Asymptomatic Traveler With Tamiflu Resistant Pandemic H1N1

Recombinomics Commentary 20:20
July 4, 2009

Asymptomatic

Returned from San Francisco with mother and daughter (confirmed patient) on June 11

Admitted to United Christian Hospital (UCH) on June 12

Imported

Singapore Airlines (flight no SQ1) Arrived on June 11

Daughter (confirmed patient), mother, two sisters , a brother

The above data, from a Hong Kong DOH report describing pandemic H1N1 confirmed cases, is the only entry that matches reports on the 16 year old who was intercepted at the airport on June 11 and was subsequently found to be infected with Tamiflu resistant H1N1. The patient's flight had originated in San Francisco, and Singapore Airlines flight SQ1 is a nonstop flight from San Francisco to Hong Kong, providing additional evidence for Tamiflu resistant H1N1 in northern California.

The above description indicates the confirmed patient was the daughter in the traveling family described above, The cases is also described as asymptomatic, in contrast to media reports which indicated where was identified because of a fever. The cause of the discrepancy remains unclear, although the above report lists the age of the female patient as 36 instead of 16 and admission into United Christian Hospital instead of Queen Mary Hospital although transfer from one hospital to another could explain that discrepancy.

In any event, the above description is the only patient listed who flew into Hong Kong from San Francisco on June 11, and likely represents the case who had mild symptoms or was asymptomatic on arrival. Since the patient was not taking Tamiflu, the resistance would represent a fit pandemic H1N1 which is likely circulating in the United States.

Currently, efforts in the United States are directed toward severe cases and would likely miss either mild or asymptomatic individuals, allowing for silent spread of Tamiflu resistant pandemic H1N1.

The other two reported cases with H274Y (Demark and Japan) were from patients who were on a prophylactic dose. Although agencies have focused on a spontaneous mutation selected by the Tamiflu treatment, the reports do not exclude a mixture, with the H274Y on a minor population. A mixture would also raise concerns of silent spread of H274Y. The presence of h274Y in a treated patient may also be present in India, where a patient is asymptomatic, but shedding pandemic H1n1 in spite of a full course of Tamiflu treatment. The emergence of H274Y in treatment patients may simply reflect selection of this minor population. However, the presence of h274y in a minor population could lead to a jump onto another variant of pandemic H1H1, as was seen in seasonal H1N1. The fixing of H274Y in seasonal flu was preceded by H274Y in a number of clades and sub-clades, signaling multiple dependent introductions into hosts not taking Tamiflu.

The fixing of H274Y in seasonal flu has led to predictions that pandemic H1N1 with H274Y would emerge due to recombination between seasonal and pandemic H1N1. Others expected such dual infections to lead to acquisition of H274Y by reassortment, but none of the examples describe to date have involved reassortment and acquisition of human N1.

The reports of three examples of H274Y this week supports acquisition via recombination, and more such examples are expected in the near term, as more labs focus on H274Y in pandemic H1N1.