Vietnamese health officials have reported a cluster of drug-resistant H1N1 cases.

In a paper published in the New England Journal of Medicine they report that 10 students travelled together on a 42-hour train journey in July this year and at least six of them later developed tamiflu-resistant swine flu. The paper notes that the students did not know each other before the train ride and had no contact with people suspected of H1N1 infection. Nor had any of them received tamiflu (oseltamivir).

“In this cluster, infection developed in at least 6 of the 10 people who were probably exposed to the index patient; this shows that resistant 2009 H1N1 viruses are transmissible and can replicate and cause illness in healthy people in the absence of selective drug pressure,” write the Vietnam H1N1 Investigation Team. “… The loss of oseltamivir as a treatment option for severe 2009 H1N1 infection could have profound consequences.”

Earlier this month the World Health Organization reported two clusters of patients infected with tamiflu-resistant H1N1, one in Wales and one in North Carolina. However both these incidents involved patients whose immune systems were already weakened and the virus was probably passed between patients in each group.

“This [the Vietnam outbreak] is different and it does raise the levels of concern. But it also I think reinforces the message that we do need to be constantly monitoring for this. And reporting it as quickly as it’s observed,” Charles Penn of the WHO told the Canadian Press.

All the patients in the Vietnamese case eventually recovered.

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