Influenza: Information for Health Professionals

8th October 2004

Note: The advice contained in this document will be updated as new information comes to hand.

Key Points

• Influenza is distinguished from the common cold principally by the sudden onset of symptoms, high fever and predominant systemic symptoms.
• Complications from influenza are most common in the elderly and those with chronic medical conditions.
• Influenza vaccination is the best protection against influenza particularly for those in high-risk groups and health care workers
• Patients presenting with an influenza-like illness, particularly those who are in a high-risk group or require hospitalisation, should have appropriate respiratory specimens sent for laboratory diagnosis of influenza.
• Antiviral drugs may be used to treat patients with severe influenza-like illness, particularly those in high-risk categories, but need to be started within 48 hours of onset of symptoms in order to be effective.

What is influenza?
There are three types of influenza virus: influenza A and influenza B cause the majority of infections. The third type, influenza C, is rarely reported as a cause of human illness. 

What are the symptoms?
Influenza is characterised by sudden onset of symptoms with patients often recalling the exact hour the fever commenced. The symptoms include a temperature of 38ºC or more with a dry cough, headache, sore muscles and sore throat. Cough is often severe and protracted, but otherwise the disease is self-limiting and recovery is in 2-7 days. Long-term sequelae that can occur include depression and fatigue (asthenia) that can last weeks.

The current case definition for influenza-like illness (ILI), as used in the HPSC/ICGP/NVRL influenza sentinel surveillance system is:

• Sudden onset of symptoms with a temperature of 38° C or more, in the absence of any other disease, with at least two of the following:
  • Dry cough
  • Headache
  • Sore muscles
  • Sore throat.

Is it flu or the common cold?
It can be difficult at times to distinguish between the common cold and flu. The main difference is that the symptoms of influenza come on rapidly and are typically accompanied by muscle aches and a fever. The common cold has a more insidious onset and is associated with a runny nose, sneezing, and blocked nasal passages. Please see table below.

The symptoms of influenza in children are generally similar to those of adults. However, symptoms in infants may be less specific and include diarrhoea and vomiting. Children may also present with otitis media.

What are the complications from influenza?
The most frequent complication is pneumonia, most commonly secondary bacterial pneumonia. Primary influenza viral pneumonia is an uncommon complication but is associated with a high mortality. Other complications include worsening of pre-existing chronic medical conditions such as chronic bronchitis or chronic heart failure. Reye's Syndrome is a particular syndrome that almost exclusively occurs in children, primarily in association with influenza B infection and presents with severe vomiting, confusion and coma.

Death is reported in 0.5 - 1 per 1000 cases of influenza. The majority of deaths occur in those over the age of 65. Even in winters when the incidence of influenza is low, 3,000 - 4,000 excess deaths may be attributable to influenza in the United Kingdom.

How does influenza spread?
The virus multiplies in the nose and airway passages and usually spreads by aerosol droplet spray. It is highly infectious and can survive on worktops especially in low temperatures and in low humidity. The incubation period (delay between infection and appearance of symptoms) is short typically 1 - 3 days. A person can spread the virus by sneezing or coughing from 1 - 2 days before the onset of symptoms and continue to be infective for a further 3 - 5 days. This however may be prolonged to a week in children.

What advice should be given to a symptomatic person to limit the spread of influenza?
As the virus can spread through sneezing, coughing or contaminated hands or surfaces, ensuring good hygiene practices will help. Symptomatic persons should cover their mouth and nose when sneezing or coughing, ideally with a disposable tissue. They should wash their hands frequently, particularly after coughing or sneezing, using soap and water or and alcohol-based hand disinfectant. Health care workers should pay particular attention to hand hygiene, regardless of whether or not they are symptomatic.

Persons with influenza should limit contact with other people as much as possible. They should be advised to stay at home for at least five days after the onset of symptoms. It is particularly important that health care workers avoid any patient contact for at least five days after the onset of symptoms.

What precautions can be taken to prevent influenza?
Annual vaccination remains the best protection against influenza, especially in people who are at high risk of complications from influenza. The vaccine needs to be given annually to cover the variation in circulating influenza strains that occurs each year.

What investigations should be done for influenza?
Every effort should be made to confirm a diagnosis of influenza and to rule out other respiratory viruses, particularly in hospitalised patients and those for whom antiviral therapy is being considered. It is particularly important to rule out RSV infection in children, as this can be difficult to distinguish clinically from influenza infection.
Influenza virus can be grown in cell culture from a variety of clinical specimens and influenza antibodies can be detected by serology. However the best diagnostic test is detection of viral RNA in respiratory specimens using PCR. The PCR test for influenza, currently employed by the National Virus Reference Laboratory (NVRL), can also detect RSV in respiratory specimens.

The best specimen to take for influenza diagnosis is a Nasopharyngeal aspirate (NPA), particularly in younger children: 1-2mls should be suctioned from each nostril and placed in viral transport medium.

If an NPA is not available a nasal swab, placed in viral transport medium, may be used, though the diagnostic yield from such specimens may be less than with an NPA. Commercial viral swabs, which include viral transport medium, may be used.

Paired serum specimens, taken 2-4 weeks apart, should also be sent for influenza serology.

Advice on diagnosis of influenza, including details of specimens to be taken, should be sought from your local microbiologist, who will arrange referral of specimens to NVRL.

What can I take for influenza?
If influenza or influenza-like illness has been diagnosed, often the best treatment is to stay indoors, keep warm and drink plenty of liquids. Simple painkillers such as paracetamol may help relieve headache or muscle pains. Note: Aspirin should NOT be given to children under the age of 16 years.

Antibiotics have no effect on the influenza virus and are only rarely required (e.g. if a person develops influenza related complications such as a bacterial pneumonia).

What is the composition of the Northern Hemisphere influenza vaccine for the 2004/2005 influenza season?
The WHO has published its recommendations on the composition of influenza vaccines for use in the 2004-2005 Northern Hemisphere influenza season.

• A/New Caledonia/20/99(H1N1)-like virus
• ·an A/Fujian/411/2002(H3N2)-like virusa
• a B/Shanghai/361/2002-like virusb

a The currently used vaccine virus is A/Wyoming/3/2003. A /Kumamoto/102/2002 is also available as a vaccine virus.
b Candidate vaccine viruses include B/Shanghai/361/2002 and B/Jilin/20/2003, which is a B/Shanghai/361/2002-like

Who should get the vaccine?
There are guidelines set out by the Royal College of Physicians Immunisation Advisory Committee. Two groups are targeted:
1) Any individual over the age of six months of age who is at risk of influenza related complications
2) Those at increased risk of transmitting influenza to a person of high risk for influenza complications.

*Detailed information on the influenza vaccine for health care workers is available here on the HPSC website.

Why is the vaccine not given to everyone?
For the majority of people flu is not life threatening, however unpleasant it may be. A bout of flu offers long-term protection against the same and closely related strains of influenza. Children aged less than nine years who receive the vaccine for the first time require two doses, four to six weeks apart, making vaccination in this age group more problematic.
 
It is the "at risk" groups who benefit most from vaccination. The vaccine should therefore be targeted at those most in need and for whom it will be most effective.

What antiviral drugs are available?
There are currently four antiviral drugs that can shorten the course of infection if given early in the disease and provide short-term protection against influenza: amantadine, rimantadine, zanamivir and oseltamivir. Of these only zanamivir (trade name Relenza) and oseltamivir (trade name Tamiflu) are currently licensed in Ireland.
The UK National Institute for Clinical Excellence (NICE) do not recommend the use of amantadine for the treatment of influenza A. Although amantadine (Symmetrel) is licensed in Ireland, it is not licensed for treatment of influenza. Rimantadine is not licensed in Ireland.

Oseltamivir and zanamivir reduce replication of influenza A and B viruses by inhibiting viral neuraminidase. They are licensed for the treatment of influenza within 48 hours of the first symptoms. In otherwise healthy individuals they reduce the duration of symptoms by about 1/1.5 days. The effect of oseltamivir or zanamivir on hospitalisation or on mortality is not clear in those at risk of serious complications from influenza. Oseltamivir is also licensed for prophylaxis when used within 48 hours of exposure to influenza and when influenza is circulating in the community.

NICE guidance (oseltamivir, zanamivir, and amantadine for treatment of influenza)
NICE has recommended (February 2003) that antiviral drugs are not a substitute for vaccination, which remains the most effective way of preventing illness from influenza. When influenza A or influenza B is circulating in the community:

• amantadine is not recommended for the treatment of influenza;
• oseltamivir or zanamivir are not recommended for the treatment of otherwise healthy individuals with influenza;
• oseltamivir and zanamivir are recommended (in accordance with product licensing) to treat at-risk adults who can start treatment within 48 hours of the onset of symptoms; oseltamivir is recommended for at-risk children who can start treatment within 48 hours of the onset of symptoms;

At-risk patients are defined as those aged over 65 years or those who have one or more of the following conditions:

• chronic respiratory disease (including chronic obstructive pulmonary disease and asthma), though zanamivir should be used with caution in such patients (see product);
• significant cardiovascular disease (excluding hypertension);
• chronic renal disease;
• immunosuppression; <
• diabetes mellitus.

The usual adult dose of oseltamivir (Tamiflu) is 75mg BD for five days, but should be reduced in the setting of severe renal impairment. The paediatric dose is based upon weight:

• Less than 15kg: 30mg BD
• 15-23 kg: 45mg BD
• 23-40kg: 60mg BD
• Over 13yrs or over 40Kg: same as adult.

Note that the paediatric formulation of oseltamivir (Tamiflu) is not currently available in Ireland. The manufacturers suggest that the adult capsule can be broken in half and half of the enclosed powder dissolved in orange juice to be used for treating children. This is not a licensed use of the product and is not supported by clinical trial data. In the absence of a paediatric formulation, however, individual clinicians should carry out a clinical risk assessment before deciding on therapy for at risk children with an influenza-like illness. 

Zanamivir (Relenza) is given by inhalation and the recommended dose is two inhalations (2 x5mg) twice daily for five days, providing a total daily inhaled dose of 20mg. Supplies of zanamivir (Relenza) in Ireland may be limited. The drug should be used with caution in people with asthma or chronic pulmonary disease, due to an increased risk of bronchospasm. 

If a household or other close contact of an "at risk" person presents with symptoms of influenza, the "at risk" individual should be informed of the increased risk of getting influenza. They should be asked to consult their GP as soon as possible if they develop symptoms consistent with influenza, to facilitate early initiation of antiviral therapy.

Details of the NICE recommendations on use of antiviral agents for influenza prophylaxis 

Details of the NICE recommendations on use of antiviral agents for influenza therapy

For further information on influenza see the following websites:
Health Protection Surveillance Centre

World Health Organisation

Health Protection Agency (UK)

Centers for Disease Control and Prevention

European Influenza Surveillance Scheme:

Note: This guidance was developed by an ad-hoc advisory group on influenza, convened in response to the recent increase in influenza-like illness. The members of the advisory group are:

• Dr. Karina Butler (Our Lady's Hospital for Sick Children, Crumlin)
• Dr. Eibhlin Connolly (Department of Health and Children)
• Dr. Robert Cunney (Health Protection Surveillance Centre)
• Dr. Joan Gilvarry (Irish Medicines Board)
• Prof. William Hall (National Virus Reference Laboratory)
• Dr. Marie Laffoy (HSE Eastern Region)
• Dr. Dermot Nolan (Irish College of General Practitioners)
• Dr. Joan O'Donnell (Health Protection Surveillance Centre)
• Dr. Darina O'Flanagan (chair) (Health Protection Surveillance Centre)