Influenza (Flu)

– An acute viral respiratory disease with clinical manifestations that often resemble a severe form of the common cold.

Causes and Incidence

Influenza is caused by orthomyxovirus types A, B, and C, which are spread by direct person-to-person contact or by airborne droplet spray. Flu generally occurs in the late fall and early winter and can reach epidemic proportions when a modified form of the virus emerges for which the population has no immunity. All age groups are susceptible, but the prevalence is highest in school-age children.

Disease Process

After a 48-hour incubation period, the virus penetrates the surface of the upper respiratory tract mucosa, destroying the ciliated epithelium and reducing the viscosity of mucosal secretions. This facilitates the spread of virus-laden exudate to the lower respiratory tract, with resultant necrosis and desquamation of the bronchi and alveoli. The disease is generally self-limiting, with acute symptoms lasting 2 to 7 days and lingering symptoms lasting another week.


The onset of influenza types A and B is sudden, marked by chills, fever, generalized aches and pains, headache, and photophobia. Respiratory symptoms begin with a scratchy, sore throat; substernal burning; and nonproductive cough. Later cough becomes severe and productive, and weakness, fatigue, and sweating persist. Influenza C produces milder symptoms.

Potential Complications

The most common complication is viral pneumonia or a secondary bacterial pneumonia. Individuals who have a compromised respiratory system and the elderly are most susceptible.

Diagnostic Tests

Tissue culture of nasal secretions or fluorescent antibody staining of secretions is positive for virus.



Analgesics for headache, aches, pains; nasal sprays for congestion (no aspirin for children because Reye’s syndrome may result); antitussives for cough; flu vaccine for prevention; amantadine for prevention of or early intervention for influenza type A in high-risk groups.

Adequate hydration; rest; careful handling of items in the environment and good handwashing to reduce the spread of the virus.