Influenza, Seasonal

Droplet Precautions

Influenza (also called the grippe or the flu) is an acute, highly contagious infection of the respiratory tract caused by influenza viruses from the family Orthomyxoviridae. Influenza viruses, which are usually seen during the colder months, are classified into three groups: Type A, the most prevalent, strikes every year, with new serotypes causing epidemics every 3 years; type B strikes annually and causes epidemics every 4 to 6 years; and type C is endemic and causes only sporadic cases. Epidemics tend to peak within 2 to 3 weeks after initial cases are diagnosed and subside within a month.

Although influenza affects all age groups, its incidence is highest in school-age children. However, its effects are most severe in persons who are young, elderly, or suffering from chronic disease. In these groups, influenza may lead to death.

Causes

Transmission of influenza occurs through inhalation of respiratory droplets from an infected person or by indirect contact with an object, such as a drinking glass or other item, that has been contaminated with respiratory secretions. The influenza virus then invades the epithelium of the respiratory tract, causing inflammation and desquamation.

One of the remarkable features of the influenza virus is its capacity for antigenic variation into numerous distinct strains, allowing it to infect new populations that have little or no immunologic resistance. Antigenic variation is characterized as antigenic drift (minor changes that occur yearly or every few years) and antigenic shift (major changes that lead to pandemics).

Complications

Complications that may occur with seasonal influenza include pneumonia, myositis, exacerbation of chronic obstructive pulmonary disease, Reye syndrome, myocarditis (rare), pericarditis (rare), transverse myelitis (rare), and encephalitis (rare).

Assessment Findings

After an incubation period of 24 to 48 hours, flu symptoms begin to appear: sudden onset of chills, fever of 101° to 104° F (38.3° to 40° C), headache, malaise, myalgia (particularly in the back and limbs), a nonproductive cough and, occasionally, laryngitis, hoarseness, conjunctivitis, rhinitis, and rhinorrhea. These symptoms usually subside within 3 to 5 days, but cough and weakness may persist. Fever is usually higher in children than in adults. Also, cervical adenopathy and croup are likely to be associated with influenza in children. In some patients (especially elderly patients), lack of energy and easy fatigability may persist for several weeks. Fever that persists longer than 5 days signals the onset of complications.

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