The 2009 flu pandemic is a global outbreak of a new strain of a influenza A virus subtype H1N1, officially named the "new H1N1", first identified in April 2009, and commonly called "Swine flu." It is thought to be a reassortment of four known strains of influenza A virus, one endemic in (normally infecting) humans, one endemic in birds, and two endemic in pigs (swine). Transmission of the new strain is human-to-human, with cooked pork products safe to eat as the virus cannot be transmitted by eating foods.
The outbreak began in Mexico, with evidence that Mexico was already in the midst of an epidemic for months before the outbreak was recognized. Soon after, its government closed down most of Mexico City's public and private offices and facilities to help contain the spread. In early June, as the virus spread globally, the World Health Organization (WHO) declared the outbreak to be a pandemic, but also noted that most illnesses were of "moderate severity."
The virus typically spreads from coughs and sneezes or by touching contaminated surfaces and then touching the nose or mouth. Symptoms, which can last up to a week, are similar to those of seasonal flu, and may include fever, sneezes, sore throat, coughs, headache, and muscle or joint pains. In an attempt to slow the spread of the illness, a number of countries, especially in Asia, have quarantined airline passengers with flu symptoms, while some are also pre-screening passengers. WHO does not expect to have a full vaccine before the end of 2009, and vaccines available sooner may be limited and given first to healthcare workers, pregnant women, and other higher risk groups. Two or three injections will be required for maximum immunity from both the swine flu and seasonal flu. There is also concern if the new virus mutates further, it could become more virulent and less susceptible to any new vaccine.

Symptoms and expected severity

The signs of infection with swine flu are similar to other forms of influenza, and include a fever, coughing, headaches, pain in the muscles or joints, sore throat, chills, fatigue and runny nose.
Diarrhea, vomiting and neurological problems have also been reported in some case. People at higher risk of serious complications included people age 65 years and older, children younger than 5 years old, pregnant women, and people of any age with underlying medical conditions, such as asthma, diabetes, obesity, heart disease, or a weakened immune system (e.g., taking immunosuppressive medications or infected with HIV).
Symptoms that may require medical attention
Certain symptoms may require emergency medical attention. In children signs of respiratory distress, for instance, those might include blue lips and skin, dehydration, rapid breathing, excessive sleeping, seizures and significant irritability that includes a lack of desire to be held. In adults, shortness of breath, pain in the chest or abdomen, sudden dizziness or confusion may indicate the need for emergency care. In both children and adults, persistent vomiting or the return of flu-like symptoms that include a fever and cough may require medical attention.

Influenza infection can cause pneumonia leading to death. This is typically described as either viral pneumonia, which has a rapid onset, often within one day after infection, or bacterial pneumonia, which often begins a week after infection after symptoms have begun to subside.
Viral pneumonia has sometimes been attributed to "cytokine storm", in which an overly active immune response damages the lungs.
Bacterial pneumonia is a secondary infection resulting from a weakened ability to clear common bacteria from the lower lungs, combined with reduced alveolar macrophage activity which makes it more difficult for the body to fight infection. Bacteria that cause pneumonia include Pneumococcus, Staphylococcus, and Hemophilus influenzae.

Personal hygiene
1. Vaccination when available
2. Thorough and frequent hand-washing
3. A balanced diet with fresh fruits and vegetables, whole grains, and lean protein.
4. Sufficient sleep, regular exercise, and avoiding crowds.

Airborne virus prevention
Masks may be of benefit in "crowded settings" or for people who are in "close contact" with infected persons, defined as 1 meter or less by the World Health Organization (WHO) and 6 feet or less by the U.S. Occupational Safety and Health Administration. In these cases the CDC recommended respirators classified as N95, but it is unknown whether they would prevent swine flu infection. According to mask manufacturer 3M , there are no "established exposure limits for biological agents" such as swine flu virus.