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Revision as of 03:13, 6 May 2009

Template:2009 swine flu outbreak table

The 2009 outbreak of influenza A (H1N1) virus is an epidemic of a new strain of influenza virus that was clinically identified in April 2009,[1] and is commonly referred to as swine flu.[2] It is currently a Phase 5 outbreak, one level below an official pandemic.

Although the exact origin of the outbreak is unknown, it was first detected when officials in Mexico and the United States suspected a link between an outbreak of late-season flu cases in Mexico and cases of influenza in Texas and California.[3] Within days, hundreds more suspected cases were discovered in Mexico, with more cases also showing up in the U.S. and several other countries. By late April, officials from the U.N.'s World Health Organization (WHO), based in Switzerland, and the Centers for Disease Control and Prevention (CDC) in the U.S., were expressing serious concern about the flu outbreak, worried that it might become a worldwide flu pandemic.[4] As a result, WHO raised its alert level to "Phase 5" out of 6 possible, which it defines as a "signal that a pandemic is imminent".[5] By the end of April, 2009 government across the world had taken emergency measures to slow the transmission of a possible pandemic.[6] At the same time, however, many scientists were reaching a consensus that the epidemic was so far "relatively mild," and believed that it could be less fatal than previous pandemics.[7]

The new strain is an apparent reassortment of four strains of influenza A virus subtype H1N1.[8] Analysis by the CDC identified the four component strains as one endemic in humans, one endemic in birds, and two endemic in pigs (swine).[8] However, other scientists have stated that analysis of the 2009 swine flu (A/H1N1) viral genome suggests that all RNA segments are of swine origin.[9] and "this preliminary analysis suggests at least two swine ancestors to the current H1N1, one of them related to the triple reassortant viruses isolated in North America in 1998."[10] One swine strain was widespread in the United States, the other in Eurasia.[8]

Worldwide the common human H1N1 influenza virus affects millions of people every year, according to WHO officials, and "these annual epidemics result in about three to five million cases of severe illness, and about 250,000 to 500,000 deaths" annually.[11] In industrialized countries most of these annual deaths occur in people aged 65 or older.[11] By May 2, some pigs in Canada were diagnosed with H1N1.[12] Although some influenza strains can spread between species, the influenza virus is killed by normal cooking procedures, so there is no risk of infection from consumption of well-cooked pork and pork products.[13]

Historical context

Influenza epidemics historically have occurred every thirty to fifty years.[14] The 1918 flu pandemic infected twenty five percent of the world's population and caused between 20 million and 50 million deaths world wide.[15] The most recent influenza pandemic, the Hong Kong Flu occurred in 1967-1968 and was more mild killing about 700,000 worldwide.[16] Based on the reasoning of a pandemic occurring every thirty to fifty years virologists and public health officials have advised increased preparedness and government plans of actions because according to epidemiologists "it is not a question of if, but when" the next pandemic would arise.[17] The world has been at an increased level of alert since the SARS epidemic in Southeast Asia.[18] This level of preparedness and fear of an outbreak has increased with the advent of the H5N1 bird flu outbreaks because of H5N1's high rate of virulence.

Historical chart

H1N1 influenza virus photographed at the CDC Influenza Laboratory.
Twentieth century flu pandemics
Epidemics (data) Year People infected Deaths Death ratio Data sources
Spanish flu (worldwide) 1918–19 500 million 50 million 10% CDC
Asian flu (U.S.) 1957 45 million 1-4 million Globalsecurity.org
Hong Kong flu (U.S.) 1968–69 50 million 1 million Globalsecurity.org
Seasonal flu (U.S.) yearly average 50 million 0.25-0.5 million 0.07% Globalsecurity.org
Swine flu (worldwide) confirmed
(early phase of epidemic)		 as of May 6, 2009 1767 31 WHO

Initial outbreaks

Further information: 2009 swine flu outbreak timeline

First diagnosis

The new strain of swine flu was first diagnosed as such when the CDC received a sample on April 14 from a patient who fell ill on March 30 in San Diego County, California. A second case was confirmed on April 17 who had fallen ill on March 28 in Imperial County, California.[19][20]

Spread within Mexico

Further information: [[:2009 swine flu outbreak in Mexico]]

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.[21] The surge was assumed by Mexican authorities to be "late-season flu" (which usually coincides with a mild Influenzavirus B peak)[22] until April 21,[23][24] 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.[25] Some samples were sent to the U.S.-based CDC on April 18.[26] The Mexican cases were confirmed by the CDC and the World Health Organization to be a new strain of H1N1.[21][27]

Cases were also reported in the states of San Luis Potosí, Hidalgo, Querétaro and Mexico State.[28] 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."[28] Mexican news media report that the outbreak may have started in February near a Smithfield Foods pig plant amid complaints about its intensive farming practices,[29][30] although no pigs in Mexico have tested positive for the virus.

The first death from swine flu occurred on April 13, when a diabetic woman from Oaxaca died from respiratory complications.[31][32] The Mexican fatalities are alleged to be mainly young adults of 25 to 45, a common trait of pandemic flu.[8][33] Although there have been reports of 152 "probable deaths"[34] in Mexico City and "more than 100 dead from swine flu",[35] the WHO had received reports of only 16 confirmed deaths total and explicitly denied the larger figure as of April 29.[36][37]

Seasonal variation

The high humidity of summer and the increase in exposure to ultraviolet light typically leads to the end of the flu season as the virus becomes less likely to spread.[38] In Mexico City, May marks the end of the dry season, and experts speculate that the spread of the swine flu may slow.[39] On April 30 Mexican Health Secretary Jose Angel Cordova voiced cautious optimism that the spread of the swine flu might be slowing in that country.[40] However, the outbreak comes at the beginning of the flu season for Southern Hemisphere countries such as New Zealand, Australia, South Africa, and parts of South America.[41]

International cases and responses

  Confirmed cases followed by death
  Confirmed cases
  Unconfirmed or suspected cases
See also: H1N1 live map
Main article: 2009 swine flu outbreak by country

The new strain has spread widely beyond Mexico and the U.S., with confirmed cases in eighteen countries and suspected cases in forty-two. Many countries have advised their inhabitants not to travel to infected areas. Areas including Australia, Hong Kong, 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.

Mexico's schools, universities, and all public events will be closed from April 24, 2009 to May 6, 2009.[42][43] By May 3, 2009, more than 400 schools in the U.S. closed due to confirmed or probable cases in students or staff, affecting 250,000 students.[44][45][46][47]

Government actions against pigs and pork

Main article: 2009 swine flu outbreak action against pigs

Although there is no evidence that the virus is transmitted by food,[48] and influenza A viruses are generally killed by heating,[48] some countries banned import and sale of pork products "as a precaution against swine flu".[49][50]

Several countries, including Serbia, China and Russia banned the import of pork products from North America in general as a response to the outbreak, despite assurances from the WHO that the disease is not spread through pork.[51] On April 29, the Egyptian Government decided to kill all 300,000 pigs in Egypt, despite a lack of evidence that the pigs had, or were even suspected of having, the virus.[52] This led to clashes between pig owners and the police in Cairo.[53]

Transmission of flu virus from human to animal

In Alberta, Canada, provincial and federal officials announced on May 2 that a 2,200-head pig herd in central Alberta was under quarantine after preliminary findings indicated some of the animals were infected with swine flu. It is thought that a man who had visited Mexico infected the pigs, in contrast to pigs infecting humans.[54] Alberta agriculture minister George Groeneveld said that health officials expected no problems with export of pork from Canada to the United States, and that there was "absolutely no evidence" that the flu virus can be transmitted through eating pork.[55]

Pandemic concern

See also: Pandemic Severity Index

WHO and CDC officials are concerned that this outbreak may become a pandemic, for the following reasons:[4]

  • New strain
The virus is a new strain of influenza, from which human populations have not been vaccinated or naturally immunized.[56] In the United States, cases infected 25% of family members. Seasonal flu tends to sicken 5% to 20% of family members.[57]
  • 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.[27] The strain was later confirmed to have been transmitted between humans.[58] 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.[citation needed]
  • Virulence
All but two of the fatalities to date have been in Mexico. In Mexico, according to the New York Times, the deaths from the illness have primarily been young, healthy adults.[59] Most other influenza strains produce the worst symptoms in young children, the elderly, and others with weaker immune systems.[27][60] However, the CDC has indicated that symptoms reported from this strain so far are similar to those of normal seasonal flu.[61] While some media outlets have speculated that this virus could cause a cytokine storm in patients,[59] 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."[61]
  • 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. In 1976 the U.S. government incorrectly predicted a swine flu pandemic that never materialized.[62]
WHO officials observed that 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".[27]

By the end of April, however, some scientists believed that this strain was unlikely to cause as many fatalities as earlier pandemics, and may not even be as damaging as a typical flu season.[7]

WHO alert phases

Phase 3

Prior to the swine flu outbreak, the WHO worldwide pandemic alert was set at Phase 3 due to H5N1 avian flu, which spread widely in birds with occasional cases in humans.[64][65][66] 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 WHO decided not to raise the level of the worldwide pandemic alert after its first meeting, on April 25.[66]

Phase 4

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Following the second meeting of the Emergency Committee on April 27, the pandemic alert level was raised to Phase 4.[67] Phase 4, "Sustained Human to Human Transmission," entails community-wide outbreaks.[63]

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

[that the organization was] 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.[68]

Phase 5

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On April 29, the Emergency Committee had their third meeting,[69] and decided to raise the pandemic alert level to five,[5] the second-highest level, indicating that a pandemic is "imminent," and that human-to-human transmission cases have been recorded in multiple countries.[70] In Catalonia, officials confirmed the first European case of an infection in a person who had not (recently) traveled to Mexico, in a person whose girlfriend had done so, the second WHO region to experience intergenerational transmission of H1N1.[71][72]

Media response

The initial outbreak received a week of near constant media attention.[73] The story of the outbreak spread quickly through news networks.[74] Multiple news conferences were aired in the United States by government officials. By the next day, it was the main topic of discussion.[74]

Epidemiologists caution that the number of cases reported in the early days of an outbreak can be very inaccurate and deceptive.[75] This can be due to several causes, including selection bias, media bias, and incorrect reporting by governments.

One hypothetical selection bias in this situation pertains to authorities in different countries looking at different sets of patient populations. For example, doctors in Mexico may be concentrating on patients in hospitals, rather than the larger vulnerable population, which may in part explain the higher mortality recorded in the country.[75] Media bias in reporting swine flu cases and deaths may skew incidence maps based on these media reports. Countries with poor health care systems and poor laboratory facilities may take longer to identify suspected cases, analyse those cases, and report them. Passive data collection methodologies (waiting for the patient to arrive at a health care facility) are considered inferior to active data collection techniques (performing random stratified sampling) because of various forms of selection bias.[76]

Furthermore, if national governments and local health care services for whatever reason do not accurately report their own data on suspected cases and deaths this will produce a garbage in garbage out bias in conclusions drawn from such data by any agency downstream, whether private or governmental, the media or official. For example, World Health Organization accused China of under-reporting cases of SARS during the 2002 SARS outbreak.[77] Gathering accurate data for the flu outbreak is further complicated by the possibility of further mutations of the virus,[78] and because laboratory facilities to perform swift genetic tests on patient samples are not widely available.[75]

Genetics and effects

Template:2009 swine flu genetic table

In this video, Dr. Joe Bresee, with CDC's Influenza Division, describes the symptoms of swine flu and warning signs to look for that indicate the need for urgent medical attention.
See also: See this video with subtitles in YouTube

Genetics

On April 24, the CDC determined that seven samples from suspected cases in Mexico matched the strain that had infected patients in Texas and California with no known linkages to animals or one another; the strain appeared to be spreading from human to human.[4][79] The CDC determined that the strain contained genes 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."[8][80] A CDC investigative team arrived in Mexico City on April 25 to work with Mexican counterparts to study the virus.[23]

Pigs are susceptible to influenza viruses that can also infect both humans and birds, so they may act as a "mixing vessel" in which reassortment can occur between flu viruses of several species.[81][82] Reassortment is a process that happens if two different types of influenza virus infect a single cell and it can produce a new strain of influenza. This is because the virus genome is split between eight independent pieces of RNA, which allows pieces of RNA from different viruses to mix together and form a novel type of virus as new virus particles are being assembled.[83] This new strain appears to be a result of the reassortment of two swine influenza viruses, one from North America and one from Europe.[84] But the North American pig strain was itself the product of previous reassortments, and has carried an avian PB2 gene for at least ten years and a human PB1 gene since 1993.[85] These genes were passed on to the new virus.[86][87]

Gene sequences for every viral gene were made available through the Global Initiative on Sharing Avian Influenza Data (GISAID).[88][89] A preliminary analysis 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. 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.[90] A preliminary analysis has also shown that several of the proteins involved in the pathophysiology of the virus are most similar to strains that cause mild symptoms in humans. This suggests that the virus is unlikely to cause severe infections similar to those caused by the 1918 pandemic flu virus or the H5N1 avian influenza.[91] So far, little is known about the spread of the virus in any pig population. As of April 30 an international team led Juan Lubroth, chief of veterinary investigations for the United Nations Food and Agriculture Organization, in coordination with researchers from the WHO, were in Mexico on the way to La Gloria, in pursuit of what has been dubbed "Pig Zero".[85]

The seasonal influenza strain H1N1 vaccine is thought to be unlikely to provide protection.[92] The virus was also resistant to amantadine and rimantadine, but sensitive to oseltamivir (Tamiflu) and zanamivir (Relenza).[93][94]

Human swine flu symptoms[95]
See also: "Symptoms of swine flu on YouTube". Centers for Disease Control and Prevention.

Symptoms and severity

See also: Swine_influenza#In_humans, for symptoms in previous cases.

The CDC does not fully understand why the U.S. cases' symptoms were primarily mild 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.[96] Differences in the viruses or co-infection are also being considered as possible causes. In 1918, influenza weakened the infected, and it was then lung infections such as pneumonia which killed 3% of them. In the current outbreak, the first deaths (13 and 21 April) were diagnosed as 'atypical pneumonias', a pneumonia which, helped by the flu, becomes more dangerous. The CDC's flu chief Nancy Cox said that genetic analysis of the swine flu strain did not reveal the markers for virulence found in the 1918 flu virus.[97]

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".[98] By April 29, the U.S. had 91 confirmed cases with 5 hospitalizations and one death.[99]

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.[100]

Prevention and treatment

Further information: [[:Influenza: Prevention and Influenza treatment]]

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.[101]

There is no risk of flu transmission from the consumption of properly-cooked pork products.[102]

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.[103] Current development, large-scale manufacturing, distribution and delivery of a new vaccine takes several months.[104][105] 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.[67] 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.[106] Sanofi-Aventis (Sanofi-Pasteur) is manufacturing the conventional seasonal flu vaccine and has not been asked to produce a vaccine against the new H1N1 strain, which would be difficult to manufacture without diverting facilities from current production.[107]

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)[108] and zanamivir (Relenza) but resistant to amantadine and rimantadine.[109] Tamiflu and Relenza also have a preventative effect against Influenzavirus A.[110] On April 27, the CDC recommended the use of Tamiflu and Relenza for both treatment and prevention of the new strain.[111] 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.[112]

Due to a more convenient method of administration, treatment with oseltamivir is typically preferred, but in H3N2 flu treatment leads to resistance in 0.4% of adult cases and 5.5% of children. The resistant strains are typically less transmissible, but that is not certain, and resistant human H1N1 viruses have become widely established. Fortunately, simulations reveal that using a second effective antiviral such as zanamivir (Relenza) to treat even 1% of cases will delay the spread of resistant strains. Even a drug such as amantadine (Symmetrel) for which resistance frequently emerges may be useful in combination therapy.[113][114]

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.[115] 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, Dr. Keiji Fukuda, the Assistant Director-General for Health Security and Environment of WHO, 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.[34] 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."[34] However, on April 28, the U.S. CDC began "recommending that people avoid non-essential travel to Mexico."[116] The WHO's early reaction was that it saw no need at this point to issue travel advisories warning travellers 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".[117] 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.[118] 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.[104] A number of countries advised against travel to known affected regions.

Dr. Ira Longini, 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".[119]

Name of the disease

Scientific name and common name

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".[120] This origin gave rise to the nomenclature "swine flu", largely used by mass media in the first days of the epidemic. Despite this origin, the current strain is now a human-to-human issue, requiring no contact with swine. On April 30 the World Health Organization stated that no pigs in any country had been determined to have the illness, but farmers remain alert due to concerns that infected humans may pass the virus to their herds.[121] On May 2, it was announced that a Canadian farm worker who had traveled to Mexico had transmitted the disease to a herd of pigs, showing that the disease can still move between species.[122]

Debate over name

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.[123] In the Netherlands, it was originally called "pig flu", but is now called "Mexican flu" by the national health institute and in the media. South Korea and Israel briefly considered calling it the "Mexican virus".[124] Currently, the South Korean press uses "SI", short for "swine influenza". Taiwan suggested the names "H1N1 flu" or "new flu", which most local media now use.[125] The World Organization for Animal Health has proposed the name "North American influenza".[126] The European Commission uses the term "novel flu virus".[127]

The WHO announced they would refer to the new influenza virus as influenza A(H1N1) or "Influenza A (H1N1) virus, human"[127] as opposed to "swine flu", also to avoid suggestions that eating pork products carried a risk of infection.[128][129]

Wikinews has related news:

The outbreak has also been called the "H1N1 influenza",[130] "2009 H1N1 flu",[131][132] or "swine-origin influenza".[133] However, Seth Borenstein, writing for the Associated Press quoted several experts who objected to any name change at all.[134]

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See also

External links

Wikimedia Commons has media related to 2009 swine flu outbreak.
Wikinews has related news:
UN World Health Organization (WHO)
USA Centers for Disease Control (CDC)
European Centre for Disease Prevention and Control (ECDC)
Pan-American Health Organization (PAHO)
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