Influenza: Prevention and Treatment

Covering the mouth and nose when coughing and sneezing, washing hands appropriately, and avoiding touching one's eyes and nose are the most effective preventive strategies to avoid infection.

Phenol/acetate sprays for household use have virucidal qualities.

Vaccines produced annually do not always prevent influenza and will not protect against emerging strains of avian influenza. However, annual vaccines help avert epidemics, because they reduce the risk of coinfection. The combination of 2 influenza virus infections in a single individual allows the sharing of genetic material, a process called reassortment, which can produce more virulent strains.

Exercise appears to improve vaccine response, particularly in the elderly. The efficacy of influenza vaccine is reduced in older people, partly because of the immunosenescence that occurs with aging.5 Moderate exercise (>20 minutes, 3 times/week) significantly improved antibody response to influenza vaccine in this population.^5,6

In older individuals, levels of perceived stress have been shown to affect certain immune responses to flu vaccine (eg, production of antibodies and interleukin-2).^5,7 A limited body of evidence suggests that stress-management interventions can produce significant increases in antibody titer after flu vaccination.⁸ However, further research is required before such interventions can be recommended universally.

Treatment

Influenza is a self-limited illness, except in high-risk individuals or when a highly pathogenic strain is involved. In general, symptoms can be prevented or reduced in duration with antivirals if started within 48 hours, although drugs are most effective when started within 24 hours of exposure or symptom development. It is not clear whether these drugs prevent complications or are effective in high-risk populations.⁹

The following antivirals may reduce symptoms and shorten the course of disease.

Amantadine and rimantadine (M2 ion channel blockers). These drugs are only effective against influenza A. Rimantadine may have fewer central nervous system side effects. Resistance may develop, and if one drug is ineffective, the other drug is also ineffective. The current H5N1 avian influenza is resistant to these drugs, as were most strains of influenza A in the 2005/2006 flu season. Sensitivity patterns should be known before prescribing these drugs.

Oseltamivir (Tamiflu) and zanamivir (Relenza). These neuraminidase inhibitors are generally effective for prevention and treatment of influenza A and B, but only oseltamivir is approved for prevention. Most H5N1 infections have been sensitive to oseltamivir, although resistance has been reported.¹⁰ Oseltamivir is generally well-tolerated, but zanamivir may cause respiratory side effects, including bronchospasm, in those with respiratory problems.

Probenecid. This gout medication, when taken simultaneously with one-half the normal oseltamivir dose may provide an effective serum concentration for influenza treatment, thus extending the supply of a potentially scarce medicine.¹¹ This is an off-label use of probenecid.

Acetaminophen, aspirin, and ibuprofen. These common medications may improve myalgias. Their use for mild fever is unnecessary. Aspirin should not be used in children with an acute viral illness, due to the risk of Reye's syndrome. When cold symptoms occur, only symptomatic treatment is beneficial (see Upper Respiratory Infection).

Complications of influenza include viral and/or bacterial pneumonia, myositis, rhabdomyolysis, Reye's syndrome, and toxic shock syndrome (when S. aureus combines with influenza B infection). All of these require specialized treatment.