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The Epidemic of Influenza Virus a (h1n1) Infection

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H1N1 Swine flu is a subtype of the influenza A virus, which differs from other strains (H1N1, H1N2) in the surface glycoproteins hemagglutinin and Neuraminidase. Primarily, it is thought to have the spread of this novel virus through respiratory droplets; Coughing, Sneezing, touching respiratory droplets yourself, another person, or an object, then touching mucus membranes (e.g.., mouth, nose, eyes) without washing hands. Once the infection occurs, the clinical spectrum of the infection ranges from mild upper respiratory tract illness to severe complications such as pneumonia resulting in respiratory failure, acute respiratory distress syndrome (ARDS), multi-organ failure, and death. This novel H1N1 virus was first reported in 2009 in Mexico then WHO officially declared the start of the 2009 influenza pandemic in June 2009. The magnitude of this pandemic was tremendous. It did not only affect the community’s health and healthcare but also affected other economic and social aspects. There are various measures for the prevention and control of H1N1 infection have been implemented including non-pharmacological and pharmacological interventions. Due to the explosive demands for extensive studies of this novel virus, this paper points out the magnitude of the problem, potential of transmission, and predisposing factors. Moreover, it explores the various dimensions of clinical presentation, prevention, and control.


H1N1 swine influenza is a widespread infection in pigs worldwide and is also known as swine flu for this reason.  H1N1 swine flu contributes to respiratory illness and can theoretically affect the pig’s breathing tract. Occasionally people who are closely related to pigs or close to pigs develop swine flu (zoonotic swine flu). Swine influenza viruses can potentially cause human infections if the virus changes its antigenic characteristics by reassortment.

Influenza A pandemics such as those which occurred in 1918 and 2009 can occur when transmission from person to person becomes successful. In 1918, a devastating influenza pandemic caused by the H1N1 influenza virus, also known as Spanish flu, marked it as one of human history’s most lethal pandemics.

In 2009, the outbreak of swine-human influenza (H1N1), which is likely to spread from pigs to humans, began in Mexico and spread quickly to many countries across the world. This new ‘pandemic’ was attributed to a three-fold influenza A virus-carrying of swine gene, Eurasian avian, and human strains, though it is unclear when and where reassortment occurred.

Causative Agent:

The H1N1 influenza virus is an orthomyxovirus, developing virions with an RNA genome of 80 to 120 nm in diameter the swine influenza genome has 8 different regions which are segmented and encode 11 different proteins:

  • · Envelope proteins hemagglutinin (HA) and neuraminidase (NA)
  • · Viral RNA polymerases which include PB2, PB1, PB1-F2, PA, and PB
  • · Matrix proteins M1 and M2
  • · Nonstructural proteins NS1 and NS2 (NEP), which are crucial for efficient pathogenesis and viral replication.

HA and NA surface glycoproteins are how H1N1strain varies from another influenza A strains (H1N1, H1N2) depending on the type of HA or NA antigens expressed with metabolic synergy. Hemagglutinin has the function of causing red blood cells to bind together, and binding the virus to the infected cell. Neuraminidase helps to transfer particles of the virus across infected cells.

The magnitude of the problem:

H1N1 influenza was first reported in Mexico on the 18th of March In 2009. Within weeks, the epidemic spread through 30 countries. By June 11, the WHO officially declared the start of the 2009 influenza pandemic by signaling the phase 6 alert level as nearly 30,000 cases of the 2009 H1N1 virus had been confirmed across 74 countries.

The infection was recorded in 122 countries by July, with 134,000 laboratory-confirmed cases and 800 deaths. The scale of global trade and travel has enabled the outbreak of swine flu in six weeks to the same degree as previous pandemics in six months. By December 2009, more than 208 countries and territories had reported swine flu cases. As of March 2010, almost all countries registered cases, and more than 17,700 deaths among laboratory-confirmed cases. In the United States, an estimated 59 million illnesses, 265,000 hospitalizations, and 12,000 deaths had been caused by the 2009 H1N1 virus as of mid-February 2010. It is important to note that the mortality estimation may have been underestimated as it relied on statistical attribution of excess all-cause mortality rather than laboratory-confirmed cases.

According to the Ministry of Health, the number of laboratory-confirmed cases in Saudi Arabia as of 30 December 2009 was 15,850, with 124 deaths. Apart from the pandemic’s medical impact, it was also the cause of the societal disruption. It negatively affected global tourism, with airlines reporting losses in the tens of millions. In Mexico, international air traffic to/from the country declined by 40% following the travel-related controls of some countries during the early stages of the outbreak in an attempt to contain or slow down its international spread. Moreover, the closing of schools in the United States for an average of four weeks had cost up to 47 billion dollars (0.3% of GDP) with a reduction of 19% in key healthcare workers.

Predisposing factors:

Overall People who have a higher risk of being infected with this virus include:

  • · Children younger than 5 years old.
  • · Adults older than age 65, younger adults, and children under age 19 who are on long-term aspirin therapy.
  • · People with compromised immune systems due to diseases such as AIDS.
  • · Currently gestating females.
  • · People suffering from chronic diseases such as asthma, heart disease, diabetes mellitus, or neuromuscular diseases.


The potential mode of transmission is through droplets by either coughing or sneezing and direct or indirect contact with an infected person’s respiratory secretions. Handling virus-contaminated surfaces (fomites) as well as inhalation of bacterial aerosols to the nose or mouth. Fomites are inanimate objects (e.g. Children’s toys) which by indirect contact can serve as vehicles for the spread of the disease. Infectious aerosols are composed of large droplets and droplet nuclei. Large respiratory droplets have a diameter of >5–10 μm and are involved in short-range transmission. The diameter of the droplet’s nuclei is < 5 μm and it is responsible for long-distance transmission (long-range or airborne transmission). The rapid spread was observed amongst the population, especially in crowded places such as schools.

Clinical Presentation: 

Symptoms of (H1N1) are similar to those with seasonal influenza: fever, cough, sore throat, malaise, headache, myalgia, arthralgia, and fatigue. Many patients, especially in the pediatric age group, presented with vomiting and diarrhea, which are not commonly seen with seasonal influenza. The available data suggest that the clinical range of H1N1 virus infection is wide, ranging from mild upper respiratory tract disease to serious complications such as respiratory failure, acute respiratory distress syndrome (ARDS), multi-organ failure, and death. Gastrointestinal symptoms such as diarrhea have been reported in 20%–50% of patients, and do not require hospitalization. For certain countries, primary viral pneumonia or viral pneumonitis is the key cause for hospitalization. Microbiological evidence of secondary bacterial or fungal infection has been found in fatal events… In the USA, >70% of hospitalized patients and approximately 80% of fatal cases have had underlying conditions considered to put them at high risk for complications.

Surveillance data on hospitalizations and deaths from H1N1 infection show that individuals who are pregnant, at extremes of age, and who have underlying chronic diseases are most at risk for severe or complicated influenza illness. An additional risk factor that has become apparent with this pandemic influenza is obesity (body mass index, Q30 kg/m2), a feature that has not been prevalent in previous seasonal influenza epidemics.

Similarly, information on the incubation period of this virus has been inferred from that of seasonal influenza and ranges from 1 to 7 days. Children who are ill with an ILI are presumed to shed the virus from the day preceding fever until up to 7 days after illness onset; viral shedding may be longer in certain groups such as young infants and immunocompromised children. For prophylaxis, the infectious period for influenza is defined as 1 day before fever onset until 24 hours after fever ends.

Prevention and control:

Various measures of pharmacological and non-pharmacological intervention are applied by developing countries to limit and prevent the disease.

Non-pharmacological measures include: personal hygiene, washing hands by soap, covering the mouth and nose while coughing and sneezing, avoiding crowded places, cancellation of social events such as weddings, and closure of schools and malls. Mandatory isolation of cases and quarantine of close contacts. For the health workers, they should take the clinical samples with adequate biosafety facilities, protective equipment should be used during the procedures. For the pharmacological measures: antiviral drugs (oseltamivir and zanamivir) are recommended and the drug of choice for H1N1 influenza, it should be given within 48 hours of symptom onset, and the priority for these patients with risk factors for severe disease such as old patient (>65 years), pregnant women, patient with immunosuppression or chronic disease like asthma, and young children (148 hours after symptoms onset. Antiviral prophylaxis should be given to health workers for a duration of up to 6 weeks for oseltamivir and 4 weeks for zanamivir, also the close contact and patient who are not provided with prophylaxis should take early treatment with an antiviral drug.


The vaccine is available in a few countries. It is the most effective measure to prevent influenza-associated morbidity and mortality. The vaccine is based on A/California/07/2009 (H1N1) strain, it is available in both live-attenuated and inactivated formulations. A single dose is adequate for those older than 9 years, and immune response was seen in 80% to 96%of adults aged 18 to 64 years and 56% to 80% of adults aged 65 years or older. Children younger than 10 years will require two doses separated by at least 21 days. The live attenuated vaccine is only for persons aged 2 to 49 years who are not pregnant, immunocompetent, and have no chronic diseases, and it is contraindicated in children younger than five years who have asthma, children receiving long term aspirin, and those in close contact with immunosuppressed persons. The inactivated vaccine is contraindicated in patients with severe allergic conditions to eggs or any component of the vaccine.


H1N1 is a subtype of influenza a virus that triggers upper and lower respiratory tract infections, the number of laboratories- in Saudi Arabia as of 30 December 2009 was 15850, with 124 deaths… It is spread through droplets of coughing or sneezing, by direct or indirect contact with the respiratory secretions of the infected person, by proximity to virus-contaminated items (fomites), and through touch with the nose or mouth, and by inhalation of infectious aerosols. Patients usually have a fever, cough, sore throat, malaise, headache, myalgia, arthralgia, and muscle fatigue, it can also cause any inflammation of the gastrointestinal tract. Public grooming, hand washing soap, and mouth, and nose covering when coughing and sneezing are prevention strategies and antiviral prophylaxis can also be used. There are two types of live attenuated and inactivated vaccines that is used respectively.


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