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Resistant influenza activity increased in the Southern Hemisphere

Oseltamivir resistance recently detected on three continents.

Issue: October 2008

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Increased incidence of oseltamivir-resistant influenza was reported in several countries in the Southern Hemisphere from July 6 to Aug. 9, 2008, according to findings reported by WHO.

Influenza A(H3) and B virus circulation has been widespread in New Zealand. Argentina has reported sporadic outbreaks of influenza A(H1), and Brazil has reported sporadic incidences of influenza A and B.

Incidences of influenza A and B have been reported in Chile, where testing revealed that four of 32 reported cases of influenza A(H1N1) virus showed the specific neuraminidase mutation (H274Y) associated with oseltamivir (Tamiflu, Roche) resistance, according to the findings. In Australia, all ten influenza A(H1N1) viruses that were reported showed a similar mutation.

The National Institute of Communicable Diseases in South Africa conducted genotypic analysis on 107 influenza A(H1N1) isolates for oseltamivir resistance. All of them were resistant, according to the findings reported to WHO. No unusual clinical features or underlying conditions were found, and only one of the 107 patients was being treated with oseltamivir, according to the findings. The country has isolated 139 influenza A(H1N1) viruses to date in 2008.

Other countries south of the equator that reported oseltamivir-resistant strains in recent months include Madagascar and Seychelles. – by Rob Volansky

This report from WHO provides an update on surveillance of oseltamivir (Tamiflu, Roche) resistance in influenza viruses in the Southern Hemisphere. It demonstrates an increase in the frequency of resistance in influenza A(H1N1) viruses. Results of testing of South African isolates by the National Institute of Communicable Diseases in Johannesburg are particularly striking in the absence of recent patient exposure to the drug. Data from neighboring countries would be of interest, but they lack National Influenza Centers.

The report is timely in anticipation of the upcoming influenza season in the Northern Hemisphere, provides a reminder of the importance of monitoring the frequency of drug resistance in influenza and provides an additional reason for receipt of influenza vaccine this year.

The results also demonstrate the value of regional and global infectious disease surveillance systems. They highlight the importance of providing adequate support for national public health institutions to develop the capacity to perform this important work in an accurate and timely manner to ensure availability of the information to clinicians and public health officials.

– James M. Hughes, MD

Infectious Disease News Editorial Board member

For more information:

• Influenza A(H1N1) virus resistance to oseltamivir - 2008 influenza season, southern hemisphere. WHO website.
  www.who.int/csr/disease/influenza/H1N1webupdate20082008_kf.pdf.