Emerg Infect Dis. Oseltamivir-Resistant Influenza Viruses A (H1N1), Norway, 2007?08

[Giuseppe]

Oseltamivir-Resistant Influenza Viruses A (H1N1), Norway, 2007?08 (EID, abstract, edited)

[Original Full Document: LINK. EDITED.]

DOI: 10.3201/eid1502.081031

Suggested citation for this article: Hauge SH, Dudman S, Borgen K, Lackenby A, Hungnes O. Oseltamivir-resistant influenza viruses A (H1N1), Norway, 2007?08. Emerg Infect Dis. 2009 Feb; [Epub ahead of print]

Oseltamivir-Resistant Influenza Viruses A (H1N1), Norway, 2007?08

Siri H. Hauge, Susanne Dudman, Katrine Borgen, Angie Lackenby, and Olav Hungnes

Author affiliations: Norwegian Institute of Public Health, Oslo, Norway (S.H. Hauge, S. Dudman, K. Borgen, O. Hungnes); and Health Protection Agency, London, UK (A. Lackenby)


In Norway in January 2008, unprecedented levels of oseltamivir resistance were found in 12/16 influenza viruses A (H1N1) tested. To investigate the epidemiologic and clinical characteristics of these viruses, we used sequence analysis to test all available subtype H1N1 viruses from the 2007?08 season for resistance. Questionnaires from physicians provided information on predisposing diseases, oseltamivir use, symptoms, and complications. Clinical data were obtained for 265 patients. In total, 183 (67.3%) of 272 viruses were oseltamivir resistant. Resistance was not associated with prior use of antiviral drugs. Symptoms and hospitalization rates did not differ for patients infected with a resistant or a susceptible virus. Oseltamivir-resistant influenza viruses A (H1N1) did not show diminished capability to spread in the absence of selective pressure. The ability of these viruses to sustain their fitness and spread among persons should be considered when shaping future strategies for treating and preventing seasonal and pandemic influenza.

-
-----

 

[mixin]

Re: Emerg Infect Dis. Oseltamivir-Resistant Influenza Viruses A (H1N1), Norway, 2007–08

Re: Emerg Infect Dis. Oseltamivir-Resistant Influenza Viruses A (H1N1), Norway, 2007–08

Some additional snips:

No difference in virus shedding was observed between susceptible and resistant viruses

Median ages of those infected with a resistant and a susceptible virus were 31 and 21 years, respectively.

The highest proportion of resistant virus infection was found for those 25-59 years of age (102/138, 73.9%) and differed significantly from the proportion for only those 5-14 years of age (25/45, 55.6%)

We obtained viruses H1N1 from 18/19 counties .The oseltamivir resistance proportion was >80% in 8 counties in southern Norway, compared with 63.5% in the rest of the country

Of all 272 patients, 2 had been vaccinated against influenza and were both infected with a resistant virus.

Predisposing disease more than doubled the risk for complications but was not clearly associated with being infected with a resistant virus

Resistant virus infection was not associated with any particular symptom. Of 241 patients, 58 (24.1%) had >1 complications recorded, but no difference was observed between those infected with a resistant virus and those infected with a susceptible virus. Bronchitis and pneumonia were the most frequent complications, reported for 22 and 17 patients, respectively.

The attack rates of pneumonia and of sinusitis were higher for those infected with a resistant virus than for those infected with a susceptible virus, although the risk ratios were not statistically significant after adjusting for age, gender, and predisposing disease

The resistant and susceptible viruses were closely related and were not distinguishable in hemagglutination inhibition tests

Changes in recent influenza viruses A (H1N1) may have provided a genetic background that permits H274Y mutants to replicate and transmit. Previous studies have concluded that resistant viruses are less pathogenic and less transmissible than their susceptible counterparts. In contrast, however, reverse genetics-derived mutants (A/WSN/33 or PR8 backbone) had the same phenotype as wild type viruses in vitro and in vivo.

A recent study on the enzymatic properties of the N1 neuraminidase of the resistant viruses from the 2007-08 season suggested some genetic background changes that could potentially be involved.

Symptoms and hospitalization rates did not differ for patients infected with a resistant or a susceptible virus.

Oseltamivir-resistant influenza viruses A (H1N1) did not show diminished capability to spread in the absence of selective pressure.

The ability of these viruses to sustain their fitness and spread among persons should be considered when shaping future strategies for treating and preventing seasonal and pandemic influenza.