Correlation of pandemic (H1N1) 2009 viral load with disease severity and prolonged viral shedding in children.

The influenza A pandemic (H1N1) 2009 virus, initially identified in Mexico and the United States in April 2009, has been reported in >213 countries (1). Severe illness and death can occur in humans infected with this virus, particularly young persons and pregnant women (2–5). Recent data from the United States showed that almost half of hospitalized case-patients were children <18 years of age and suggested that antiviral drugs were beneficial in these patients, especially when initiated early (6). This finding implies that the successful control of viral replication by using antiviral drugs is associated with a good clinical outcome. Because viral replication is necessary for disease pathogenesis in other influenza infections (7,8), information on the correlation between viral load and the clinical spectrum of illnesses among persons infected with pandemic (H1N1) 2009 virus is emerging. However, viral replication patterns and the effect of antiviral drugs on viral load have not been adequately studied. We undertook the present study to characterize the kinetic changes in viral load and shedding in a hospital-based cohort by real-time reverse transcription–PCR (RT-PCR) and to analyze the factors that influence the rate of viral RNA clearance. A correlation between the virologic profile and the clinical features of pandemic (H1N1) 2009 virus–infected patients would provide essential information for epidemiologic control and clinical management in terms of antiviral therapy and infection control approaches.