1. What is Influenza
2. What is the Avian Flu
3. Guidelines on Avian Flu Prevention
4. Case Definitions for Human Influenza A (H5N1) Infection
5. FAQs for Public about Pandemic Flu [Source: Centre for Health Protection, Department of Health, HKSAR]
6. Influenza Outbreak and Influenza Pandemic Action Plan (October 2005)
7. Herbal Decoctions for the Prevention and Treatment of Influenza (provided by the School of Chinese Medicine, CUHK, for reference)
8. Video clip "Avian Flu" (Chinese version only, for viewing via CUHK Intranet)
9. Talks

1. What Is Influenza?

Influenza is caused by a virus that attacks mainly the upper respiratory tract: the nose, throat and bronchi and rarely, the lungs.

The Virus:  

Influenza viruses are defined by 2 different surface antigens: Haemagglutinin (H) and Neuraminidase (N).

The viruses can be classified into 3 groups: A, B, and C, whereas Influenza A can cause pandemics and can be further divided into 16 H subtypes and 9 N subtypes. Only A and B are of concern to human health. Influenza A causes larger epidemics like worldwide pandemics, whereas Influenza B is often limited to localized outbreaks.

The infection usually lasts for about a week, characterized by a sudden onset of high fever, muscle pain, headache or severe malaise, non-productive cough, sore throat, and runny nose. Most people recover within 1 to 2 weeks.

High-risk groups

To the very young, the elderly and people suffering from medical conditions such as lung diseases, diabetes, cancer, kidney or heart problems, influenza poses a serious risk. Immunosuppressive and residents in long-term care facilities are more prone to be infected too.

Mode of Transmission, Peak season and Incubation period

The virus is transmitted by air droplets and spreads easily when infected individuals cough or sneeze. Influenza spreads very quickly among the community, especially in crowded circumstances. Cold and dry weather enables the virus to survive longer outside the body; the peak season in Hong Kong is from February to March and from October to November.

The incubation period is 1 to 4 days, which means the infected person can be infectious before symptoms are developed, i.e. from the first exposure day to the 7th day after symptoms have developed.

Diagnosis

Mild respiratory illnesses caused by influenza are hard to be distinguished from illnesses caused by other respiratory pathogens (e.g. common cold) based on symptoms alone. Therefore, unless an outbreak occurred in the community, laboratory confirmation is required between the annual influenza epidemics.

Prevention

• Build good body resistance through maintaining a healthy life-style.
• Maintain good personal hygiene. Consult a doctor and wear a mask to prevent the spread of diseases. Remember, frequent hand washing is the most crucial practice.

Influenza vaccination. Internationally-licensed vaccines have proved to be efficacious and safe. Although antiviral drugs are available, the emergence of resistant viral mutants to the lungs, the occasional side effects, drug costs and limited availability during major outbreaks highlight the role of vaccination as the primary preventive measure against influenza.  

Influenza Vaccination:

The main purpose is to avoid severe influenza and its compliances. In addition to high-risk groups, vaccination is generally recommended to health care workers and household contacts of high-risk persons.

Influenza vaccination is also recommended as a measure for better surveillance of SARS outbreaks and for the prevention of emergence of Human Avian Influenza.

Vaccine Type

It is an inactive, non-infectious viral. Boosters are unhelpful as wild virus changes each year.

Number of doses

Influenza A viruses undergo frequent changes in their surface antigens, whereas B changes less frequently. The immunity following infection by one strain may not fully protect one against subsequent antigenic variants. Therefore, new vaccines against influenza must be designed each year to match the circulating strains that are most likely to cause the next epidemic. Thus, a single dose of inactivated vaccine should be given annually before the influenza season starts.

Route of vaccination and adverse reactions

The vaccines are given by deep subcutaneous or intramuscular injection. 15-20% of those receiving a vaccine may develop local reactions lasting for 1 to 2 days. Very few may have transient systemic reactions such as fever, malaise and myalgias within 6-12 hours of vaccination.

Contraindication

Moderate to severe acute illness is a contraindication to influenza vaccination and the person could only received vaccination when symptoms subsided. Also, influenza vaccination would not interfere with other vaccines given at the same time. However, it should not be given to children aged under 6 months, and those between 6-35 months should only receive half (0.25ml/dose) of the adult vaccine dose (0.5ml/dose). Also, children aged under 8 years old who have not previously been vaccinated, should be given a second dose after an interval of at least 4 weeks.

Vaccination in UHS

UHS of CUHK offers an Influenza Vaccination Programme at cost $75 per dose. The current Inactive Influenza Vaccine (both Flura RIX from GSK and Vaxigrip from Aventis) contain the strains of A/New Caledonia/20/99 (H1N1)-like virus, A/Wisconsin/67/2005 (H3N2)-like virus and B/Malaysia/2506/2004-like virus, which is recommended by the WHO for the Northern Hemisphere in 2006. Vaccination programmes are organized monthly during high risk period. Priority will be given to high-risk groups; other staff, dependants and students can also join the programme.

Treatment

Those infected should take adequate rest, drink plenty of fluid, observe personal hygiene (especially washing hands frequently) so as to increase body defense to prevent the virus from spreading.

For most people, only symptomatic treatment is required since the person’s body will eliminate the virus within days.

Antibiotics cannot attack the virus while antiviral drugs for influenza may be indicated for some patients. However, they are not a substitute for vaccination and patients should be aware of the possible side effects of these drugs and the possibility of the virus developing resistance to the drugs.

In severe cases, admission to hospital, intensive care, prophylactic antibiotic therapy and breathing support may be required.

Current Situation in Hong Kong

According to the latest report from the WHO (released on 22 Mar 2006), human influenza activity remained low in most parts of the world. Only HKSAR and Japan have reported a high level of influenza A/H3N2. Influenza activity continued to increase in week 9-10 where a number of outbreaks in schools were reported and most of  isolates were identified as influenza A/H3N2 viruses.

Avian influenza, or the “bird flu”, is a worldwide, contagious disease of animals caused by a large group of different influenza viruses that primarily affect birds, and rarely, causes infection on pigs and humans.

The virus

Avian H5N1, a type of Influenza A, is a strain with pandemic potential, since it might ultimately adapt into a strain that is contagious among humans. Its outbreaks in birds are of the greatest concern for human health. It is therefore important to ascertain the strains in all outbreaks.

Signs and symptoms

It is more likely to result in high fever (usually ?38??) and influenza-like symptoms such as chest infection and failure in the lower respiratory tract. Watery diarrhoea without blood appears to be more common in Avian H5N1 than in normal seasonal influenza. Multi-organ failure and even death may result.

High-risk groups

In addition to the high-risk group of influenza mentioned above, people who have contact with poultry are also at high risk.

Mode of Transmission and Incubation period

Human case of Avian Flu is transmitted from direct contact with infected live birds to man, or surfaces and objects contaminated by their faeces. Transmission between humans is very ineffective.

According to WHO (released in Feb 2006), the incubation period for Avian H5N1 may be longer than that for normal seasonal influenza, which is around two to eight days and possibly as long as 17 days.

Diagnosis

Confirmation of diagnosis will depend on laboratory tests on clinical samples from the patient.

Prevention

• Rapid culling of all infected or exposed birds. This is the most important and can be achieved by proper disposal of carcasses and the quarantining and vigorous disinfection of farms.
• Avoid touching live birds and poultry and their droppings. Wash hands thoroughly with liquid soap if you have been in contact.
• Poultry and eggs should be thoroughly cooked (70oC in all parts of the food) since the virus is sensitive to heat.
• Consult doctors and inform him/her your recent travel history immediately if you feel unwell after traveling outside Hong Kong.
• Follow the general advice under the section on Influenza Prevention above.

Influenza vaccination

Vaccine is not yet available. Influenza vaccination does not protect humans from H5N1 infection, but does minimize the risk of co-infection and genetic reassortment of human and avian influenza viruses in humans.

Treatment

Avian H5N1 is generally more severe than ordinary influenza, and many patients require hospitalization. Some anti-viral infection drugs may be effective in treating the condition. However, their effectiveness have yet to be confirmed and therefore should be used under the doctor’s instructions.

Current Situation in the world and Hong Kong

Outbreaks of Avain Flu in chickens began in south-east Asia in mid-2003 and has now spread to a few parts of Europe. To date, 9 Asian countries have reported outbreaks, but Japan, the Republic of Korea, and Malaysia have controlled their outbreaks and are now considered free of the disease. Vietnam has been the most severely affected country. According to WHO, currently, the risk of pandemic influenza is serious.

The first human case was identified in 1997 (18 cases with six deaths) in Hong Kong, and later in 2003 (2 cases with 1 death in Hong Kong). According to WHO (released on 14 Aug 2006), a total of 21 cases of human infection with H5N1 avian influenza virus have been confined, of which 14 have been fatal.

Hong Kong has an effective surveillance system for influenza in birds and humans. The Department of Health has been closely monitoring the situation (http://www.info.gov.hk/info/flu/eng/index.htm) and has adopted appropriate preventive measures to guard against the disease.

Advice to International Travelers

Despite outbreaks of H5N1 Avian Flu infection and human cases are being reported, the WHO does not recommend any restrictions on travel to any country.

However, preventive control measures mentioned above should be implemented.

3. Guidelines on Avian Flu Prevention

• Avoid touching live birds or poultry or their droppings.
• If you have contact with live birds or poultry, wash your hands immediately with liquid soap and water.
• Cook poultry and eggs thoroughly before eating.
• If you have flu symptoms, consult a doctor and wear a mask to prevent spreading the disease.
• If you are sick after returning from a country that reports an avian flu outbreak, consult your doctor and tell him/her about your travel history as soon as possible.

4. Case definitions for Avian Flu

Possible Case of Influenza A (H5N1):

• Person with acute respiratory illness, characterized by fever (temperature >38oC) and cough and/or sore throat, AND EITHER
• Contact with a confirmed case of Influenza A (H5N1) during the infectious period, OR
• Recent (less than 1 week) visit to a poultry farm in an area known to have outbreaks of highly pathogenic avian influenza (HPAI), OR
• Worked in a laboratory that is processing samples from persons or animals that are suspected from HPAI infection

Probable Case of Influenza A (H5N1):

• Possible case, AND
• Limited laboratory evidence for Influenza A (H5N1) (such as IFA + using H5 monoclonal antibodies), OR
• No evidence for another cause of disease

Confirmed Case of Influenza A (H5N1):

• Positive viral culture for Influenza A (H5N1), OR
• Positive PCR for Inluenza (H5), OR
• A 4-fold rise in H-5 specific antibody titer