"Patients with NB are more likely to have a bacterial co-infection. Patients with heart disease and cancer are more likely to have a hemorrhagic condition in their lungs. It is important to bear in mind that patients with underlying medical conditions must be adequately monitored, since they are at greater risk of developing a severe H1N1 infection," said Dr. Mauad. In these patients, H1N1 infection may present as a potential fatal disease, requiring early and prompt intensive care management, including protective ventilation strategies and adequate hemodynamic management. "We found that 38 percent of these patients had a bacterial infection (bronchopneumonia). This has important consequences because these patients need to receive antibiotic therapy, in addition to antiviral therapy."

The researchers also found evidence of an influenza-associated "cytokine storm," an aberrant immune response in the lungs of certain individuals, which was almost certainly involved in the pathogenesis in these fatal cases of the H1N1 infection. "[This] suggests that an overly vigorous host inflammatory response triggered by the viral infection may spill over to and damage lung tissue, thereby causing acute lung injury and fatal respiratory failure," noted John Heffner, M.D., past president of the ATS.

Further research is needed to understand precisely how and why certain patients succumb to a fatal progression when infected with H1N1. While most patients experience a mild illness with no lasting effects, this research lays important groundwork for future efforts by defining the histological patterns associated with a fatal infection.

"We would like to deepen our efforts into the understanding of the immune responses in cases of severe infection," said Dr. Mauad. "This could ultimately lead to new therapeutic approaches."

Source: American Thoracic Society