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Early Reports of pH1N1-Associated Illnesses for Current Flu Season

CDC issues health alert (December 24)

From November through December 2013, the Centers for Disease Control and Prevention (CDC) has received a number of reports of severe respiratory illness among young and middle-aged adults, many of whom were infected with influenza A (H1N1) pdm09 (pH1N1) virus. Multiple pH1N1-associated hospitalizations, including many requiring admissions to intensive care units, and some fatalities have been reported.

The pH1N1 virus that emerged in 2009 caused more illness in children and young adults than in older adults, although severe illness was seen in all age groups. The CDC says that while it is not possible to predict which influenza viruses will predominate during the entire 2013–2014 flu season, pH1N1 has been the predominant circulating virus so far. If the pH1N1 virus continues to circulate widely during the 2013–2014 season, illness that disproportionately affects young and middle-aged adults may occur, according to the agency.

The spectrum of illness observed thus far in the 2013–2014 season has ranged from mild to severe and is consistent with that of other flu seasons. Although the CDC has not detected any significant changes in pH1N1 viruses that would suggest increased virulence or transmissibility, the agency is continuing to monitor for antigenic and genetic changes in circulating viruses, and is watching morbidity and mortality surveillance systems that might indicate increased severity from pH1N1 virus infection.

The CDC recommends annual influenza vaccination for everyone 6 months of age and older. While vaccination is the best tool for the prevention of influenza and its complications, treatment with antiviral drugs — oral oseltamivir (Tamiflu, Genentech) and inhaled zanamivir (Relenza, GlaxoSmithKline) — is an important second line of defense for those who become ill to reduce morbidity and mortality.

Source: CDC; December 24, 2013.

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