be "late-season flu" (which usually coincides with a mild Influenzavirus B peak) until April 21, when a U.S. Centers for Disease Control and Prevention alert concerning two isolated cases of a novel swine flu was reported in the media. The first two cases identified (and confirmed) as swine flu were two children living in the United States, in San Diego County and Imperial County, California, who became ill on March 28 and 30. This new strain was promptly confirmed in Mexico, connecting the new strain to the ongoing outbreak of ILI. The first death from swine flu occurred on April 13, when a diabetic woman from Oaxaca died from respiratory complications. Some samples were sent to the U.S.-based CDC on April 18.

In March and April 2009, over 1000 cases of suspected swine flu in humans were detected in Mexico and the southwestern United States. The strain appears to be unusually lethal in Mexico. Although there have been reports of 152 "probable deaths" in Mexico City and "more than 100 dead from swine flu", the WHO had received reports of only 7 confirmed deaths total and explicitly denied the larger figure as of April 29.

There have also been cases reported in the states of San Luis Potosí, Hidalgo, Querétaro and Mexico State. Some cases in Mexico and the United States have been confirmed by the World Health Organization to be a new strain of H1N1. The Mexican fatalities are mainly young adults of 25 to 45, a common trait of pandemic flu. Mexican Health Minister José Ángel Córdova on April 24, said "We’re dealing with a new flu virus that constitutes a respiratory epidemic that so far is controllable."

Genetics and effects

Negative stain electronic microscope image of a reassorted A(H1N1) flu virus.

The CDC has confirmed that U.S. cases were 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." Pigs have been shown to act as a potential "mixing vessel" in which reassortment can occur between flu viruses of several species. This new strain appears to be a result of the reassortment of two swine influenza viruses, which themselves are descended from previous reassortments in pigs. Influenza viruses readily undergo reassortment because their genome is split between eight pieces of RNA (see Orthomyxoviridae). The virus was resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).

Pigs can harbor influenza viruses adapted to humans and others adapted to birds, allowing the viruses to exchange genes and create a pandemic strain.

Gene sequences for every viral gene were made available through the Global Initiative on Sharing Avian Influenza Data (GISAID), and were released to the general public via the National Center for Biotechnology Information a few days later. 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. 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. The seasonal influenza strain H1N1 vaccine is thought to be unlikely to provide protection.

The CDC does not fully understand why the U.S. cases were primarily mild disease while the Mexican cases had led to multiple deaths. However, research on previous pandemic strains has suggested that mortality can vary widely between different countries, with mortality being concentrated in the developing world. Differences in the viruses or co-infection are also being considered as possible causes. Of the fourteen initial samples from Mexico tested by the CDC, seven were found to match the American strain. The virus likely passes through several cycles of infection with no known linkages between patients in Texas and California, and that containment of the virus is "not very likely". The U.S. embassy reported that a CDC investigative team arrived in Mexico City on April 25 to work with Mexican counterparts to study the virus.

At a press briefing on April 27, acting CDC director Dr. Richard Besser stated that out of 40 confirmed cases in the United States at that point, only one individual was hospitalized. He also revealed that the median age was 16 years "with a range in age of 7 to 54 years." By April 29, the U.S. had 91 confirmed cases with 5 hospitalizations and one death.

Whereas most influenza strains affect the elderly and young children worst, this strain has primarily caused deaths in people between the ages of 25 and 50.

Pandemic concern

See also: Pandemic Severity Index

The WHO and CDC are concerned that this outbreak may become a pandemic, for the following reasons.

New strain

The virus is a new strain of influenza, from which human populations have not been vaccinated or naturally immunized.

Widespread human transmission

The virus infects by human-to-human transmission. Investigations of infected patients indicated no direct contact with swine, such as at a farm or agricultural fair. The strain was later confirmed to have been transmitted between humans. In contrast, for example, disease transmission in the last severe human outbreak of influenza, the bird flu that peaked in 2006, was determined to be almost entirely from direct contact between humans and birds.

Virulence

For reasons not yet well understood, all but one of the fatalities to date have been in Mexico. Furthermore, in Mexico (but not elsewhere) the reported deaths from the illness have primarily been young, healthy adults. Most other influenza strains produce the worst symptoms in young children, the elderly, and others with weaker immune systems. However, the CDC has indicated that symptoms reported from this strain so far are similar to those of normal seasonal flu. While some media outlets have speculated that this virus could cause a cytokine storm in patients, there is presently no evidence for this hypothesis, with the CDC stating that there is "insufficient information to date about clinical complications of this variant of swine-origin influenza A (H1N1) virus infection."

Lack of data

That other crucial factors are still largely unknown, such as transmission rates and patterns (epidemicity) and effectiveness of current influenza treatments, combined with the innate unpredictability of influenza strains, means that reliable forecasts cannot be made.

As noted, predicting the size and severity of influenza outbreaks is a very inexact science. The U.S. government was famously wrong in predicting, in 1976, a swine flu pandemic that never materialized.

In a statement, the WHO said "Because there are human cases associated with an animal influenza virus, and because of the geographical spread of multiple community outbreaks, plus the somewhat unusual age groups affected, these events are of high concern".

WHO Alert Phases

WHO Pandemic Influenza Phases (2009)
Phase Description
Phase 1 No animal influenza virus circulating among animals have been reported to cause infection in humans.
Phase 2 An animal influenza virus circulating in domesticated or wild animals is known to have caused infection in humans and is therefore considered a specific potential pandemic threat.
Phase 3 An animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks.
Phase 4 Human to human transmission of an animal or human-animal influenza reassortant virus able to sustain community-level outbreaks has been verified.
Phase 5 The same identified virus has caused sustained community level outbreaks in two or more countries in one WHO region.
Phase 6 In addition to the criteria defined in Phase 5, the same virus has caused sustained community level outbreaks in at least one other country in another WHO region.
Post peak period Levels of pandemic influenza in most countries with adequate surveillance have dropped below peak levels.
Post pandemic period Levels of influenza activity have returned to the levels seen for seasonal influenza in most countries with adequate surveillance.

Phase 3

The WHO decided not to raise the level of the worldwide pandemic alert after its first meeting, on April 25. A Phase 3 alert means that a new virus has been confirmed but there is no or limited evidence of human-to-human transmission - insufficient to sustain community-level outbreaks. The Phase 3 alert was initially set due to the avian flu.

Phase 4

Following the second meeting of the Emergency Committee on April 27, the pandemic alert level was raised to Phase 4. Phase 4, "Sustained Human to Human Transmission," entails community-wide outbreaks.

As of April 29, World Health Organization acting assistant director-general Dr. Keiji Fukuda stated:

moving closer to Phase 5. What we are trying to do right now is make absolutely sure that we are dealing with sustained transmission in at least two or more countries.

Phase 5

On April 29, WHO raised the pandemic alert level to five, the second-highest level, indicating that a pandemic is "imminent". Human-to-human transmission cases have been recorded in multiple regions. In Spain, officials confirmed the first European case of an infection in a person who had not traveled to Mexico, but whose girlfriend had.

Prevention and treatment

Further information: ]

Recommendations to prevent infection by the virus consist of the standard personal precautions against influenza. This includes frequent washing of hands with soap and water or with alcohol-based hand sanitizers, especially after being out in public. The CDC advises not touching the mouth, nose or eyes, as these are primary modes of transmission. When coughing, they recommend coughing into a tissue and disposing of the tissue, then immediately washing the hands.

There is no risk of flu transmission from consumption of pork.

Many countries confirmed that inbound international passengers will be screened. Typical airport health screening involves asking passengers which countries they have visited and checking whether they feel or appear particularly unwell. Thermographic equipment was put into use at a number of airports to screen passengers. In the USA, two confirmed cases were detected through their border infectious disease surveillance. A number of countries advised against travel to known affected regions.

The previously recommended influenza vaccines for the southern and northern hemispheres, including that for the 2009/2010 flu season, are ineffective against the new strain. Current development, large-scale manufacturing, distribution and delivery of a new vaccine takes several months, though the first doses could be ready as early as June 2009. The WHO Director-General announced that production of the unchanged seasonal vaccine should continue for now, and that the WHO would assist the development process for an effective vaccine. U.S.-based medical product company Baxter International has requested a virus sample from the WHO in order to begin development of a new vaccine. Baxter has patented a cell-based technology that may allow the company to develop a vaccine in half the time it usually takes, possibly cutting development time from six months to three.

Of the available antiviral treatments for influenza, the WHO stated that the viruses obtained from the human cases with swine influenza in the United States were sensitive to oseltamivir (Tamiflu) and zanamivir (Relenza) but resistant to amantadine and rimantadine. Tamiflu and Relenza also have a preventative effect against Influenzavirus A. On April 27, the CDC recommended the use of Tamiflu and Relenza for both treatment and prevention of the new strain. Roche and the U.S. government had already extended the shelf life of federally stockpiled Tamiflu from the original five years to seven years because studies indicated that the medication continues to maintain its effectiveness.

Train commuters in Mexico City wearing surgical masks

There is so far little data available on the risk of airborne transmission of this particular virus. Mexican authorities are distributing surgical masks to the general public. The UK Health Protection Agency considers facial masks unnecessary for the general public. Many authorities recommend the use of respirators by health-care workers in the vicinity of pandemic flu patients, in particular during aerosol generating procedures (e.g. intubation, chest physiotherapy, bronchoscopy).

On April 28, the WHO flu expert Keiji Fukuda pointed out that it is too late to contain the swine flu. "Containment is not a feasible operation. Countries should now focus on mitigating the effect of the virus," he said. He also stressed that the experts did not recommend closing borders or restricting travel. "With the virus being widespread... closing borders or restricting travel really has very little effects in stopping the movement of this virus." However, on April 28, the U.S. CDC began "recommending that people avoid non-essential travel to Mexico." The WHO's early reaction was that it saw no need at this point to issue travel advisories warning travelers not to go to parts of Mexico or the United States. The spokesperson said that the situation might change "depending on what the situation in the field is". WHO Director-General Dr. Margaret Chan also said that it was too premature to issue such recommendations without better analysis and understanding of the situation at this stage.

Dr. Ira Longin, a specialist in the mathematical and statistical theory of epidemics, suggests that if those infected stay at home or seek medical care, public meeting places are closed, and anti-flu medications are made widely available, then in simulations the sickness is reduced by nearly two-thirds. "The name of the game is to slow transmission until a well-matched vaccine can be made and distributed. I am fairly optimistic we can do that". In the northern hemisphere the flu season will soon end. However, "Timing is terrible for people in the Southern Hemisphere—places like New Zealand, Australia, South Africa, parts of South America. They are just coming into their flu season."

Cases and responses by nation

  Confirmed deaths  Confirmed cases  Unconfirmed cases
Main article: 2009 swine flu outbreak by country

The new strain has spread widely beyond Mexico, with confirmed cases in ten countries and suspected cases in more than thirty. Many countries have advised their inhabitants not to travel to infected areas. Countries including Australia, China, Iceland, India, Indonesia, Malaysia, Philippines, Singapore, South Korea and Thailand are monitoring visitors returning from flu-affected areas to identify people with fever and respiratory symptoms. Many countries have also issued warnings to visitors of flu-affected areas to contact a doctor immediately if they had flu-like symptoms. Several countries banned import and sale of pork 'as a precaution against swine flu'. Despite no evidence that the virus is present in swine anywhere in the world, Egypt's parliament called for the nation's 250,000 pigs to be killed immediately.

Name of the disease

Some authorities object to calling the flu outbreak "swine flu":

  • U.S. Agriculture Secretary Tom Vilsack expressed concerns that this would lead to the misconception that pork is unsafe for consumption.
  • Israeli deputy health minister Yakov Litzman proposed the name "Mexican flu" because Muslims and Jews consider pork to be unclean, but the Israeli government retracted this proposal following Mexican complaints.
  • The South Korean Ministry for Food, Agriculture, Forestry and Fisheries asked the press to use the term “Mexican Virus” on April 29.
  • Taiwanese authorities suggested the names “H1N1 flu” or “new flu”, which most local media now use.
  • The World Organization for Animal Health has proposed the name "North American influenza".
  • The European Commission uses the term "novel flu virus".

Medical terminology refers to the virus as "Influenza A (H1N1) virus, human". The WHO objects to renaming the disease, because "swine influenza" has been used since the beginning of the outbreak. According to researchers cited by The New York Times, "based on its genetic structure, the new virus is without question a type of swine influenza, derived originally from a strain that lived in pigs".

See also

References

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]

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UN World Health Organization (WHO)
USA Centers for Disease Control (CDC)
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European Centre for Disease Prevention and Control (ECDC)
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