High Attack Rate in Tamiflu Resistant Cluster in Vietnam Recombinomics Commentary 00:25 December 10, 2009
In July 2009, during a 42-hour journey, 10 students socialized together in the same train carriage. None of the students knew each other before the journey, none had contact with a person with suspected influenza in the week before the trip, none were symptomatic during the journey, and none were previously or currently receiving oseltamivir. Fever developed in four of the students within 12 hours after arrival and in two more students within 48 hours after arrival (Fig. 1 in the Supplementary Appendix, available with the full text of this letter at NEJM.org). An additional case was identified in a traveler in a different carriage (Patient G). Nasal swabs, throat swabs, or both from all seven persons were positive for 2009 H1N1 RNA when tested with reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assays, and viruses were successfully cultured from specimens obtained from three of the persons. The H275Y substitution was detected retrospectively in diagnostic specimens obtained from all seven subjects before any oseltamivir treatment
The above description of efficient transmission of H274Y in pandemic H1N1 is from today's New England Journal of Medicine, which confirms the presence of fit virus with H274Y. The attack rate was high. At least seven of ten students were infected, and all had H274Y. Although all recovered, one patient continued to shed virus for 9 days. This cluster was in Vietnam in July and highlights the ease of transmission of H274Y.
Recent clusters of human to human transmission have been described in hospital settings in North Carolina and Wales and in North Carolina, 3 of 4 patients died, raising additional concerns that the H274Y currently transmitting is not only fit, but also lethal.
The high penetration rate in Vietnam suggests H274Y is widespread in mild cases, but is largely undetected because of limited testing. However, media reports in August suggested H274Y was spreading in Vietnam and recent reports suggest 6% of cases in Vietnam may have H274Y.
In the US, the detection of H274Y has recently increased almost 10 fold, signaling a crossing of a tipping point.
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