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Secondary bacterial infections have been found in approximately 30 percent of fatal cases of 2009-H1N1 influenza A. Bacteria frequently reported include Streptococcus pneumoniae and Staphylococcus aureus, including methicillin-resistant strains in some cases. These infections can be prevented with antimicrobial (i.e., antibacterial, antiviral, antifungal agents) therapy during early treatment of 2009-H1N1 influenza A.a

Risk of severe or fatal illness is highest in three groups: pregnant women, especially during the third trimester of pregnancy; children younger than 2 years of age; and people with chronic lung disease, including asthma. However, significant numbers of severe cases occurred in previously healthy young people in the absence of any known predisposing risk factors. In addition, the overall fatality rate was highest in persons over 50 years of age (Louie et al., 2009a).

Comorbidities associated with severe 2009-H1N1 influenza A include cardiopulmonary diseases, diabetes, pregnancy, and morbid obesity.

Antiviral treatment and resistance: The 2009-H1N1 influenza A virus is sensitive to the neuraminidase inhibitors oseltamivir (Tamiflu®) and zanamivir (Relenza®) and resistant to amantadine and rimantadine. There have, however, also been recent sporadic reports of oseltamivir resistance. Accumulating evidence suggests that prompt treatment of confirmed or suspected 2009-H1N1 influenza A with antiviral drugs reduces the severity of illness and improves the chances of survival.

SOURCES: CDC (2009b); Fukuda (2009); Munayco et al. (2009); Pourbohloul et al. (2009); WHO (2009f).

Workshop presentations offered epidemiological and clinical perspectives on the developing pandemic that ranged from the global to the local. The following discussion highlights information that contrasted with general trends as described in Box WO-3, or which provided novel clinical insights on the 2009-H1N1 influenza A virus.

The United States and Mexico

As is typical for the Northern Hemisphere, overall influenza activity declined over the summer in the United States. Localized outbreaks of 2009-H1N1 influenza A, some of them intense, however, continued to occur in different parts of the country (PCAST, 2009). More than 80 outbreaks occurred in summer camps in more than 40 states (Stein, 2009), and the southern United States, where many

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