Novel swine--origin influenza A: the 2009 H1N1 influenza virus.

During April-May 2009, a novel H1N1 influenza virus was determined to be the cause of influenza outbreaks in North America. By June 2009, widespread infections were recorded all over the world and an ongoing pandemic was declared. The clinical manifestations ranged from a self limited illness to fatal disease. Current clinical data suggest that the highest infection rates and complications occur in children and young adults. In contrast to seasonal influenza, the rates of hospitalization and death in adults 65 years or older were low. Risk factors for severe disease are similar to those of seasonal influenza and include diverse medical conditions. However, pregnant women and children with neurodevelopmental disorders or chronic pulmonary conditions are at highest risk of developing severe disease. Rapid antigen detection tests have variable and suboptimal sensitivity for diagnosis of novel H1N1 influenza. Diagnosis is confirmed by real-time reverse transcriptase polymerase chain reaction or by virus isolation in cell culture. Treatment is recommended with oral oseltamivir or inhaled zanamavir for patients who are at risk of complications as well as those who are worsening clinically or have evidence of lower respiratory tract infection. Treatment with intravenous peramivir can be used in special situations when oral or inhaled antiviral therapy is not tolerated or considered inadequate. Inactivated and live attenuated vaccines are available. Current vaccination recommendations and infection control measures are discussed.