PANDEMIC INFLUENZA A (H1N1) 2009: PATHOGENESIS AND CLINICAL FEATURES

Abstract

Pandemic 2009 H1N1 virus is able to bind to alpha 2,6-linked receptors found on the surface of cells located deep in the lungs that seasonal influenza virus cannot bind, suggesting why people with the pandemic H1N1 influenza can experience more severe viral pneumonitis as compared to seasonal influenza. Although the initial viral load was found to be similar to that of patients with mild disease, there was a slower decline in viral load for severe cases of 2009 H1N1 virus infection. The main pathological features in the lung are varying degrees of diffuse alveolar damage with hyaline membranes and septal edema, tracheitis, and necrotizing bronchiolitis. Analyses have suggested that clinical manifestations of 2009 H1N1 influenza and seasonal influenza are similar with fever, nonproductive cough, sore throat, myalgia, malaise, chills, rhinorrhea, headache and dyspnea. Gastrointestinal symptoms occur more commonly than in seasonal influenza. Patients requiring hospitalization for 2009 H1N1 virus infection are much more likely to have underlying medical conditions. Pregnant women, especially in their second and third trimester, are also at a higher risk for severe disease. A number of infected patients with diffuse viral pneumonitis associated with severe hypoxemia become critically ill and require intensive care admission. Many hospitalized patients have had lymphocytopenia and elevations in levels of serum aminotransferases, lactate dehydrogenase, creatine kinase, and creatinine.