pandemic influenza


Influenza (“flu”) is a respiratory illness that can be transmitted from person to person. Flu viruses are of two main genetic types: Influenza A and B. Influenza A strains are further identified by two important surface proteins that are responsible for virulence: hemagglutinin (H) and neuraminidase (N).

Swine flu occurs naturally and may cause outbreaks among wild and domestic swine. People do not normally get swine flu, but each year CDC identifies a few isolated cases of human flu that are caused by flu strains typically associated with swine.

What is swine influenza?
Swine influenza is a respiratory disease of pigs caused by type A influenza viruses. In affected pigs, it causes cough, fever, nasal discharge, lethargy and difficulty breathing. Influenza A viruses are classified by two components of the viral surface, hemagglutinin (H) and neuraminidase (N). Different types of influenza A viruses are infectious to avian and mammalian species. Pigs and people are susceptible to influenza A viruses from both avian and mammalian sources. Infection with multiple viruses can lead to the creation of new “reassorted” viruses with components of pig, bird and human flu origin. Classical swine flu (H1N1) was first isolated in 1930, and many other subtypes have since been identified (e.g. H3N2, H1N2). In the United States, swine influenza outbreaks are most common in fall and winter. In Minnesota, we see peaks of swine flu activity in April through May and September through November.

Avian flu (“bird flu”) is caused by viruses that occur naturally among wild birds, and that may also affect domestic poultry. In 1997 a new H5N1 strain of avian flu emerged in Asia, and has since caused millions of deaths among domestic poultry, and hundreds of deaths in humans. Health officials have been concerned that this strain could cause a human pandemic, and governments around the world have carried out a number of preparedness activities, including vaccine development and stockpiling, and planning for continuity of services.

Pandemic flu is caused when a novel strain of human flu (i.e., one that spreads from person to person) emerges and causes a global outbreak, or pandemic, of serious illness. Because there is little natural immunity, the disease is often more severe than is typical of seasonal flu.

Influenza is an infectious disease caused by the influenza virus. The disease is commonly called flu or grippe. The word influenza is sometimes used to refer generally to either influenza or similar illnesses. The symptoms of influenza include chills, fever, headache, aches, and weakness. The symptoms usually disappear in about a week. The patient's resistance may be lowered, so that secondary infections, such as bacterial pneumonia, follow the influenza.

How influenza spreads. Influenza is mainly a respiratory disease. The virus is inhaled and comes in contact with cells of the upper air passages. It penetrates the cells that line these passages and reproduces within them. In time, new influenza viruses are released from the infected cells and infect other cells along the respiratory tract. Influenza may spread deep within the lungs. The virus may also be carried away in exhaled air and infect other people.

One of the worst global epidemics of influenza occurred in 1918-1919. About 20 million people, including more than 500,000 Americans, died in this epidemic. In 1957-1958, Asian flu caused a worldwide epidemic, as did Hong Kong flu in 1968-1969. Far fewer deaths resulted from these epidemics, due largely to the control of secondary infections with antibiotics.




What is pandemic influenza A(H1N1) 2009 virus?

The symptoms of pandemic influenza are non-specific and may be similar to seasonal influenza infections. The case definitions below will enable you to recognise a case that may be infected with pandemic influenza, and classify them into one of two categories:

ILI (Influenza Like Illness) – Mild Disease:
An individual with recent onset of an influenza-like illness (ILI), which may include fever ≥380C PLUS ONE OR MORE of the following acute respiratory symptoms (sore throat, rhinorrhoea / nasal congestion, cough or other signs part of the respiratory complex, myalgia, diarrhoea ).

SARI (Severe Acute Respiratory Infection) –
Moderate to Severe Disease:

Persons 2 days to < 3 months old:
Any child with diagnosis of suspected sepsis or physician diagnosed lower respiratory tract infection (LRTI) irrespective of signs and symptoms. Patient presenting within 7 days of the onset of illness.

≥ 3 months old to < 5 years old:
Any child ≥ 3 months to < 5 years with physician-diagnosed acute lower respiratory infection (LRTI) including bronchiolitis, pneumonia, bronchitis and pleural effusion. Patient presenting within 7 days of the onset of illness

≥ 5 years old:
Any person presenting with: sudden onset of fever (>38ºC) AND cough or sore throat AND shortness of breath, or difficulty breathing with or without clinical or radiographic findings of pneumonia. Patient presenting within 7 days of the onset of illness.

Features of severe illness
The criteria for severe pneumonia according to the WHO integrated management of childhood illness (IMCI) guidelines are below:

Any child age 2 months up to 5 years with:
Cough or difficult breathing, AND with
Any general danger signs (unable to drink or breast-feed, vomits everything, convulsions, lethargy or unconsciousness), OR
Chest indrawing or stridor in a calm child.

Severity criteria in adults of any age group include: respiratory distress, dyspnoea, hypotension and / or evidence of hypoxia.
Although data on the spectrum of illness is limited with pandemic influenza A(H1N1) 2009 clinicians should expect complications to be similar to those seen with seasonal influenza and will include: exacerbation of underlying chronic medical conditions, upper respiratory tract disease (sinusitis, otitis media, croup), lower respiratory tract disease (pneumonia, bronchiolitis), cardiac (myocarditis, pericarditis), musculoskeletal (myositis, rhabdomyolysis), neurologic (acute and post infectious encephalopathy- encephalitis and febrile seizures), and secondary bacterial pneumonia.

Source :
The National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS) In collaboration with: The South African National Department of Health and World Health Organisation (WHO).

What is swine influenza?
Influenza Defined
Influenza Viruses - Types, Subtypes, and Strains
What is pandemic influenza A(H1N1) 2009 virus?
Definitions for identification of pandemic influenza A(H1N1) 2009
Case Management & Infection Control
Who should be tested?
Step-by-step guide for specimen collection, storage and transportation
Doctors/Nurses directions to Patients/Parents
How Influenza Viruses Change: Drift and Shift
The 2009 Influenza Pandemic
International Health Regulations
Vaccine Development and Use
Naming the Virus Strain
Information for Families and Visitors
New Pandemic Influenza A (H1N1) 2009
Pandemic (H1N1) 2009 Influenza Guidance
Recent Results from Studies with the new 2009 A/H1N1 Influenza A Virus
Continued pandemic influenza virus detections across Europe with increased activity in the UK (Northern Ireland)
Highly Pathogenic Avian Influenza Virus H5N1 and Wild Birds