The Power of III
August 15, 2009
August 15, 2009
On June 1, the patient was enrolled in an influenza antiviral treatment study and he began a 10-day course of oseltamivir.
A novel influenza A (H1N1) virus isolate from a specimen collected on May 31 was identified as susceptible to oseltamivir by pyrosequencing at CDC, but viruses isolated from specimens collected on June 11 and July 14 had the H275Y mutation, indicating oseltamivir resistance.
Antiviral treatment with high-dose oseltamivir (150 mg orally, twice a day) and rimantadine (100 mg orally, twice a day) was administered during June 26--July 1.
On August 10, CDC received other previously collected virus isolates from this patient for testing, and pyrosequencing of a virus isolated from a specimen collected on July 14 had the H275Y mutation, confirming oseltamivir resistance.
The above comments are from today's MMWR dispatch describing two immune-suppressed patients, who represent the first two confirmed cases of oseltamivir resistance in H1N1 pandemic swine flu in the United States. Both patients were from King County in Washington State and initial isolates from both patients were sensitive. In one patient, virus with H274Y was first detected in a sample collected 10 days after the start of treatment, while in the other patient, resistance was detected in a sample collected 18 days after the start of treatment. Because these patients were symptomatic at the start of treatment, the date of detectable resistance is unknown, in contrast to earlier patients who were asymptomatic at the start of prophylactic treatment and became symptomatic 5-6 days later. In the patients treated prophylatically, the appearance of symptoms in the short time frame after the start of treatment suggests the resistant virus was present as a minor population, and the treatment led to detection.