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2009 swine flu pandemic

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The outbreak of a new strain of influenza virus in March and April of 2009 is infecting many people in Mexico City, other regions of Mexico, and parts of the United States. It can cause severe influenza-like illness, followed by pneumonia, which has, in some Mexican cases, resulted in death. 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 World Health Organization (WHO) and the U.S. Centers for Disease Control (CDC)[1] expressed serious concerns that this novel strain because it apparently transmits from human to human, has had a relatively high mortality rate in Mexico, and 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".[2] Government health agencies around the world, including the European Centre for Disease Prevention and Control (ECDC), the UK Health Protection Agency and the Public Health Agency of Canada, have also expressed concerns over the outbreak and are monitoring the situation closely.

Cases of this strain of influenza by country or state.
Country or State Confirmed laboratory cases Other possible cases* Deaths from all cases*
Mexico 18[3] 1300+[4] 81[5]
California 7[6] 0 0
Texas 2[6] 1[7] 0
Kansas 2[6] 0 0
New York 0[8] 8[8] 0
New Zealand 13 25+[9] 0
Total 29 1300+ 81
(*) Not all cases have been confirmed as due to this strain. Possible cases are cases of influenza-like illness (ILI) that have not been confirmed through testing to be due to this strain.

Background of outbreak

Train commuters in Mexico City wearing surgical masks.

Prior to the outbreak, the winter of 2008-2009 was a comparatively mild year for flu infections, which typically cause 36,000 deaths 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 2008 seasonal flu vaccine, in which a rare decision was made to update all three strains (H1, H3, and B) simultaneously, ultimately yielding a very good match to circulating strains of H1N1 and H3N2. This followed the poor performance of the 2007 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.[10][11]

From December 2005 through February 2009, a total of 12 human infections with swine influenza were reported from ten states in the USA.[12]

The outbreak was first detected in the Federal District of Mexico, where surveillance began picking up cases of ILI starting 18 March.[13] 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.[14] The first two cases identified as swine flu were two children living in San Diego County and Imperial County, California, who became ill on March 28 and 30.[15] A CDC alert concerning these two isolated cases was reported in the media on April 21.[16] The story of the outbreak was broadcast live first in Mexico on April 23, 2009.

Mexican soldier giving surgical mask to the population

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;[4] In the United States, virulence apparently was below average. 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.[13][3] The Mexican fatalities are mainly young adults of 25 to 45, a hallmark of pandemic flu.[17][18] 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.[19] Mexican Health Minister José Ángel Córdoba on April 24, said "We’re dealing with a new flu virus that constitutes a respiratory epidemic that so far is controllable."[4]

Genetics and effects

Influenza (flu)
H1N1 virus
Types
Vaccines
Treatment
Pandemics
Outbreaks
See also

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."[20] 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. She said that the virus was resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).[21][22][23][24]

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.[25] The seasonal influenza strain H1N1 vaccine is thought to be unlikely to provide protection.[26]

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".[27][28] 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.[14]

Countries affected

Mexico

Mexican officials state that since March 2009, there have been over 1300 reported cases[29] 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.[30][31][32]

United States

Main article: 2009 H1N1 flu outbreak in the United States

Officials in the United States have 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.[33] One additional student from the same high school in Texas and eight students from a private school in New York City are suspected of probably having the influenza strain.

Pandemic concern

The U.S. Centers for Disease Control and the World Health Organization are concerned that this outbreak may become a pandemic, because:[34]

  • The virus is a new strain of influenza, from which human populations have not been vaccinated or naturally immunized.[35]
  • 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. This is unlike most influenza strains which produce the worst symptoms in young children, elderly adults, and others with weaker immune systems.[36][3]
  • 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.[3] 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.[37]
  • The virus has been detected in multiple regions within Mexico and multiple areas in the United States.

National responses

Argentina

Argentina declared a health alert, requiring anyone arriving on flights from Mexico to advise if they had flu-like symptoms.[38]

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.[39] In preparing for and dealing with influenza pandemic, the Public Health Agency of Canada follows the WHO's categories, but has expanded them somewhat.[40] 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.[41] Students in Nova Scotia are currently being tested for swine flu; if the tests return positive, they would be the first confirmed Canadian cases. [42]

Canadian laboratories assisted the Mexican government in confirming their eighteen confirmed cases.[3]

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.[43]

Hong Kong

The Centre for Health Protection has boosted local surveillance systems due to the outbreaks of swine influenza in Mexico and the United States. The controller of the Centre Thomas Tsang said surveillance at boundary control points and at the public health laboratory will be enhanced. Travellers from affected areas who are found to have symptoms of swine influenza will be hospitalized for laboratory testings and further investigations. The Government has also issued reminders to travellers who are planning to travel to the affected places to consider the latest development of the situation.[44]

Japan

The Japanese Government has stepped up health check procedures of passengers arriving in the country. The Ministry of Foreign Affairs has issued a warning to urge those who are planning to travel to Mexico to consider aborting their trips. 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. [45]

Mexico

Mexican soldiers distributing protective masks to citizens.

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.[46] 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.[47] José Ángel Córdoba, 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.[48] On April 25, President Felipe Calderón declared an emergency which granted him the power to suspend public events and order quarantines.[49] Hours later, Córdoba announced classes will be officially suspended through May 6. [50]

New Zealand

Following a three-week language trip to Mexico, six 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 until preliminary results from an influenza test are known on Monday.[51][9]

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.[52] Callao has Peru's largest sea and air ports.

Philippines

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.[53]

United Kingdom

The Health Protection Agency said on 24 April: "No cases of swine flu have been identified in the UK or anywhere in Europe. The reported events in the US and Mexico are unusual and warrant further investigation and vigilance on the part of other countries. More investigation and testing is needed to determine the severity of the disease and the ease with which it can spread."[54]

On 25 April 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.[55] The man, who was not named, was taken to Northwick Park Hospital in Harrow for further testing and treatment under quarantine. On April 26th, Northwick Park Hospital said that the crew member did not have the swine flu. [56]

United States

An official for the White House said, "The White House is taking the situation seriously and monitoring for any new developments. The president has been fully briefed."[57] Gov. Arnold Schwarzenegger and the state of California activated the Joint Emergency Operations Center of the Department of Public Health, and are coordinating with the California Emergency Management Agency, the CDC, and the Mexican government. They have additionally stepped up other preparations to lessen the flu's threat.[58]

The CDC has been distributing information to the public via press conferences, television appearances, its Swine Flu website pages (half a million visits on April 24 and a million on April 25), an RSS feed ([1]), a video podcast ([2]), and the twitter account @CDCemergency.[59][60][61] It also held a conference call for clinicians on April 25 and issued a health advisory afterwards.[62][12] An "Interim Guidance on Case Definitions" was issued on April 24 for state and local health department investigations.[63]

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".[64] 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.[65]

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".[3]

The WHO stated that the viruses obtained from the human cases with swine influenza in the United States were sensitive to oseltamivir (Tamiflu)[66] and zanamivir (Relenza) but resistant to amantadine and remantadine. [67]

The WHO has 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.[2]

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.[64][68]

The WHO chose not to raise the level of the worldwide pandemic alert to Phase 3 out of the six-point scale, meaning a new virus has been confirmed but there is no or limited evidence of human to human transmission. The Phase 3 alert was set due to the avian flu.[69][70][71]

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".[2]

See also

References

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  2. ^ a b c "Statement by WHO Director-General, Dr Margaret Chan 25 April 2009 — Swine influenza". World Health Organization. 2009-04-25. Retrieved 2009-04-26.
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  37. ^ Global spread of H5N1
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  54. ^ Health Protection Agency
  55. ^ Cabin crew member in hospital after flight from swine flu-struck Mexico
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