This webpage has been archived since 7 March 2007, and is no longer being maintained or updated. For updated information on influenza, please refer to Committee on Health Promotion and Protection website.
Talks
Prof Paul Chan, Department of Microbiology, Faculty of Medicine [
Dr T F Lo, University Health Service [PDF]
Mr S K Lam, University Safety & Environment Office [PDF]
Avian Flu Forum (Feb 2004)
Prof Paul Chan, Department of Microbiology, Faculty of Medicine [PDF]
Information
The Virus
Transmission
Diagnosis
Prevention
Influenza Vaccination
Treatment
Current Situation of Influenza in Hong Kong
Prevention of Avian Flu
Treatment of Avian Flu
Use of Antivirals for Pandemic InfluenzaWhy Avian Flu is a Major Public Health Concern
Current Situation
Current Situation of Avian Flu in Hong Kong
Advice to International Travellers
_______________________________________________________________________________
Influenza is caused by a virus that attacks mainly the upper respiratory tract ?the nose, throat and bronchi and rarely also the lungs. The infection usually lasts for about a week. It is characterized by sudden onset of high fever, muscle pain, headache and severe malaise, non-productive cough, sore throat, and runny nose. Most people recover within 1 to 2 weeks. In 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.
The Virus:
Influenza viruses are defined by 2 different antigens on their surface, called Haemagglutinin (H) and neuraminidase (N).
The currently circulating influenza viruses that cause human disease are divided into 2 groups: A and B. Influenza A has 2 subtypes that are important for human: A(H3N2) and A(H1N1). The former causes higher morbidity and mortality.
The virus is easily passed from person to person through the air by droplets and small particles excreted when infected individuals cough or sneeze. The virus enters the body through the nose or throat. It then takes between one and four days for the person to develop symptoms (incubation period).
Influenza patients can be infectious from the day before they develop symptoms until 7 days afterwards.
Influenza spreads very quickly among in the community especially in crowded circumstances. Cold and dry weather enables the virus to survive longer outside the body than in other conditions.
The peak
season in
Mild respiratory illness caused by influenza is difficult to distinguish from illness caused by other respiratory pathogens on the basis of symptoms alone e.g. common cold.
Unless when an outbreak has occurred in the community, laboratory confirmation will be required between the annual influenza epidemics.
The best protection against Influenza is by building good body resistance. This can be achieved through a balanced diet, regular exercise, adequate rest, reducing stress and no smoking. If you have fever and/or symptoms of respiratory tract infection, better avoid crowded public places where the ventilation is not good. Your should also consult a doctor and wear a mask to prevent spread of the disease. Frequent hand washing is also an important practice.
Influenza virus types A and B are both common causes of acute respiratory illnesses. Influenza A viruses are the principal cause of larger epidemics including worldwide pandemics; whereas influenza B infections are often limited to localized outbreaks.
Influenza occurs in all age groups, with the highest infection rate among children. However, severe morbidity and mortality from the disease are more common among those aged over 65 years, and in specific high-risk groups. Those included in the high-risk groups are patients with pulmonary or cardiovascular illness, metabolic diseases including Diabetes Mellitus and renal dysfunctions, and various types of immuno-suppression. Residents of long-term care facilities are also at a higher risk of acquiring influenza infection. In addition to the high-risk groups, vaccination is generally recommended to health care workers in regular contact with patients and household contacts of high-risk persons.
Influenza A viruses undergo frequent changes in their surface antigens, whereas type B influenza viruses change less frequently. The immunity following infection by one strain may not protect fully against subsequent antigenic variants. As a consequence, new vaccines against influenza must be designed each year to match the circulating strains that are most likely to cause the next epidemic. To this end, WHO makes recommendations twice annually the influenza vaccine compositions to be used for the southern and northern hemisphere. Currently, two subtypes of influenza A (A/H1N1 and A/H3N2) virus as well as influenza B virus are included in the vaccine.
The main purpose of influenza vaccination is to avoid severe influenza and its complications. Protection against influenza is thought to be mainly conferred by serum antibodies. The antibodies are specific to variants within a given subtype and protection may be reduced or lost as a consequence of antigenic change in new infecting strains.
Internationally-licensed influenza vaccines have proved to be efficacious and safe. Although antiviral drugs are available, the emergence of resistant viral mutants to the drugs, the occasional side effects, drug costs and limited availability during major outbreaks highlight the role of vaccination as the primary preventive measure against influenza.
Most inactivated influenza vaccines are given by injection in the deltoid muscle (or thigh in the case of infants). Generally a single dose of inactivated vaccine annually is appropriate.
15%-20% of those who received vaccine may have local reactions lasting for 1 to 2 days. There may also be transient systemic reactions such as fever, malaise and myalgias within 6-12 hours of the vaccination.
Moderate to severe acute illness is a contraindication to influenza vaccination until symptoms have decreased.
If influenza vaccination of children is required, for example as a consequence of predisposing conditions, the vaccine will not interfere with diphtheria-pertussis-tetanus (DPT) or other childhood vaccines, possibly due at the same time. However, influenza should not be given to children aged under 6 months, and those aged 6-35 months should only receive half the adult vaccine dose.
Influenza vaccination is also recommended as a measure for better surveillance of SARS outbreaks and for prevention of emergence of Human Avian Influenza.
In summary, please note the following facts for the influenza vaccination programme
1. Type of vaccine: inactive, non-infectious viral
2. Number of doses: one, given by the subcutaneous or intramuschular doute
3. Schedule: Once a year at November, before the influenza season starts (February and March)
4. Booster: Boosters are unhelpful as the composition of the wild virus changes each year. One dose of the appropriate vaccine strains is needed annually
5. Contraindications: Severe hypersensitivity to egg or to previous dose
6. Adverse reactions: Local pain or tenderness, fever, malaise
7. Special Precaution: None.
UHS of CUHK offers an Influenza Vaccination Programme at cost at $60 per dose. The Inactive Influenza Vaccine* Flura RIX from GSK and Vaxigrip from Aventis both contains the strains of A/New Caledonia/20/99 (H1N1)-like virus, A/California/7/2004 (H3N2)-like virus and B/Shanghia/361/2002-like virus. The vaccine complies with the WHO recommendation for Southern and Northern Hemisphere 2005. This vaccination programme has been organised on a monthly basis since September 2005 for all the high-risk groups, all staff, dependants and students.
People with influenza should have adequate rest and sleep and drink plenty of fluid. Patients should also observe personal hygiene and wash hands frequently to prevent spreading the virus.
For most people influenza is an upper respiratory tract infection that lasts several days and requires symptomatic treatment only. Within days, the person’s body will eliminate the virus. Antibiotics cannot attack the virus.
Antiviral drugs for influenza may be indicated for some patients. However, they are not a substitute for vaccination. 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 influenza, admission to hospital, intensive care, antibiotic therapy to prevent secondary infection and breathing support may be required.
Current Situation of Influenza In
The latest
report from the Department of Health is that, (for the second half of January
2004) influenza activity in
Avian Flu, or Bird Flu, is a contagious disease of animals caused by viruses that normally infect only birds and, less commonly, pigs. While all bird species are thought to be susceptible to infection, domestic poultry flocks are especially vulnerable to infections that can rapidly reach epidemic porportions.
Avian Flu
(H5N1) is one type of Influenza A. It is
known previously to infect birds only and is a disease first identified in
Human cases of Avian Flu is transmitted from infected live birds to man. Transmission between humans is very inefficient.
Avian Flu has similar clinical presentation as other influenza viruses. However, it is more likely to result in high fever, chest infection, respiratory failure, multi-organ failure, and even death.
Outbreaks of Avian Flu in chickens have recently been reported in some 10 Asian countries. Cases of human infection have also been reported.
The most important control measures are rapid culling of all infected or exposed birds, proper disposal of carcasses, ant the quarantining and vigorous disinfection of farms.
For human infection, follow the general advice under the section on Influenza Prevention above.
Droppings of infected live birds and poultry may carry the Avian Flu virus. You should avoid touching live birds and poultry and their droppings. If you have been in contact with live birds and poultry, wash hands thoroughly with liquid soap each time after touching it or after cleaning its droppings.
The virus is killed by heat and common disinfectants. Poultry should be thoroughly cooked before eating.
When
traveling outside
Vaccine for Avian Flu is not available. Influenza vaccination will not protect humans from infection with avian H5N1. But it minimizes the risk of co-infection and genetic reassortment of human and avian influenza viruses in humans.
Avian Flu H5N1 is generally more severe than an ordinary influenza, and many patients require hospital care. Some anti-Viral Infection drugs may be effective in treating the condition. However, their effectiveness is still being confirmed and they should be used carefully following doctor’s instructions as they may cause adverse side effects.
Why Avian Flu is a Major Public Health Concern:
Since mid-December 2003, a growing number of Asian countries have reported outbreaks of highly pathogenic avian flu in chickens and ducks. The rapid spread is unprecedented historically.
Particularly alarming, in terms of risks for human health, is the detection of a highly pathogenic strain, known as “H5N1? as the cause of most of the outbreaks. H5N1 has jumped the species barrier, causing severe disease in humans, on 2 occasions in the recent past and is now doing so again.
Experts cautioned the possibility of another influenza pandemic in humans. This could be the outcome of a simultaneous infection of human and avian influenza viruses giving rise to an exchange of genes in the virus. Few, if any, humans would have the natural immunity to the new subtype of the influenza virus. The current flu vaccine would no longer be effective. In other words, as the number of human infections with avian flu virus grows, the risk increases that a new virus subtype could emerge, triggering an influenza pandemic.
If the new virus contains sufficient human genes, transmission directly from one person to another can occur ?creating the condition for a pandemic.
WHO is currently of the view that there is still no evidence of an efficient human-to-human transmission.
H5N1
outbreaks in birds are of the greatest concern for human health. It is therefore to ascertain the strains in
all outbreaks. Experts advise that some
virus in
WHO has not issued any travel advisory against any countries or locations.
http://www.who.int/csr/disease/avian_influenza/en/index.html
http://www.who.int/csr/disease/avian_influenza/country/en/
Current
Situation of Avian Flu in
Please refer to the following websites of the Centre for Health Protection, Department of Health, HKSAR:
http://www.info.gov.hk/info/flu/eng/index.htm
http://www.info.gov.hk/info/flu/eng/global.htm
http://www.chp.gov.hk/epidemiology.asp?lang=en&id=332&pid=134&ppid=29
Advice to International Travellers:
Despite that some country are currently experiencing outbreaks of
Avian Flu (H5N1) infection in poultry flocks, and that some have also reported
cases in humans, WHO does not at present recommend any restrictions on travel
to any country.
International travellers to areas experiencing
outbreaks of Avian Flu infection should avoid contact with live animal markets
and poultry farms. Large amounts of the virus are known to be excreted in the
droppings from infected birds. Please also refer to the set of guidelines on
this webpage.
Possible Case of Influenza A (H5N1):
l person with acute respiratory illness, characterized by fever (temperature >38oC) and cough and/or sore throat, AND EITHER
l contact with a confirmed case of Influenza A (H5N1) during the infectious period, OR
l recent (less than 1 week) visit to a poultry farm in an area known to have outbreaks of highly pathogenic avian influenza (HPAI), OR
l worked in a laboratory that is processing samples from persons or animals that are suspected from HPAI infection.
Probable Case of Influenza A (H5N1):
l possible case, AND
l limited laboratory evidence for Influenza A (H5N1) (such as IFA + using H5 monoclonal antibodies), OR
l no evidence for another cause of disease
Confirmed Case of Influenza A (H5N1):
l positive viral culture for Influenza A (H5N1), OR
l positive PCR for Influenza (H5), OR
l a 4-fold rise in H-5 specific antibody titer