January 9, 2009

No Statistically Significant Clinical Differences Seen with Oseltamivir-Resistant Influenza A (H1N1) in Norway in 2007-2008

Several media reports in the past week have commented on a possible increase in pneumonia and/or sinusitis in patients from Norway with the new oseltamivir (Tamiflu)-resistant influenza A (H1N1) virus. For example, today’s NY Times article (page A10/A17, January 9th) cites a well-known biochemist stating that “Preliminary data out of Norway…suggested that the new strain was more likely to cause pneumonia”. This study from Norway was published early online in the February issue of Emerging Infectious Diseases (EID) journal on the CDC website (Hauge SH et al. Osetamivir-Resistant influenza A (H1N1, Norway, 2007-08. Emerg Infect Dis. 2009 February). Of note, this study did not find a statistically significant increase in either pneumonia or sinusitis in persons infected with oseltamivir-resistant influenza A (H1N1).

Specifically, this study from Norway reported the following:

“Overall, the observed clinical manifestations associated with influenza viruses A (H1N1) in this study were as expected for seasonal influenza. No differences were noted for virus shedding, primary symptoms, or overall complication and hospitalization rates caused by oseltamivir-resistant and –susceptible viruses. We did find, although not a statistically significant finding, that patients infected with a resistant virus appeared to be more likely than those infected with a susceptible virus to have pneumonia or sinusitis…Because of our limited sample size, the precision of our estimates is low, but they do indicate findings that warrant further.”

Certainly, further study is warranted of these preliminary findings. At the same time, however, it should be emphasized that no statistically significant differences have been reported in the clinical manifestations of patients with oseltamivir-resistant and oseltamivir–susceptible influenza A (H1N1) infection.

Daniel R. Lucey, MD, MPH

EROne Institutes, Washington Hospital Center

Adjunct Professor of Microbiology and Immunology

Georgetown University Medical Center

Washington, D.C.

Website for this posting: www.BePast.org

DRL23@Georgetown.edu