tamiflu resistance update, page-9

Texas Tamiflu Resistance Cluster Confirmed
Recombinomics Commentary 21:19
August 31, 2009


Influenza A/H1N1 (novel) 5 2 (40%) 0 (0) 5 5 (100%)

The above description is from the week 32 MMWR surveillance report from the Texas Department of State Health Services. The number of H1N1 isolates tested for oseltamivir resistance rose for 3 to 5, and both new isolates were resistant (presumably H274Y). It is likely that these two cases are those on the Mexican border which were disclosed and denied earlier this month.


Although both cases were on the Mexican border (see map), they were at opposite ends of the Texas border, raising concerns that resistance in Texas was widespread. Indeed, as noted above, the rate to date in Texas is 40% (2/5). Initial reports speculated that the resistance was linked to cross-border access to Tamiflu in Mexico. However, the US border with Mexico extends well beyond Texas, so cross border traffic is not limited to Texas, or the two locations described.

The clustering of these cases in Texas, but at widely separated locations is similar to the furst two pandemic H1N1 cases in southern California. Both were reported at the same time, but were not linked, raising concern that the H1N1 Tamiflu resistance was widespread.


Two cases in Texas in the same report raise similar concerns. Texas has only tested five pandemic H1N1 samples, so the two positives clearly dictate more aggressive testing is warranted.


There has been a recent resurgence of cases in Mexico, and these two resistant cases raise concerns that the resurgence is linked to resistance, which may be circulating as a minor species or may be evolutionarily fit, as suggested for the two isolates from northern California.

Release of the sequences from the Texas isolates would be useful, as would more testing of cases pre and post oseltamivir treatment.