Influenza is a serious health concern among elderly people. Each year in Canada, up to 75,000 people are admitted to hospital with influenza, and of these, the number of deaths has ranged from 1,500 to 6,700.^1,2 In particular, people over the age of 65 are at risk of developing complications of infection. It has been estimated that 90% of influenza-related deaths in Canada are of people in this age group, and half of these occur in long-term care facilities.^3,4 Institutionalized elderly are especially vulnerable because of their advanced age and underlying illnesses (high-risk conditions include chronic respiratory or cardiac disease, renal disease, diabetes and cancer), as well as their close mutual proximity with a range of caregivers. Of the three types of influenza virus (A, B, C), influenza A is responsible for the more severe illness and can lead to pneumonia, hospitalization and even death in the elderly and those with chronic illnesses.

The Canadian National Advisory Committee on Immunization (NACI) recommends annual influenza vaccination for all people over the age of 65 years,⁵ as well as for health care workers and personnel who have significant contact with people in high-risk groups. Immunization is more effective if given at least two weeks before the beginning of the active flu season (by mid-November), although the elderly should be advised to receive their vaccination earlier in October.

The effectiveness of influenza vaccine depends upon the age and immunocompetence of the recipient and how closely the vaccine matches the virus strain. With a good match, vaccination has been shown to prevent influenza in 70-90% of healthy adults and children, and is approximately 70% effective in preventing hospitalization for pneumonia and influenza among community-dwelling elderly. Studies of institutionalized elderly suggest vaccination is 50-60% effective in preventing hospitalization and pneumonia, and up to 85% effective in preventing death, even though efficacy in preventing the actual flu illness may be only 30-40% among the frail elderly.⁵ Furthermore, randomized controlled studies have found that health care staff vaccination reduces influenza-related morbidity and death among facility residents.⁶

Despite the influenza vaccination being recognized as the single most effective means of preventing or attenuating influenza for those at high risk, and NACI's ultimate goal to vaccinate at least 90% of all eligible people, only 70-91% of long-term care facility residents and 20-40% of adults and children with medical conditions receive vaccine annually. Studies of health care workers in hospitals and long-term care facilities have shown vaccination rates as low as 26%, ranging up to 61%.⁵ Many health care providers experience subclinical infection and thus continue to work, potentially transmitting infection to their patients. Low rates of utilization are due to both failure of the health care system to offer the vaccine, as well as fears about adverse reactions or skepticism of its efficacy or necessity. Health care providers have an important responsibility to help NACI reach its goals, as they often have great influence over whether or not a patient decides to be immunized. Furthermore, "in the absence of contraindications, refusal of health care workers to be immunized implies failure in their duty of care to their patients".⁵

Sources

1. Canadian Consensus Conference on Influenza. Can Commun Dis Rep 1993;19:136-47.
2. Health Canada, Population and Public Health Branch. Information Sheet on Influenza, November 2001.
3. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1999;48(RR-04):1-28.
4. Nicholson KG. Should staff in long-stay hospitals for elderly patients be vaccinated against influenza? Lancet 2000;355:83-4.
5. National Advisory Committee on Immunization. Statement of influenza vaccination for the 2002-2003 season. Can Comm Dis Rep 2002;28(ACS-5):1-17.
6. Carmen WF, Elder AG, Wallace LA, et al. Effects of influenza vaccination of health-care workers on mortality of elderly people in long-term care: a randomized controlled trial. Lancet 2000;355:93-7.

Katherine Sheehan
University of St. Andrews,
St Andrews, Scotland.

Michael Gordon, MD, MSc, FRCPC
Vice President of Medical Services,
Baycrest Centre for Geriatric Care,
Professor of Medicine,
University of Toronto,
Toronto, ON.

The infection control troops are preparing for battle, waiting for the declaration of war. Once again, it's nearly time for our annual fight against the influenza virus. This potential killer affects hundreds of thousands of Canadians each year, leading to the hospitalization of 75,000 and resulting in 6,700 deaths. Of those who die, 90% are over the age of 65 and about half are residents of long-term care facilities. Elderly residents are particularly vulnerable because of their advanced age, underlying illness, close quarters with other residents and extensive contact with many caregivers.

D'Arcy L. Little, MD, CCFP
Director of Medical Education
York Community Services, Toronto, ON

Introduction
Influenza, an acute respiratory illness, causes more adults to seek medical attention than any other respiratory infection. In Canada, influenza is a seasonal disease, causing annual epidemics that affect 10-20 percent of the population and result in approximately 4,000 deaths, 70,000 hospitalizations, and 1.5 million days of lost work.¹ The elderly (people aged 65 years and older), and those with chronic cardiopulmonary disorders, diabetes and other metabolic diseases, have an increased risk of developing influenza complications. Hospitalization rates among elderly patients increase markedly during major influenza epidemics, and 90% of the deaths attributed to influenza and pneumonia are observed in this population.²

Vaccination remains the most reliable means of preventing an influenza infection and the resultant morbidity and mortality. Despite the significance of influenza, efforts to vaccinate the elderly remain suboptimal. A large study conducted in the Netherlands revealed that healthy elderly people avoid influenza vaccination because they fear the side effects, and because they believe that their general health is good and that the benefits of vaccination are, therefore, minimal.

An 'Achilles Heel' in Viral Replication Helps Researchers Develop a Universal Cure for Influenza

Nadège Chéry, PhD

When influenza attacks, it may infect anyone, regardless of his or her age. But when influenza kills, it usually takes the lives of individuals, like the elderly, who are less able to fight back.² In Canada, 6000 deaths are attributable to influenza every year³ with the highest rate of mortality occurring among people over 65 years of age.² Thus, when it comes to older individuals, both early diagnosis, and prevention are imperative. Because the influenza virus continuously changes, strategies for the prevention of flu outbreaks, although thoughtfully planned, have had limited success. Recently, however, scientists have found a "weakness" in influenza's ability to escape traditional flu therapies. This discovery has set the stage for the design of new antiviral drugs which, potentially, may constitute a cure for the flu.

What is Influenza?
Influenza is a member of the Orthomyxoviridae family,1 and causes disease by infecting the epithelial cells that compose the lining of the respiratory tract. Influenza produces symptoms similar to other viruses which infect the respiratory tract. Flu outbreaks are common among elderly persons, particularly in nursing homes.⁴ Since the immune systems of elderly people in a nursing home may be compromised,⁵ their ability to fight an influenza infection can be severely undermined.

Vaccination Curtails Influenza Outbreaks, but Side Effects are Still Possible

Dr. Allison McGeer MSc, MD FRCPC
Director,
Infectious Control,
Mount Sinai Hospital,
Toronto, ON

Every year, approximately one in six Canadians are infected with influenza. Healthy adults infected with influenza miss, on average, 2-7 days of work, and have a 10-30% chance of being prescribed a course of antibiotics. Influenza causes approximately 20% of all cases of acute otitis media in children,¹ and is the most common single infectious cause of hospital admission in young children.^2-4 However, the greatest impact of influenza is seen in the elderly. Every year, nearly 1% of older adults with any chronic underlying illness require hospital admission due to influenza, and about 4000 die from influenza and its complications.⁵

Vaccination is the only effective method for the prevention of influenza. Annual vaccination is required because influenza viruses are able to mutate their antigenic coat continuously in order to evade the human immune system (see "Chasing Away the Flu Bug" on page 20 for a more detailed description of this process).

D'Arcy L. Little MD, CCFP
York Community Services, Toronto

Relenza (zanamivir), an orally-inhaled anti-viral medication effective against all known strains of the influenza virus, was approved by the Therapeutic Products Program of Health Canada on November 3, 1999.

Epidemiology
It is estimated that in Canada influenza affects between 10 to 15% of the population (between 3 and 5 million people) each year. The number of affected persons can be as high as 80% of nursing home residents. In addition, these infections result in about 75,000 hospitalizations and 7,000 deaths yearly.¹ In economic terms, flu-related costs to the Canadian economy during the 1997-98 flu season were estimated to be over $1 billion.²

The Mainstay of Treatment for Influenza
The influenza vaccine has been and remains the mainstay of prophylactic protection against influenza, and is recommended for elderly and high-risk patients, their household contacts, and health-care personnel. Under ideal circumstances, in healthy, young adults, vaccine effectiveness is in the range of 70-90%, with much lower effectiveness in the elderly (30-50%).³ For optimal results, it is recommended as a single 0.5 ml IM dose to be given from October through mid-November, although it can be given from September to the end of the influenza season.

Michele Kohli, BSc, MSc

The persistence of influenza in the North American population has not been completely explained by epidemiologists.¹ During the last influenza season (1997-98), there were 5,148 laboratory confirmed cases of influenza in Canada (see Table 1).² The elderly population, those aged 65 years and above, are particularly susceptible to this disease. Over 95% of the deaths caused by influenza occur in this age group, in part, because of the higher prevalence of congestive heart failure and lung disease.¹ Last year, the occurrence of influenza peaked between January and March.² When the prevalence of influenza is high in a population, patients presenting with a febrile respiratory illness along with symptoms such as myalgia, headache, sore throat and cough are often diagnosed as having influenza.¹ However, the gold standard for diagnosis is laboratory detection of the virus in nasopharyngeal swabs.¹ The genes of the influenza virus mutate frequently, causing the antigenic molecules of the virus to change, resulting in the emergence of new viral sub-types. This process is known as antigenic drift. When human and swine or avian strains of influenza A recombine, the resulting new subtypes can cause pandemics.