Patterns of severe influenza in California, September 29, 2013–January 18, 2014

This report from the CDC's MMWR contains a world of information. It is available as free full text.

Key points:

This, the worst flu season since the 2009 pandemic, represents a resurgence of novel pandemic 2009 H1N1 influenza (pH1N1).  All of the severe (ICU admission) and fatal cases that were subtyped proved to be pH1N1.

Rapid influenza tests had low sensitivity. 42% false negative rate with PCR as the standard.

Risk factors for severe disease included lack of vaccination, medical comorbidities and obesity.

The report includes recommendations for anti-viral therapy:

Approximately 54% of hospitalized patients with fatal illness did not receive antiviral treatment at hospital presentation. Neuraminidase inhibitors have an excellent safety profile and empiric treatment with a neuraminidase inhibitor should be initiated as soon as possible for any hospitalized patient with suspected influenza (8). For outpatients with high-risk conditions and persons with progressive disease who are not being admitted, antiviral treatment is also recommended (9).¶ Observational studies have also reported modest clinical benefits when antiviral treatment is started late in the course of illness, which indicates that even patients admitted late in the course of illness should receive antiviral treatment (10). Either oral oseltamivir or inhaled zanamivir are recommended for treatment of suspected or confirmed influenza (http://www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm). Inhaled zanamivir should not be used for patients who are severely ill with influenza or intubated. For severely ill patients with influenza who cannot receive oral oseltamivir or inhaled zanamivir, intravenous zanamivir, an investigational drug, can be considered.** Oseltamivir resistance is low among circulating influenza viruses in the United States.

HT to Hospital Medicine Virtual Journal Club.