2009 swine flu pandemic

Template:WebSlice-begin Template:2009 swine flu outbreak table Template:WebSlice-end The 2009 swine flu outbreak is the spread of a new strain of H1N1 influenza virus that was first detected by public health agencies in March 2009. Local outbreaks of influenza-like illness were first detected in three areas of Mexico, but the new strain was not clinically ascertained as such until a month later in cases in Texas and California, whereupon its presence was swiftly confirmed in various Mexican states and Mexico City; within days isolated cases elsewhere in Mexico, the U.S., and the Northern Hemisphere were also identified. By April 27, the new strain was confirmed in Canada, Spain, and the United Kingdom and suspected in many other nations, including New Zealand, with over 2,500 candidate cases, prompting the World Health Organization (WHO) to raise their pandemic alert level to 4. A level 4 warning officially means that the WHO considers that there is "sustained human to human transmission"; whereas levels 5 and 6 represent "widespread human infection".

The new strain is an apparent reassortment of several strains of influenza A virus subtype H1N1, including a strain endemic in humans and two strains endemic in pigs, as well as an avian influenza.

In April both the WHO and the United States Centers for Disease Control and Prevention (CDC) expressed serious concerns about the situation. It had the potential to become a flu pandemic because the strain was novel, transmitted from human to human against little immunity, and the Mexican mortality rate was unusually high. On April 25, 2009, the WHO determined the situation to be a formal "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.

As of April 26, 2009, Mexico City schools, universities, and all public events remained closed or suspended while other schools in the U.S. closed due to confirmed cases in students. On April 27, 2009, Mexican government officials announced a nationwide shut down of schools.

Prior influenza season

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 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 improvement was also attributed to new recommendations 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 outbreak

  Confirmed cases followed by death

  Confirmed cases

  Unconfirmed or suspected cases

See also: Live map of swineflu, H1N1 live map

The earliest confirmed case of the illness was in the town of La Gloria near Perote, Mexico, where a boy fell ill on April 2. 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 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, causing 152 deaths (26 confirmed) so far, mostly in Mexico City. There have also been cases reported in the states of San Luis Potosí, Hidalgo, Querétaro and Mexico State, all in central Mexico; Some cases in Mexico and the United States have been confirmed by the World Health Organization to be a never-before-seen strain of H1N1. The Mexican fatalities are mainly young adults of 25 to 45, a hallmark of pandemic flu. A new swine flu strain was confirmed in 16 of the deaths and at least 100 others were being tested as of April 24, 2009. 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

The CDC has confirmed that American 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 reassortment of human influenza and swine influenza viruses, presumably due to superinfection in an individual human. 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).

Several complete genome sequences for U.S. flu cases were rapidly made available through the Global Initiative on Sharing Avian Influenza Data (GISAID). 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.

Main symptoms of swine flu in humans.

The CDC does not understand why the American cases were primarily mild disease while the Mexican cases had led to multiple deaths. However, research on previous pandemic strains have 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. Only fourteen samples from Mexico had been tested by the CDC, with seven 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. While the seasonal flu kills less than 1% of those infected, the Mexican fatality rate represents a 7% rate. This compares to the global rate of more than 2.5% for the Spanish flu pandemic of 1918.

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."

Unlike what usually happens in cases of influenza, which inflict a greater number of deaths between the elderly and the children, this strain resulted in deaths only in people between the ages of 25 and 50.

Pandemic concern

See also: Pandemic Severity Index

The U.S. Centers for Disease Control (CDC) and the World Health Organization (WHO) 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 appeared to infect 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

The virus has produced severe disease in Mexico, and some deaths. Furthermore, in Mexico (but not in the United States) the illness has primarily struck young, healthy adults, much like the deadly Spanish Flu of 1918, possibly because of the phenomenon known as cytokine storm. Most other influenza strains produce the worst symptoms in young children, elderly adults, and others with weaker immune systems.

Lack of data

That other factors are still somewhat unknown, such as transmission rates and patterns and effectiveness of current influenza treatments, combined with the 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.

Prevention and treatment

Train commuters in Mexico City wearing surgical masks.

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. People should avoid touching their mouth, nose or eyes with their hands unless they've washed their hands. If people do cough, they should either cough into a tissue and throw it in the garbage immediately or, if they cough in their hand, they should wash their hands immediately.

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 look 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.

To maintain a secure household during a pandemic flu, the Water Quality & Health Council recommends keeping as supplies food and bottled water, portable power sources and chlorine bleach as an emergency water purifier and surface sanitizer.

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. 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 remantadine. 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 US government had already extended the shelf-life of federally stock-piled Tamiflu from the original five years to seven years because studies indicated that the medication continues to maintain its effectiveness.

Some physicians in the US are recommending the use of masks when in public. The purpose of a face mask is to effectively cover a person's mouth and nose so that if a person is around someone who is infected, there is a decreased likelihood of transmission. Recommendations to protect against the avian flu indicated that using a face mask with a rating of N99, N100 or P100 in the United States or a rating of FFP3 in Europe should be effective in protecting against transmission. While face masks with these ratings provide 99% or greater efficiency in protecting against flu transmission, N95 or FFP2 face masks provide about 94% efficiency. N95 and FFP2 rated face masks may therefore also be effective.

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."

UN World Health Organization

Congruent WHO and U.S. Government Pandemic Response Charts

The World Health Organization (WHO) 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". 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.

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" and "WHO acknowledges the United States and Mexico for their proactive reporting and their collaboration with WHO and will continue to work with Member States to further characterize the outbreak".

The WHO established the Emergency Committee of the International Health Regulations for emergency discussions to assess the situation and to formulate appropriate responses, and to provide guidance and advice to the Director-General. The first meeting of the committee was held on April 25 in Geneva.

Before the first meeting, WHO Director-General Margaret Chan said that the Emergency Committee could make recommendations including whether to change the pandemic alert level or not.

The Emergency Committee "identified a number of gaps in knowledge about the clinical features, epidemiology, and virology of reported cases and the appropriate responses", and on its advice, the WHO advised "that all countries intensify surveillance for unusual outbreaks of influenza-like illness and severe pneumonia".

The WHO decided not to raise the level of the worldwide pandemic alert after the first meeting. 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, "Sustained Human to Human Transmission," entails community-wide outbreaks; Phases 5/6, "Widespread Human Infection," entails human-to-human transmission in at least two countries in one WHO region; Phase 6 is a global pandemic proper.) Following the second meeting of the Emergency Committee on April 27, 2009, the WHO raised the pandemic alert level to 4.

Cases and responses by nation

Main article: 2009 swine flu outbreak the international response

There has been a wide spread international response.

See also

• 2009 swine flu outbreak timeline
• Swine influenza
• Spanish flu
• Hong Kong Flu (1968–1969) killed an estimated one million people worldwide
• Severe acute respiratory syndrome (SARS)
• Health care in Mexico

External links

• Swine Flu Report in China 20090428
• Global map of reported H1N1 outbreaks in 2009
• H1N1 outbreak timeline
• Swine Flu Outbreak, Influenza Virus Resource — sequences and related resources (GenBank, NCBI)
• BioHealthBase Bioinformatics Resource Center Database of influenza genomic sequences and related information.
• SwineFlu Live Updated IRC channel

UN World Health Organization (WHO)

• Swine influenza, at the World Health Organization
• WHO's current Pandemic Influenza Phase
• @whonews twitter account

USA Centers for Disease Control (CDC)

• Swine Influenza (Flu) portal
  • Human Swine Influenza Investigation
  • Interim Guidance on Case Definitions for Swine Influenza A (H1N1) Human Case Investigations for state and local health department investigations, defines confirmed, probable and suspected
  • RSS feed
• Video podcast
• @CDCemergency twitter account

European Centre for Disease Prevention and Control (ECDC)

• Threat Assessment for Swine Influenza at 19:00 hours 24 April 09
• Information with Daily Update
  • Swine Influenza FAQs
  • ECDC Pandemic Preparedness Report