Excerpts from the Canada Communicable Disease Report, issued today, regarding drug resistance:
J.
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http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/08vol34/dr-rm3403a-eng.php
Canada Communicable Disease Report
1 March 2008 Volume 34 Number 03
[Table of Contents]
Influenza in Canada: 2006-2007 Season
F Reyes, MHSc (1), S Aziz, MSc (1), Y Li, PhD (2), JF Macey, MSc (1), B Winchester, MSc (1), M Garner, MSc (1), P Huston, MD, MPH (1), A King, MD, MHSc, FRCPC (1)
1. Centre for Immunization and Respiratory Infectious Diseases, Public Health Agency of Canada, Ottawa, Ontario
2. Influenza and Respiratory Viruses Section, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba
Drug susceptibility tests
Amantadine Resistance
A rapid assay has been established at the NML to test influenza A viruses for resistance to amantadine. Polymerase chain reaction (PCR) and sequence analysis were used to detect drug resistance markers among 1,027 influenza A viruses (including 273 A (H1N1) and 754 A (H3N2) viruses) during the 2006-2007 season. Of the total 1,027 influenza A isolates tested, 27.4% were resistant to amantadine, including 1.1% (3/273) resistance among the A (H1N1) and 36.9% (278/754) among the A (H3N2) viruses. The remaining 76.2% (270/273) A (H1N1) and (476/754) A (H3N2) viruses were sensitive to amantadine (Table 4).
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Oseltamivir Resistance
The influenza virus neuraminidase (NA) inhibitors have recently been licensed for the prophylaxis and treatment of influenza virus infection in humans. In order to monitor the potential development of resistance, a new chemiluminescent (CL) neuraminidase assay was established at NML to test influenza field isolates for susceptibility to oseltamivir (Tamiflu?). A total of 1,048 influenza isolates were screened for oseltamivir resistance, (including 275 A (H1N1), 648 A (H3N2) and 125 influenza B viruses), of which only one A (H3N2) virus was resistant to oseltamivir (0.15% of A (H3N2) viruses tested and 0.10% of all influenza viruses tested).
Discussion
During the 2006-2007 influenza season, a lower level of resistance compared to the 2005-2006 season to the antiviral amantadine was detected among the circulating influenza A (H3N2) viruses, however the level of resistance observed was not as high as what was observed in the 2005-2006 season (91.5% or 463/506). On the basis of amantadine resistance patterns observed to date, PHAC continues to recommend against the use of amantadine for the treatment and prevention of influenza(10). During the 2006-2007 influenza season, the NML also monitored antiviral resistance to neuraminidase inhibitors among circulating influenza viruses. Only one A (H3N2) virus was found to be resistant to oseltamivir among the 1,048 influenza A and B viruses tested. The resistant isolate came from an immunocompromised individual who was treated with both oseltamivir and amantadine for influenza and pneumonia. An early isolate sent for antiviral sensitivity testing, showed resistance to amantadine but was sensitive to oseltamivir. As the patient's condition did not improve, repeat testing on a second isolate showed resistance to both amantadine and oseltamivir indicating that the development of oseltamivir resistance was treatment-associated. The development of antiviral resistance is not unexpected, particularly in immunocompromised individuals who may receive protracted and repeated treatment courses. These findings underscore the importance of influenza antiviral sensitivity testing to monitor for resistance in Canada and to inform appropriate use of antiviral medications to reduce the impact of influenza and to contribute to the global understanding of antiviral resistance patterns.
J.
__________
http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/08vol34/dr-rm3403a-eng.php
Canada Communicable Disease Report
1 March 2008 Volume 34 Number 03
[Table of Contents]
Influenza in Canada: 2006-2007 Season
F Reyes, MHSc (1), S Aziz, MSc (1), Y Li, PhD (2), JF Macey, MSc (1), B Winchester, MSc (1), M Garner, MSc (1), P Huston, MD, MPH (1), A King, MD, MHSc, FRCPC (1)
1. Centre for Immunization and Respiratory Infectious Diseases, Public Health Agency of Canada, Ottawa, Ontario
2. Influenza and Respiratory Viruses Section, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba
Drug susceptibility tests
Amantadine Resistance
A rapid assay has been established at the NML to test influenza A viruses for resistance to amantadine. Polymerase chain reaction (PCR) and sequence analysis were used to detect drug resistance markers among 1,027 influenza A viruses (including 273 A (H1N1) and 754 A (H3N2) viruses) during the 2006-2007 season. Of the total 1,027 influenza A isolates tested, 27.4% were resistant to amantadine, including 1.1% (3/273) resistance among the A (H1N1) and 36.9% (278/754) among the A (H3N2) viruses. The remaining 76.2% (270/273) A (H1N1) and (476/754) A (H3N2) viruses were sensitive to amantadine (Table 4).
________
Oseltamivir Resistance
The influenza virus neuraminidase (NA) inhibitors have recently been licensed for the prophylaxis and treatment of influenza virus infection in humans. In order to monitor the potential development of resistance, a new chemiluminescent (CL) neuraminidase assay was established at NML to test influenza field isolates for susceptibility to oseltamivir (Tamiflu?). A total of 1,048 influenza isolates were screened for oseltamivir resistance, (including 275 A (H1N1), 648 A (H3N2) and 125 influenza B viruses), of which only one A (H3N2) virus was resistant to oseltamivir (0.15% of A (H3N2) viruses tested and 0.10% of all influenza viruses tested).
Discussion
During the 2006-2007 influenza season, a lower level of resistance compared to the 2005-2006 season to the antiviral amantadine was detected among the circulating influenza A (H3N2) viruses, however the level of resistance observed was not as high as what was observed in the 2005-2006 season (91.5% or 463/506). On the basis of amantadine resistance patterns observed to date, PHAC continues to recommend against the use of amantadine for the treatment and prevention of influenza(10). During the 2006-2007 influenza season, the NML also monitored antiviral resistance to neuraminidase inhibitors among circulating influenza viruses. Only one A (H3N2) virus was found to be resistant to oseltamivir among the 1,048 influenza A and B viruses tested. The resistant isolate came from an immunocompromised individual who was treated with both oseltamivir and amantadine for influenza and pneumonia. An early isolate sent for antiviral sensitivity testing, showed resistance to amantadine but was sensitive to oseltamivir. As the patient's condition did not improve, repeat testing on a second isolate showed resistance to both amantadine and oseltamivir indicating that the development of oseltamivir resistance was treatment-associated. The development of antiviral resistance is not unexpected, particularly in immunocompromised individuals who may receive protracted and repeated treatment courses. These findings underscore the importance of influenza antiviral sensitivity testing to monitor for resistance in Canada and to inform appropriate use of antiviral medications to reduce the impact of influenza and to contribute to the global understanding of antiviral resistance patterns.
