Pandemic influenza refers to a global disease outbreak. A flu pandemic occurs when a new influenza type A virus emerges for which people have little or no immunity, and for which there is no vaccine. The disease spreads easily person-to-person, causes serious illness, and can sweep across the country and around the world in a very short time. Such a virus is likely to have origins from avian viruses or possibly from other animal sources (e.g., pigs). In the case of the current pandemic influenza found normally in pigs is causing illness in humans. This virus is known as Novel H1N1 (swine flu). Currently, the World Health Organization has elevated the Pandemic Level to Level 6. This is the highest level for any Pandemic.
CLINICAL BACKGROUND INFORMATION
Historically, influenza has caused outbreaks of respiratory illness for centuries, including three pandemics in the 20th century. There are three types of influenza viruses: type A, B and C. Only type A influenza viruses cause pandemics. Seasonal influenza outbreaks can be caused by either type A or type B influenza viruses. Influenza type C viruses cause mild illness in humans but do not cause epidemics or pandemics. This newsletter is aimed at protecting healthcare workers during the current pandemic; therefore, the focus will be on the characteristics of type A influenza viruses.
Of the three types of influenza viruses, only type A is divided into subtypes. Three different subtypes (i.e., H1N1, H2N2, and H3N2) have caused pandemics in the 20th century.
Seasonal, avian, and H1N1 (swine flu) can occur in humans.
It is important to understand the basics of these three types of influenza.
Seasonal influenza refers to the periodic outbreaks of acute onset viral respiratory infection caused by circulating strains of human influenza A and B viruses. Seasonal influenza generally occurs most frequently during the winter months. Between 5-20 percent of the population may be infected annually. Each year, a trivalent influenza vaccine is prepared in advance of the anticipated seasonal outbreak and it includes those strains (two types A and one type B) that are expected to be most likely to circulate in the upcoming “flu” season. Influenza vaccine is currently targeted toward those at greatest risk of influenza-related complications and their contacts, such as healthcare workers.
Avian influenza (H5N1), also known as the bird flu, is caused by type A influenza viruses that infect wild birds and domestic poultry. The highly pathogenic H5N1 is one of the few avian influenza viruses to have crossed the species barrier to infect humans, and it is the most deadly of those that have crossed the barrier. Most cases of highly pathogenic H5N1 infection in humans have resulted from contact with infected poultry or surfaces contaminated with secretion/excretions from infected birds. Because all influenza viruses have the ability to change, scientists are concerned that highly pathogenic H5N1 avian influenza virus one day could be able to sustain human-to-human transmission.
Novel Strain H1N1, also known as swine flu, is caused by type A influenza viruses that infect pigs. Novel H1N1 (referred to as “swine flu” early on) is a new influenza virus causing illness in people. This new virus was first detected in people in the United States in April 2009. Other countries, including Mexico and Canada, have reported people sick with this new virus. This virus is spreading from person-to-person, probably in much the same way that regular seasonal influenza viruses spread.
Signs and Symptoms of H1N1 (swine flu)
The symptoms of novel H1N1 flu virus in people are similar to the symptoms of seasonal flu and include:
· sore throat
· runny or stuffy nose
· body aches
A significant number of people who have been infected with this virus also have reported diarrhea and vomiting. Also, like seasonal flu, severe illnesses and death has occurred as a result of illness associated with this virus.
A person who is at high-risk for complications of novel influenza (H1N1) virus infection is defined as the same for seasonal influenza at this time.
- Children younger than 5 years old.
- Adults 65 years of age and older
- Persons with the following conditions:
- Chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, hematological (including sickle cell disease), neurologic, neuromuscular, or metabolic disorders (including diabetes mellitus)
- Immunosuppression, including that caused by medications or by HIV
- Pregnant women
- Persons younger than 19 years of age who are receiving long-term aspirin therapy
- Residents of nursing homes and other chronic-care facilities.
Transmission of Influenza
Transmission of novel influenza A (H1N1) is being studied as part of the ongoing outbreak investigation, but limited data available indicate that this virus is likely transmitted in ways similar to other influenza viruses. Seasonal human influenza viruses are thought to be transmitted between persons primarily through large-particle respiratory droplet transmission (e.g., when an infected person coughs or sneezes near a susceptible person). Transmission via these large-particle droplets requires close contact between source and recipient persons because droplets do not remain suspended in the air and generally travel only a short distance (<6 feet). Contact with contaminated surfaces is another possible source of transmission and transmission via small-droplet nuclei (also called “airborne” transmission) might also occur, but the contribution of these modes of transmission to influenza epidemiology is uncertain. Because data on the transmission of novel H1N1 viruses are limited, the potential for ocular, conjunctival, or gastrointestinal infection is unknown. Since this is a novel influenza A (h1N1) virus in humans, transmission from infected persons to close contacts might be common. All respiratory secretions and bodily fluids (diarrheal stool) of novel influenza A (H2N2) cases should be considered potentially infectious.
Close contact, is defined as having cared for or lived with a person who is a confirmed, probable or suspected case of novel influenza A (H1N1), or having been in a setting where there was a high likelihood of contact with respiratory droplets and/or body fluids of such a person. Examples of close contact include kissing or embracing, sharing eating or drinking utensils, physical examination, or any other contact between persons likely to result in exposure to respiratory droplets. Close contact typically does not include activities such as walking by an infected person or sitting across from a symptomatic patient in a waiting room or office.