US Spike in H1N1Tamiflu Resistance Signals Fixing Start Recombinomics Commentary 23:55 December 18, 2009
A total of 44 cases of oseltamivir resistant 2009 influenza A (H1N1) viruses have been identified in the United States since April 2009, including 15 newly identified cases since last week.
Of the 44 total cases identified, 27 patients had documented exposure to oseltamivir through either treatment or chemoprophylaxis, 15 patients are under investigation to determine exposure to oseltamivir, and two patients had no documented oseltamivir exposure. Occasional development of oseltamivir resistance during treatment or prophylaxis is not unexpected.
The above comments are from today's (week 49) CDC weekly update. The jump of 15 cases is more than double than the 7 reported in week 45, which was more than double any prior week. The 15 equals the combined total for the past four weeks and doubles the total for the past five weeks. The recent numbers signal the crossing of a tipping point and highlight the more efficient transmission and detection of H274Y in pandemic H1N1.
This change was also supported by H1N1 sequences released by NIID in Japan. 68 full sequences were deposited at GISAID, and 8 had H274Y. These eight were among the most recent collections, further signaling a recent change.
The H274Y positive sequences from Japan included an isolate that had D225E plus additional markers which matched two H274Y isolates form the US, suggesting that other isolates in this sub-clade also had H274Y circulating as an undetected sub-population. These same markers were in three isolates from Texas. Recently deposited sequences by the US CDC and NIID in Japan, demonstrated that the sub-clade was large and widespread in both countries. Thus, the dramatic jumps in cases will continue if recent cases are tested for H274Y.
Flu levels are declining in the US and Japan. However, the decrease in cases allows for the rapid emergence of virus with novel polymorphisms. The level of seasonal flu is close to zero in both countries, suggesting that the next wave will draw from swine H1N1, and the emerging strain will likely have high levels of H274Y, leading to a fixing of H274Y in pandemic H1N1, as happened in seasonal H1N1.
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