* What is swine influenza?
* What are the implications for human health?
* Where have human cases occurred?
* How do people become infected?
* Is it safe to eat pork and pork products?
* Which countries have been affected by outbreaks in pigs?
* What about the pandemic risk?
* Is there a human vaccine to protect from swine influenza?
* What drugs are available for treatment?
* What should I do if I am in regular contact with pigs?
* How can I protect myself from getting swine influenza from infected people?
* What should I do if I think I have swine influenza?
What is swine influenza?
Swine influenza, or “swine flu”, is a highly contagious acute respiratory disease of pigs, caused by one of several swine influenza A viruses. Morbidity tends to be high and mortality low (1-4%). The virus is spread among pigs by aerosols, direct and indirect contact, and asymptomatic carrier pigs. Outbreaks in pigs occur year round, with an increased incidence in the autumn and winter in temperate zones. Many countries routinely vaccinate swine populations against swine influenza.
Swine influenza viruses are most commonly of the H1N1 subtype, but other subtypes are also circulating in pigs (e.g., H1N2, H3N1, H3N2). Pigs can also be infected with avian influenza viruses and human seasonal influenza viruses as well as swine influenza viruses. The H3N2 swine virus was thought to have been originally introduced into pigs by humans. Sometimes pigs can be infected with more than one virus type at a time, which can allow the genes from these viruses to mix. This can result in an influenza virus containing genes from a number of sources, called a "reassortant" virus. Although swine influenza viruses are normally species specific and only infect pigs, they do sometimes cross the species barrier to cause disease in humans.
What are the implications for human health?
Outbreaks and sporadic human infection with swine influenza have been occasionally reported. Generally clinical symptoms are similar to seasonal influenza but reported clinical presentation ranges broadly from asymptomatic infection to severe pneumonia resulting in death.
Since typical clinical presentation of swine influenza infection in humans resembles seasonal influenza and other acute upper respiratory tract infections, most of the cases have been detected by chance through seasonal influenza surveillance. Mild or asymptomatic cases may have escaped from recognition; therefore the true extent of this disease among humans is unknown.
Where have human cases occurred?
Since the implementation of IHR(2005)1 in 2007, WHO has been notified of swine influenza cases from the United States and Spain.
How do people become infected?
Humans usually contract swine influenza from infected pigs, however, some cases lack contact history with pigs or environments where pigs have been located. Human-to-human transmission has occurred in some instances but was limited to close contacts and closed groups of people.
Is it safe to eat pork and pork products?
Yes. Swine influenza has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs. The swine influenza virus is killed by cooking temperatures of 160°F/70°C, corresponding to the general guidance for the preparation of pork and other meat.
Which countries have been affected by outbreaks in pigs?
Swine influenza is not notifiable to international animal health authorities (OIE, www.oie.int), therefore its international distribution in animals is not well known. The disease is considered endemic in the United States. Outbreaks in pigs are also known to have occurred in North America, South America, Europe (including the UK, Sweden, and Italy), Africa (Kenya), and in parts of eastern Asia including China and Japan.
What about the pandemic risk?
It is likely that most people, especially those who do not have regular contact with pigs, do not have immunity to swine influenza viruses that can prevent the virus infection. If a swine virus establishes efficient human-to human transmission, it can cause an influenza pandemic. The impact of a pandemic caused by such a virus is difficult to predict: it depends on virulence of the virus, existing immunity among people, cross protection by antibodies acquired from seasonal influenza infection and host factors.
Is there a human vaccine to protect against swine influenza?
There are no vaccines that contain the current swine influenza virus causing illness in humans. It is not known whether current human seasonal influenza vaccines can provide any protection. Influenza viruses change very quickly. It is important to develop a vaccine against the currently circulating virus strain for it to provide maximum protection to the vaccinated people. This is why WHO needs access to as many viruses as possible in order to select the most appropriate candidate vaccine virus.
What medicines are available for treatment?
There are two classes of such medicines, 1) adamantanes (amantadine and remantadine), and 2) inhibitors of influenza neuraminidase (oseltamivir and zanamivir).
Most of the previously reported swine influenza cases recovered fully from the disease without requiring medical attention and without antiviral medicines.
Some influenza viruses develop resistance to the antiviral medicines, limiting the effectiveness of treatment. The viruses obtained from the recent human cases with swine influenza in the United States are sensitive to oselatmivir and zanamivir but resistant to amantadine and remantadine.
Information is insufficient to make recommendations on the use of the antivirals in treatment of swine influenza virus infection. Clinicians should make decisions based on the clinical and epidemiological assessment and harms and benefits of the treatment of the patient2. For the ongoing outbreak of the swine influenza infection in the United States and Mexico, national and local authorities are recommending use oseltamivir or zanamivir for treatment of the disease based on the virus’s susceptibility profile.
What should I do if I am in regular contact with pigs?
Even though there is no clear indication that the current human cases with swine influenza infection are related to recent or ongoing influenza-like disease events in pigs, it would be advisable to minimize contact with sick pigs and report such animals to relevant animal health authorities.
Most people are infected through prolonged, close contact with infected pigs. Good hygiene practices are essential in all contact with animals and are especially important during slaughter and post-slaughter handling to prevent exposure to disease agents. Sick animals or animals that died from disease should not be undergoing slaughtering procedures. Follow further advice from relevant national authorities.
Swine influenza has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs. The swine influenza virus is killed by cooking temperatures of 160°F/70°C corresponding to the general guidance for the preparation of pork and other meat.
How can I protect myself from getting swine influenza from infected people?
In the past, human infection with swine influenza was generally mild but is known to have caused severe illness such as pneumonia For the current outbreaks in the United States and Mexico however, the clinical pictures have been different. None of the confirmed cases in the United States have had the severe form of the disease and the patients recovered from illness without requiring medical care. In Mexico, some patients reportedly had the severe form of the disease.
To protect yourself, practice general preventive measures for influenza:
* Avoid close contact with people who appear unwell and who have fever and cough.
* Wash your hands with soap and water frequently and thoroughly.
* Practice good health habits including adequate sleep, eating nutritious food, and keeping physically active.
If there is an ill person at home:
* Try to provide the ill person a separate section in the house. If this is not possible, keep the patient at least 1 meter in distance from others.
* Cover mouth and nose when caring for the ill person. Masks can be bought commercially or made using the readily available materials as long as they are disposed of or cleaned properly.
* Wash your hands with soap and water thoroughly after each contact with the ill person.
* Try to improve the air flow in the area where the ill person stays. Use doors and windows to take advantage of breezes.
* Keep the environment clean with readily available household cleaning agents.
If you are living in a country where swine influenza has caused disease in humans, follow additional advice from national and local health authorities.
What should I do if I think I have swine influenza?
If you feel unwell, have high fever, cough and/or sore throat:
* Stay at home and keep away from work, school or crowds as much as possible.
* Rest and take plenty of fluids.
* Cover your mouth and nose with disposable tissues when coughing and sneezing and dispose of the used tissues properly.
* Wash your hands with soap and water frequently and thoroughly, especially after coughing or sneezing.
* Inform family and friends about your illness and seek help for household chores that require contact with other people such as shopping.
If you need medical attention:
* Contact your doctor or healthcare provider before travelling to see them and report your symptoms. Explain why you think you have swine influenza (for example, if you have recently travelled to a country where there is a swine influenza outbreak in humans). Follow the advice given to you for care.
* If it is not possible to contact your healthcare provider in advance, communicate your suspicion of having swine influenza immediately upon arrival at the healthcare facility.
* Take care to cover your nose and mouth during travel.
* What is swine influenza?
The audiences for this guidance document are the National Focal Points for the International Health Regulations (IHR(2005)) and competent national public health authorities. The primary focus of this guidance document is global surveillance. It also gives some suggestions on the types of signals that Member States and IHR States Parties can capture in their event-based
surveillance. These signals can aid identification of individuals for whom investigation of swine influenza A(H1N1) virus infection is warranted.
This is an interim WHO guidance on the global surveillance of the emerging swine influenza A(H1N1) virus infection. This is a living document that will be reviewed on a weekly basis and modified in accordance with changes in the epidemiology of this virus. As the event evolves, there will be a need to switch surveillance activities to the longer-term monitoring of the
disease. WHO will alert countries when a change in surveillance objectives and methods occurs. WHO’s data requirements will remain as flexible as possible to accommodate different surveillance systems and reporting capacity around the world. This document will form part of a suite of guidance documents being produced by WHO in response to this public health emergency of international concern as determined by the Director General of WHO on 25 April 2009. New influenza virus sub-types and clusters of unknown and unusual disease are notifiable to WHO in accordance with the Annex 2 decision instrument of the IHR (2005). At this early stage of the outbreak of swine influenza A(H1N1) virus, the main aims of surveillance are the early warning of virus spread and laboratory confirmation of virus
circulating in new geographical areas and countries. Accordingly, WHO encourages all Member States and IHR States Parties to enhance their surveillance and diagnostic capacity for influenza and other acute respiratory infections, building on exiting surveillance structure and resources. Objectives of enhanced global surveillance for human infections with swine influenza A(H1N1) virus Specific objectives of this surveillance activity are to guide global prevention and control activities through the following actions:
1. Detect and confirm cases of swine influenza A(H1N1) virus infection
2. Establish the extent of international spread of swine influenza A(H1N1) virus infection
3. Assist in the early severity assessment of the disease
Case definitions for infections with swine influenza A(H1N1) Virus
In order to understand the spectrum of severity of the disease caused by swine influenza
A(H1N1) virus infection , the clinical case description includes both mild form of influenza-like illness (ILI) and more severe forms (lower respiratory tract infections including pneumonia and severe acute respiratory illness (SARI)). In addition, asymptomatic laboratory-confirmed
infections should be reported. The following case definitions are for the purpose of reporting probable and confirmed cases of swine influenza A(H1N1) virus infection to WHO.
Clinical case description Acute febrile respiratory illness (fever >38°C ) with the spectrum of disease from influenza-like illness to pneumonia.
1. A Confirmed case of swine influenza A(H1N1) virus infection is defined as an individual with laboratory confirmed swine influenza A(H1N1) virus infection by one or more of the following tests*:
• real-time RT-PCR
• viral culture
• four-fold rise in swine influenza A(H1N1) virus specific neutralizing antibodies.
2. A Probable case of swine influenza A(H1N1) virus infection is defined as an individual with an influenza test that is positive for influenza A, but is unsubtypable by reagents used to detect seasonal influenza virus infection OR A individual with a clinically compatible illness or who died of an unexplained acute respiratory illness who is considered to be epidemiologically linked to a probable or
* Note: The test(s) should be performed according to the most currently available guidance on testing (http://www.who.int/csr/disease/swineflu/en/index.html).
Reporting requirements for confirmed and probable cases of swine influenza A(H1N1)
Under the IHR (2005), immediate reporting to WHO is required for human influenza due to a new influenza virus sub-type. All information will be treated in accordance with the IHR (2005) provisions. If available, countries should report travel history of case(s). Reports should be sent by the National IHR Focal Point to the relevant WHO IHR Contact Point at the WHO Regional Office, the WHO Country Representative, where applicable, and WHO headquarters in Geneva should be copied on the correspondence
Reporting of individual(s) or clusters under investigation for swine influenza A(H1N1) virus infection
Countries that identify unusual clusters of acute respiratory illness should immediately notify
WHO. These consultations will not be reflected in global statistics until their investigation confirms that they are laboratory-confirmed or probable cases. Definition of cluster
A cluster is defined as two or more persons presenting with manifestations of unexplained, acute respiratory illness with fever >38°C or who died of an unexplained respiratory illness and that are detected with onset of illness within a period of 14 days and in the same geographical area and/or are epidemiologically linked.
Triggers/signals for the investigation of possible cases of swine influenza A(H1N1). The primary focus of early investigation is to trigger the initial investigation. Specific triggers include:
• Clusters of cases of unexplained ILI or acute lower respiratory disease
• Severe, unexplained respiratory illness occurring in one or more health care worker(s) who provide care for patients with respiratory disease
• Changes in the epidemiology of mortality associated with the occurrence of ILI or lower respiratory tract illness, an increase in deaths observed from respiratory illness or an increase in the occurrence of severe respiratory disease in previously healthy adults or adolescents
• Persistent changes noted in the treatment response or outcome of severe lower respiratory illness. Epidemiological risk factors that should raise suspicion of swine influenza A(H1N1) include:
• Close contact# to a confirmed case of swine influenza A(H1N1) virus infection while the
case was ill
• Recent travel to an area where there are confirmed cases of swine influenza A (H1N1) #Close contact: having cared for, lived with, or had direct contact with respiratory secretions or body fluids of a probable or confirmed case of swine influenza A(H1N1). Member States reporting cases of swine influenza A(H1N1) virus infection for the first time As soon as a the National IHR Focal Point or competent national public health authority notifies WHO of the first laboratory-confirmed or probable case(s) of swine influenza A(H1N1), WHO will make available the case summary form and database for the recording of detailed clinical, laboratory and epidemiological data in accordance with WHO pandemic surveillance guidelines. WHO Swine Influenza A(H1N1) Case Summary Form for case-based data collection [pdf 318kb]
A(H1N1) daily aggregated indicators [pdf 64kb]
WHO also requires information to assess whether sustained community transmission isoccurring. Wherever possible, a detailed exposure history should be collected by Member States and shared with WHO. Member States where cases of swine influenza A(H1N1) virus infection have already been reported Until further notice, the National IHR Focal Points or competent national public health authorities should report to WHO all probable and confirmed cases on a daily basis. Deaths should be reported for both probable and confirmed cases. A reporting format has been posted on the web (link).
WHO will present the cumulative number of cases for global reporting back to Member States and the public. This activity will only continue for the initial period of data collection. In order to understand the severity of the disease it is very important that comprehensive data collection and follow up is carried out for all probable and confirmed cases of swine influenza A(H1N1) virus infection. WHO’s data requirements are detailed in the Global Surveillance during an Influenza Pandemic Version 1 Updated draft April 2009 (Comprehensive Assessment, Clinical characteristics: Database of information for 100 cases). A WHO Swine Influenza A(H1N1) Case Summary Form has been posted on the web (Link). Member States are encouraged to report on methods used for the selection of cases for inclusion into the dataset in order to assist the interpretation of any result. Confirmed and probable cases reported are to be attributed to the country or territory in which they are currently located or where they have died.
The reported case-based data will be used by WHO to assess the clinical disease spectrum and severity, and guide treatment recommendations.
National Influenza Centres and National reference centres should continue to report virologist information to Flu Net.
Access to Laboratory Confirmation Countries without current capacity to confirm swine influenza A(H1N1) should contact WHO to arrange access to a laboratory with this capability.