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The 2009 H1N1 influenza outbreak is the spread of a new strain of influenza virus that began in March of 2009. Localized outbreaks of influenza-like illness (ILI) were detected in three areas in Mexico and two in the United States. Following the discovery of the new strain in the United States, its presence was quickly confirmed in three of those areas: in Mexico City, California, and Texas. There have been over 1,000 suspected cases. Because it is not possible to confirm every one of such cases as being caused by an influenza virus, the World Health Organization (WHO) refers to them collectively as influenza-like illnesses (ILI). The cases are characterized by severe influenza-like symptoms, followed by pneumonia, which has been fatal in some Mexican cases. The new strain is derived in part from human influenzavirus A (subtype H1N1), and in part from several strains of influenza virus usually found only in swine (see Swine flu). In April both the WHO and the U.S. Centers for Disease Control (CDC) expressed serious concerns about this novel strain, because it apparently transmits from human to human, has had a relatively high mortality rate in Mexico, and because it has the potential to become a flu pandemic.

On April 25, 2009, 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, including the European Centre for Disease Prevention and Control (ECDC), the UK Health Protection Agency, US Centers for Disease Control and Prevention (CDC), and the Public Health Agency of Canada, have also expressed concerns over the outbreak and are monitoring the situation closely.

Background of outbreak

Prior influenza season

Prior to the outbreak, the winter of 2008-2009 had been a comparatively mild season for flu infections, which typically cause 250,000-500,000 deaths yearly, mostly in the elderly, the very young, and persons with chronic illness. Up to April 8, 2009, the CDC (Centers for Diseases Control) 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 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 5-18 year olds, who potentially act as "super-spreaders" due to failure to take precautions such as hand-washing.

Furthermore, from December 2005 through February 2009, a total of twelve human infections with swine influenza were reported from ten states in the U.S.A.

New influenza outbreak

The outbreak was first detected in the Federal District of Mexico, where surveillance began picking up cases of ILI starting 18 March. But days or weeks were lost as the cases were initially assumed to be a "late-season flu" by Mexican authorities until as late as April 21. 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. A CDC alert concerning these two isolated cases was reported in the media on April 21. The story of the outbreak was broadcast live first in Mexico on April 23, 2009.

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 was unusually virulent in Mexico, causing 81 confirmed deaths so far, mostly in Mexico City, but there have been reported cases 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 has been confirmed in 16 of the deaths and at least 100 others are 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

Influenza (flu)
Types Avian A/H5N1 subtype Canine Equine Swine A/H1N1 subtype
Vaccines 2009 pandemic Pandemrix Live attenuated Seasonal flu vaccine brands
Treatment Amantadine Baloxavir marboxil Laninamivir Oseltamivir Peramivir Rimantadine Umifenovir Zanamivir
Pandemics 1889-1890 Russian flu 1918 Spanish flu 1957-1958 Asian flu 1968 Hong Kong flu 1977 Russian flu 2009 swine flu
Outbreaks 1976 swine flu 2006 H5N1 India 2007 Australian equine 2007 Bernard Matthews H5N1 2008 West Bengal 2015 United States H5N2 outbreak 2020–2022 H5N8 outbreak
See also Flu season Influenza evolution Influenza research Influenza-like illness Vaccine reformulations
v t e

Anne Schuchat, director of CDC's National Center for Immunization and Respiratory Diseases, said that the 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 A virus subtype H1N1, and swine influenza virus typically found in Asia and Europe - "an unusually mongrelised mix of genetic sequences." 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 packaged in 8 pieces (see Orthomyxoviridae).

For two cases a complete genome sequence had been obtained. This complete genome is presently being worked with by U.S. scientists to prepare it for transition to become a vaccine. Director Schuchat said that the virus was resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).

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. 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.

In an interview on April 24, acting CDC director Richard Bessar said that it was still not understood why the American cases were primarily mild disease while the Mexican cases had led to multiple deaths. Differences in the viruses or co-infection were being considered. Only fourteen samples from Mexico had been tested by the CDC, with seven found to match the American strain. He said that the virus had likely passed 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 had arrived in Mexico city on April 25 to work with Mexican counterparts to study the virus.

According to Mike Stobbe of the Associated Press:

A big question is: Just how deadly is the virus in Mexico?

The seasonal flu tends to kill just a fraction of 1 percent of those infected.

In Mexico, about 70 deaths out of roughly 1,000 cases represents a fatality rate of about 7 percent. The Spanish flu pandemic of 1918-19, which killed an estimated 50 million worldwide, had a fatality rate of about 2.5 percent.

The Mexican rate sounds terrifying. But it’s possible that far more than 1,000 people have been infected with the virus and that many had few if any symptoms, said Dr. Michael Osterholm, a prominent pandemic expert at the University of Minnesota. U.S. health officials echoed him.

Confirmed cases

Mexico

Mexican officials stated that since March 2009, there have been over 1300 reported cases and put the death toll at 83, with 20 confirmed to be linked to a new swine influenza strain of Influenza A virus subtype H1N1.

United States

Officials in the United States confirmed that seven people in California, two students from a high school in Texas, and a married couple in Kansas were infected with the A/09(H1N1) swine flu; all have recovered. One additional student from the same high school in Texas is suspected of probably having the influenza strain. New York now has confirmed cases of swine flu. The cases in Kansas and New York are linked to travel to Mexico; most of the cases in California and Texas are not linked and may reflect localized outbreaks of this virus in those areas. One case has been confirmed in Ohio. A public health emergency has been declared, but it was said that this is standard procedure in cases as divergent as the recent inauguration and flooding.

Canada

Pandemic concern

The U.S. Centers for Disease Control and the World Health Organization are concerned that this outbreak may become a pandemic, because:

New strain

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

Human transmission

The virus appears to infect by human-to-human transmission. Investigations of infected patients indicate no direct contact with swine, such as at a farm or agricultural fair. 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. Most other influenza strains produce the worst symptoms in young children, elderly adults, and others with weaker immune systems.

Geography

The virus has been detected in multiple regions within Mexico and multiple areas in the United States.

Prevention and treatment

Recommendations to prevent infection by the virus consist of the standard personal precautions against influenza.

The previously recommended influenza vaccines for the southern and northern hemisphere, including that for the 2009/2010 flu season, are ineffective against the new strain. The development, large-scale manufacturing, distribution and delivery of a new vaccine takes a number of months.

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.

UN World Health Organization

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 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 an Emergency Committee for emergency discussions to assess the situation and to formulate appropriate responses. The first meeting of the committee was held on 25 April 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 WHO decided not to raise the level of the worldwide pandemic alert after the first meeting, which remains at Phase 3 out of the six-point scale. A Phase 3 alert means that a new virus has been confirmed but there is no or limited evidence of human to human transmission and is insufficient to sustain community-level outbreaks. The Phase 3 alert was set due to the avian flu.

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".

National responses

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. In the USA, two confirmed cases were detected through their "border infectious disease surveillance".

Canada

Dr. Michael Gardam, director of infectious disease prevention and control at Ontario's public health agency, said in an interview with the CBC that an outbreak of swine flu in Ontario, Canada's most populous province, would not be as serious as the 2003 SARS epidemic. In preparing for and dealing with an influenza pandemic, the Public Health Agency of Canada follows the WHO's categories, but has expanded them somewhat. Despite initial reports of two swine influenza cases in a Montreal hospital, an official on the Montreal regional health board confirmed negative results for all quarantined patients at the hospital and that no quarantines were currently in effect at the hospital. On April 26, the Government of Nova Scotia announced, on a live webcast, that four students attending King's-Edgehill School in Windsor, Nova Scotia have confirmed cases of swine flu.

Canadian laboratories assisted the Mexican government in confirming their eighteen confirmed cases.

Chile

The Health Ministry reported that three people suspected of being infected with swine flu are under observation in the Coyhaique Regional Hospital, the Carlos Van Buren Hospital in Valparaíso and the Hospital del Tórax in Santiago. The Health minister Alvaro Erazo stated that two of the cases have initially tested negative to exams, indicating they are likely not infected, while a third case is under study. Regarding the Chivas de Guadalajara football team, slated to arrive to Chile from Mexico, the minister stated they will undergo examination as will other passengers.

China

China's General Administration of Quality Supervision, Inspection and Quarantine (GAQSIQ) announced that visitors returning from flu-affected areas who experienced flu-like symptoms within two weeks would be quarantined. Hong Kong and Taiwan said that visitors returning from these areas with fevers would be quarantined. Hong Kong warned against travel to Mexico City and three Mexican states.

The Ministry of Health has started prevention measures and initiated contact with the World Health Organization (WHO) and the relevant departments of the governments of Mexico and the U.S. to contain the outbreak.

France

In France, possible cases of swine flu were being investigated in four people who had recently visited Mexico. Other tested cases had proved negative.

Indonesia

Indonesia increased surveillance for passengers with flu-like symptoms at all entry points, using devices at airports previously installed to monitor passenger temperatures to prevent the spread of SARS or avian influenza. Officials said that they were ready to quarantine suspected cases if necessary.

Japan

The Japanese Ministry of Foreign Affairs has issued a warning to urge those who are planning to travel to Mexico to consider aborting their trips. Tokyo's Narita Airport installed a device to measure the temperatures of passengers arriving from Mexico.

The Ministry of Agriculture, Forestry and Fisheries instructed animal quarantine offices across Japan to examine any live pigs to be brought into Japan to make sure they are not infected with the influenza. Japanese Agriculture Minister Shigeru Ishiba appeared on television to reassure customers that it was safe to eat pork. The Japanese farm ministry said that it would not ask for restrictions on pork imports because the virus was unlikely to turn up in pork, and would be killed by cooking.

Mexico

On April 24, 2009, schools (from pre-school to university level) as well as libraries, museums, concerts and any public gathering place, were shut down by the government in Mexico City and the neighbouring State of Mexico to prevent the disease from spreading further; the schools in Mexico City, the State of Mexico, and the state of San Luis Potosí will remain closed through at least 5 May. Marcelo Ebrard, Mexico City's mayor, has also asked all night-life operators to shut down their places for ten days to prevent further infections. José Ángel Córdova, federal Secretary of Health, said on April 24 that schools will probably be suspended for at least the following week then, and that it will take around ten days to see the evolution of the virus' behavior, and to consider other measures after such. On April 25, President Felipe Calderón declared an emergency which granted him the power to suspend public events and order quarantines. Hours later, Córdova announced classes will be officially suspended through May 6.

Netherlands

The Netherlands National Institute for Public Health and the Environment advised any traveller who returned from Mexico since April 17 and developed a fever of 38.5 degrees Celsius (101.3 degrees Fahrenheit) within four days of arriving in the Netherlands to stay at home.

New Zealand

Following a three-week language trip to Mexico, ten students from Rangitoto College, a secondary school in North Shore City, Auckland, exhibited influenza symptoms. All 22 students and three accompanying teachers from the trip are currently in home isolation, with oseltamivir provided to the patients and those in contact with them. 10 students have tested positive for an influenza A virus; further testing is needed to confirm A/09 (H1N1) infection.

Peru

In response to the outbreak, Alex Kouri, governor of Callao, announced that the Callao Regional Government took precautionary steps to prevent entry of the virus by declaring a state of maximum air and sea alert. Callao has Peru's largest sea and air ports. Peru's health ministry said that authorities will monitor travellers from the U.S. and Mexico, and those with flu-like symptoms will be evaluated by health teams.

Philippines

Health Secretary Francisco T. Duque III has ordered the Bureau of Quarantine to use thermal imaging equipment at airports to screen passengers coming from the US for flu symptoms. The Philippines may quarantine travelers arriving from Mexico with fevers. Also, the Secretary of the Department of Agriculture of the Philippines issued an order banning the importation of hogs from the U.S. and Mexico, and the retraction of the restriction of swine influenza vaccine use.

Poland

The Polish Foreign Ministry issued a statement recommending that citizens avoid travel to affected areas until the outbreak is totally contained.

Russia

A Russian health agency said that any passenger from North America running a fever would be quarantined until the cause of that fever was determined.

Russian Agricultural Control Agency (Rosselkhoznadzor) banned all imports of pork from Mexico, several southern USA states (Texas, California, Arizona, Arkansas, Georgia, Louisiane, New Mexico, Oklakhoma, Florida, and Kansas), and from 9 countries of Latin America (Guatemala, Honduras, Dominician Republic, Columbia, Costa Rica, Cuba, Nicaragua, Panama, Salvador)

Serbia

On April 25 Serbia banned all imports of pork from North America.

Singapore

Singapore's Minister of Health Khaw Boon Wan has urged citizens to limit travel to affected areas such as Mexico and the United States. The Health Ministry has advised the public to seek immediate medical attention if they experience influenza symptoms within seven days after arriving from affected areas, to maintain good hygiene, and for those who are sick with respiratory illnesses to avoid crowded areas and wear masks.

South Korea

South Korea warned against travel to Mexico City and three Mexican states.

Spain

AENA, the Spanish state owned company who manages all Spanish airports and Air Traffic Control established a protocol for the flights coming from and to Spain from the affected areas.

Three patients who had just returned from Mexico were under observation in in multiple regions of Spain.

United Kingdom

On April 25, 2009, a British Airways member of the cabin crew of British Airways flight number BA242 was taken to hospital and quarantined after falling ill with "flu-like symptoms" on a flight from Mexico City to Heathrow. The man, who was not named, was taken to Northwick Park Hospital in Harrow for further testing and treatment under quarantine. On April 26, Northwick Park Hospital said that the crew member did not have the swine flu.

Two people were hospitalized in Scotland with mild flu-like symptoms after returning from Mexico, although the Scottish Health Secretary said they were not giving cause for concern. The UK Government has now announced that they are doing on-board inspections of all passengers arriving from Mexico.

See also

• 1918 flu pandemic
• Avian flu
• Hong Kong Flu (1968-1969) Last major pandemic, which killed an estimated one million people worldwide.
• Infectious disease
• Pandemic Severity Index
• Severe acute respiratory syndrome (SARS)
• Swine influenza 1976 U.S. outbreak
• Virulence

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External links

• Swine influenza, at the World Health Organization
• BioHealthBase Bioinformatics Resource Center Database of influenza genomic sequences and related information.
• Global map of reported H1N1 outbreaks in 2009

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
  • RSS feed
• Video podcast
• @CDCemergency twitter account

European Centre for Disease Prevention and Control (ECDC)

• Threat Assessment for Swine Influenza at 19:00 hours 24th April 09
• Information with Daily Update
  • Swine Influenza FAQs

• Current events from April 2009
• 2009 in Mexico
• 2009 in the United States
• Health in Mexico
• Influenza A virus subtype H1N1
• Medical disasters
• Disease