Influenza

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INFLUENZA

Influenza is an acute respiratory illness caused by infection with influenza type A or B virus. It typically occurs in outbreaks over a five-to six-week period each winter. Each year, hundreds of thousands of excess hospitalizations, tens of thousands of excess deaths, and billions of dollars in health care costs can be attributed to influenza and its complications. Attack rates can be as high as 10 to 40 percent in the community, and examination of influenza epidemic curves typically reveals a bimodal pattern, with attack rates highest in the young and morbidity and mortality highest in the elderly population. In most studies, elderly persons with chronic respiratory conditions account for up to 80 percent of patients with such serious complications as hospitalization and death.

Influenza can be a particularly difficult problem for people who live in long-term care facilities (LTCFs), where case fatality rates during outbreaks often exceed 5 percent. Up to 22 percent of residents that acquire influenza will develop complications of infection severe enough to result in hospitalization. Once influenza is introduced into a LTCF by staff and visitors, these relatively closed communities are an ideal setting for the rapid spread of influenza by droplet transmission. Attack rates among residents can exceed 40 percent.

Clinical findings

Influenza is typically characterized by the abrupt onset of fever, chills, headaches, severe myalgias (muscle pains), malaise, and loss of appetite. These are evident after an incubation period of one to two days. In the first three days of illness, headache and muscle pain are usually the most bothersome symptoms, with the severity of these complaints reflecting the magnitude of the fever. Dry cough, severe sore throat, and nasal obstruction and discharge are usually also present, although they may be overshadowed by the systemic complaints. The fever typically resolves after approximately three days, but the cough, sore throat, and hoarseness may persist for three to four days after the fever resolves. It is important to remember that in frail older adults disease presentation can be atypical. For example, some individuals might present only with fever, lack of energy, or confusion, and without any evidence of respiratory illness. Influenza should be considered in any illness characterized by fever in an elderly person during influenza season.

Without complications, influenza is a self-limited illness lasting five to eight days. Elderly patients and patients with high-risk medical conditions, including chronic lung or heart disease, kidney disease, problems with the immune system, cancer, or other chronic medical problems are at risk for developing complications from influenza. Pneumonia caused by the influenza virus itself and secondary bacterial pneumonia are the most common and serious complications of influenza. Patients with influenza pneumonia, a complication which is fortunately quite rare, will present with typical signs and symptoms of influenza but go on to develop severe cough, shortness of breath, and cyanosis. Chest X-rays will usually show bilateral findings most consistent with adult respiratory distress syndrome, and gram stains of sputum will not identify a bacterial pathogen. Death, due to diffuse hemorrhagic pneumonia, is high even with prompt antiviral therapy.

Secondary bacterial pneumonia is indistinguishable from community-acquired pneumonia in the absence of influenza, except that it typically occurs in elderly patients or patients with chronic heart or lung problems after recovery from a classic influenza illness. Patients will usually describe a recurrence of fever, cough, and sputum production four to fourteen days after their initial recovery from influenza. Physical examination and chest X-ray usually reveal a focal area of lung infection. Microbiological examination of the sputum often shows bacteria such as Streptococcus pneumoniae or Haemophilus influenzae. Treatment of community-acquired pneumonia as a secondary complication of influenza infection is not different than in any other setting, and requires antibiotic drugs.

Diagnosis

Influenza virus can be readily isolated from nasal swabs, throat swabs, nasal washes, and sometimes sputum. A throat swab alone is less sensitive than nasal or throat washes, and thus washes are preferred. Specimens should be placed into containers of viral transport medium and transported to the laboratory for viral culture. Two-thirds of positive cultures will be detected within seventy-two hours, with the remainder within five to seven days. However, particularly for influenza detection in long-term care facilities, faster methods of detection are needed. A variety of rapid detection methods for influenza virus exist that detect viral antigens by immunofluorescence or ELISA in as little as one hour, with reasonable sensitivity and specificity under optimal conditions. At present though, viral culture remains the gold standard for diagnosis of influenza infection.

Treatment

In otherwise healthy children and adults with uncomplicated influenza infection, antiviral therapy is not generally warranted. Bed rest, adequate fluid intake, and treatment with analgesics, cough suppressants, and decongestants may improve symptoms. In patients at significant risk for the development of complications of influenza, or in those with influenza pneumonia, the use of antiviral medications may decrease morbidity and mortality. Until recently, therapy for influenza typically involved the use of amantadine or rimantadine, antiviral drugs active against influenza A. Most studies examining the efficacy of these drugs have shown a reduction in clinical symptom scores, a faster resolution of fever, and a decrease in the level and duration of infectivity. Most authorities support the use of amantadine in the treatment of complicated influenza A virus infection, even late in the course of illness. Treatment with antiviral medications is also generally recommended for outbreaks of influenza A virus infection in LTCFs, although whether these drugs prevent illness, relieve symptoms, or reduce the duration of illness or complications in this setting is not clear.

These drugs can lead to complications. Confusion, delerium, seizures, falls, insomnia, or fractures occur in 22 to 47 percent of residents of LTCFs treated with amantidine, and drug resistance develops readily. Side effects can be reduced in the elderly by reducing the dose of amantadine to 100 mg or less daily in the presence of renal insufficiency. Central nervous system side effects are less problematic with rimantadine than with amantadine.

The neuraminidase inhibitors are a new class of antiviral medications with activity against both influenza A and B virus. These agents, although expensive, offer a much better side-effect profile and are better tolerated in the elderly than amantadine. Although resistance to these agents has been reported, it is not yet a significant problem. The role of these agents in the prevention and treatment of influenza infections in the elderly has not yet been established, but there is mounting evidence to suggest that they may play a key role in the management of influenza in LTCFs in the near future.

Prevention

Influenza vaccination represents the safest, most cost-effective means of prevention of morbidity and mortality from influenza virus. Current guidelines recommend influenza vaccine yearly in all individuals over age sixty-five, all residents of LTCFs, children or adults with chronic pulmonary or cardiovascular illness, children requiring chronic aspirin therapy, and women in the second or third trimester of pregnancy during influenza season. Yearly influenza vaccine is also recommended in health care workers, employees of LTCFs who come in contact with patients, and home care providers or others who have household contact with high-risk individuals.

At present, an inactivated vaccine directed at three viruses (influenza A H1N1, H3N2, and influenza B) is currently used. This vaccine can reduce the incidence of confirmed influenza, influenza-like illness, all respiratory infections, exacerbations of cardiopulmonary disease, hospitalization, and death in both community-dwelling elderly persons and in residents of LTCFs. Although the vaccine has only 30 to 40 percent efficacy in preventing influenza in residents of LTCFs, severe illness, hospitalization, and death are significantly reduced. High vaccination rates among residents of a LTCF significantly reduce the chances of an outbreak occurring in that facility, and should an outbreak occur, vaccination will decrease hospitalizations by 50 to 60 percent and mortality by as much as 80 percent. In order to maximize the effectiveness of the vaccine in the prevention of influenza-associated morbidity and mortality in residents of LTCFs, it is critical that high staff vaccine rates be maintained in hopes of reducing and delaying introduction of influenza into these facilities. A newly developed but not yet licensed cold-adapted, live, attenuated, trivalent, intranasal influenza vaccine has been shown to increase serum, mucosal, and cell-mediated immunity when given in combination with the currently available intramuscular vaccine.

Shelly McNeil

See also Lung, Aging; Pneumonia.

BIBLIOGRAPHY

Bradley, S. F., et al. "Prevention of Influenza in Long-Term Care Facilities." Infection Control Hospital Epidemiology 20 (1999): 629–637.

Libow, L. S.; Neufeld, R. R.; Olson, E.; Breuer, B.; and Starer, P. "Sequential Outbreak of Influenza A and B in a Nursing Home: Efficacy of Vaccine and Amantidine." Journal of the American Geriatric Society 44 (1996): 1153–1157.

"Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices." Morbidity and Mortality Weekly Report 47 (1998): 1–16.

Treanor, J. J. "Influenza Virus." In Principles and Practices of Infectious Diseases, 5th ed. Edited by G. L. Mandell, J. E. Bennett, and R. Dolin. New York: Churchill Livingstone, 2000. Pages 1823–1849.