A third case of oseltamivir-resistant swine flu, announced today in Hong Kong, has flu experts worried that resistance to the drug is spreading. Unlike the previous two cases, the Hong Kong patient hadn’t taken oseltamivir herself, which suggests she picked up a resistant strain from someone else.
When Denmark reported its first known resistant case of 2009 A(H1N1) swine flu on Tuesday, scientists weren’t alarmed yet, because the virus most likely developed resistance while the patient was being treated and there was no evidence that she had infected anybody else. A second case, reported yesterday from Japan, also appears to have arisen while the patient took the drug. In the past, such drug-induced mutant viruses have often not spread very well.
The Hong Kong case is different: The patient, a 16-year-old girl intercepted at Hong Kong International Airport on 11 June after flying in from San Francisco, had only mild symptoms and never took oseltamivir, Hong Kong health authorities reported today. That suggests this strain is already circulating in California and may not be hampered by the resistance mutation.
“It’s very disturbing that, fresh into the human population, this [virus] appears now to be able to retain fitness despite having the mutation and to be able to spread,” virologist Jennifer McKimm-Breschkin of the Commonwealth Science and Industrial Research Organisation in Melbourne, Australia, told Bloomberg today.
Tests showed that the resistant virus is still susceptible to zanamivir, a chemical cousin of oseltamivir that some countries have added to their pandemic stockpiles.