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"Flu" season: are you ready?

Article Excerpt
"Flu" season is just around the corner. When do the symptoms reflect something more than the "common cold" and what--if anything--can be done to help afflicted patients? How can we prevent the spread of influenza? Who should be vaccinated, and which vaccine should be administered? Which patients are candidates for antiviral prophylaxis?

MICROBIOLOGY

Influenza is caused by orthomyxoviruses, mainly influenza A and B viruses, which invade the respiratory tract. Hemagglutinin (HA) and neuraminidase (NA) are 2 surface glycoproteins of the influenza virus that aid in viral replication. HA allows the virus to attach to the respiratory epithelial cells and NA causes the viruses to be released and dispersed from the infected cell. (1) Point mutations that occur during viral replication lead to antigenic drift (minor antigenic variations within the same subtype) in either HA or NA.

Although antibodies to surface proteins, especially HA, develop, protection against a new variant is not guaranteed. Antigenic drift occurs continuously in both influenza A and B viruses. As a result, circulating influenza viruses are constantly changing: hence, the need to modify the vaccine developed each influenza season. Antigenic shift (a major antigenic variation leading to the emergence of a new HA or NA) has occurred rarely only in influenza A virus. Three distinct HA subtypes (H1, H2, and H3) and 2 NA subtypes (N1 and N2) have been recognized as the cause of global epidemics. (2)

EPIDEMIOLOGY

The 2003-2004 influenza season in the United States lasted from October to May and peaked from November through January. Influenza A predominated. (3) Although influenza is generally viewed as an illness potentially devastating to elderly persons, it can lead to significant morbidity and mortality in otherwise healthy infants and toddlers. In the first 1 to 2 years of life, children are hospitalized for influenza-related illness at rates similar to those of high-risk adults (4) and older high-risk children. (5) Family members of children with influenza experience high rates of medical visits and absenteeism from work and school. (6) Excessive amounts of antibiotics are prescribed during periods when influenza is active in the community. (4) More than 150 influenza-associated deaths in patients younger than 18 years were reported in last year's influenza season. (3)

Worldwide pandemics have occurred at irregular intervals. In the 20th century, pandemics attributable to different influenza A virus subtypes occurred in 1900, 1918, 1957, 1968, and 1977. (1) Because the timing of such pandemics is unpredictable, the medical community must be prepared for such an outbreak.

SIGNS AND SYMPTOMS

In children, influenza manifests primarily with a sudden onset of systemic and...

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