HIV-1 Strain and Primary Drug Resistance in Canada
Surveillance Report to June 30, 2002

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Results at a Glance

This report is organized into five sections. The first section provides an overview of Health Canada's Canadian HIV Strain and Drug Resistance Surveillance Program (CHSDRSP). The second section describes the methodologies used for data collection, transfer and analyses. The third section describes the primary drug resistance results from the program. This section also summarizes results from other key studies conducted in Canada, the United States, and Western Europe. The fourth section describes HIV-1 subtype results from the program. The fifth section describes the sentinel surveillance arm of the CHSDRSP, which serves the provincial public health laboratories by testing samples from individuals with unusual clinical manifestations and/or with unusual laboratory results for HIV subtype and drug resistance (if requested).

This part of the report provides a summary of the main findings:

• The overall prevalence of primary drug resistance to at least one antiretroviral drug is 7.1% in the sample population of 847 individuals with newly diagnosed HIV infection who have never received treatment.
  
  
• Multi-drug resistance (protease inhibitors/nucleoside reverse transcriptase inhibitors and non-nucleoside reverse transcriptase inhibitors/nucleoside reverse transcriptase inhibitors) has been identified in six treatment naVve individuals (0.7%) with newly diagnosed HIV in the sample population.
  
  
• Resistance to nucleoside reverse transcriptase inhibitors has been observed in cases with newly diagnosed HIV infection in this sample population as early as 1998; resistance to non-nucleoside reverse transcriptase inhibitors and protease inhibitors as well as multi-drug resistance have also been observed in such cases.
  
  
• Primary drug resistance has been observed in females and males; across different age groups, ethnicities, and exposure categories; in HIV-1 subtype A, B, and C infections; and in recent and prevalent HIV infections.
  
  
• In Canada, HIV-1 subtype B continues to predominate, 93.1% of the samples subtyped belonging to this group, but subtypes A, C, D, E (also known as the circulating recombinant A/E), recombinant A/B, recombinant A/C, and recombinant A/G have been identified across Canada
  
  
• There is geographic variation with respect to the prevalence of non-B HIV-1 subtypes. This variation is likely related to travel and migration from countries where other subtypes predominate.
  
  
• Significantly higher proportions of non-B infections were detected among females (compared with males), among people reporting heterosexual contact as their primary exposure factor, and among people of Black, Asian or mixed ethnicities.

Public Health Implications

• The prevalence of primary drug resistance can be used to develop population-based recommendations for initial therapies (especially for pregnant women and for use in post-exposure prophylaxis).
  
  
• The extent to which drug-resistant strains of HIV are being transmitted can serve as an indicator to evaluate the effectiveness of prevention programs.
  
  
• HIV isolates from different populations and changes over time can be monitored to evaluate diagnostic and screening algorithms to ensure that all circulating strains are adequately detected.
  
  
• HIV subtype data can be used for the research and development of vaccines.
  
  
• Increased knowledge about HIV genetic diversity will be useful in monitoring the spread of HIV in Canada including assessing transmission patterns and disease progression.

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