Flu is a contagious respiratory tract infection caused by Influenza viruses. Influenza viruses are of three types A, B and C. Type A has caused most human outbreaks whereas type B and C are less often associated with severe human infections.

Swine flu is a respiratory infection seen in pigs due to Influenza viruses. They spread among pigs due to mutual contact but usually do not spread to the Human beings. It may spread to humans due to close contact with the pigs or environments contaminated with swine influenza viruses. Subsequently human to human spread may occur via coughing and sneezing.

Influenza viruses have two surface antigens (proteins) – the H (hemagglutinin) and the N (neuraminidase). These help the virus to adhere to the respiratory tract lining. These H and N antigens also have some difference structurally between virus groups to virus group. These differences are conveyed by a specific number assigned to each antigen. Various combinations of differently numbered antigens give strain specificity to the viruses. eg. The SARS outbreak was caused by the strain of influenza virus A H5N1. The A H1N1 has been usually infecting the pigs only and this is the first major outbreak of this new virus. Hence humans do not have immunity against this virus strain.

Cases of influenza-like illness were first reported in Mexico on March 18; the outbreak was subsequently confirmed as swine influenza A. As of 1600 GMT, 3 May 2009, 18 countries have officially reported 898 cases of influenza A (H1N1) infection. Mexico has reported 506 confirmed human cases of infection, including 19 deaths. The United States Government has reported 226 laboratory confirmed human cases from 30 states, including one death. The following countries have reported laboratory confirmed cases with no deaths - Austria (1), Canada (85), China, Hong Kong Special Administrative Region (1), Costa Rica (1), Denmark (1), France (2), Germany (8), Ireland (1), Israel (3), Italy (1), Netherlands (1), New Zealand (4), Republic of Korea (1), Spain (40), Switzerland (1) and the United Kingdom (15). So far no cases have been reported from India.

An influenza pandemic occurs when a new influenza virus appears against which the human population has no immunity, resulting in epidemics worldwide with enormous numbers of deaths and illness. With the increase in global transport, as well as urbanization and overcrowded conditions, epidemics due the new influenza virus are likely to quickly take hold around the world. Currently the WHO has declared a phase 5 pandemic level for influenza H1N1. (Phase 5 - Still not a pandemic, but spread of disease between humans is occurring in more than one country of one WHO region).

It is usually seen in young previously not symptomatic individuals. The usual symptoms of fever, cough, sore throat, body aches, headache, chills and fatigue, diarrhea and vomiting are all possible. Persons with these symptoms should call their health care provider promptly. In young children or infants there may be lethargy, poor feeding, reduced activity, cyanosis, apathy, altered mental status and extreme irritability.

Though flu would be mild in most patients, it can cause severe pneumonia, distress and breathing problems in some individuals that may even lead to death.

The duration of illness is typically 4-6 days. The infectious period for a confirmed case is defined as 1 day prior to the onset of symptoms to 7 days after onset. Once a human becomes infected, he or she can then spread the virus to other humans, presumably in the same way as seasonal influenza is spread (ie, via coughing or sneezing).

A confirmed case of Swine origin influenza virus (S-OIV) infection is defined as a person with an acute febrile respiratory illness with laboratory confirmed S-OIV infection at WHO by one or more of the following tests: Real-time RT-PCR and/or viral culture.

Swine influenza should be suspected in a person with acute febrile respiratory illness with onset

•	Within 7 days of close contact with a person who is a confirmed case of S-OIV infection, or
•	Within 7 days of travel to community where there are one or more confirmed cases of S-OIV infection, or
•	Resides in a community where there are one or more confirmed cases of S-OIV infection.

Treatment is largely supportive and consist of bedrest, increased fluid consumption, cough suppressants, and antipyretics and analgesics (eg, acetaminophen, nonsteroidal anti-inflammatory drugs) for fever and myalgias. Oseltamavir and Zanamivir have been approved for the use in influenza A H1N1. For dosage and method of taking these drugs one must contact your doctor.

•	Home isolation of affected individuals for seven days.
•	Encouraging the use of face masks while in community.
•	Frequent hand washing with soap and water.
•	School dismissal and childcare facility closure.
•	Social distancing-reducing group meeting etc.
•	Use of antiviral chemoprophylaxis (for details meet your doctor).

No the existing vaccines do not have this strain and hence cannot confer immunity to patients against this new strain - A H1N1.

Last Updated: 3rd May 2009