HIV-1 Strain and Primary Drug Resistance in Canada

Surveillance Report to June 30, 2001

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Technical Notes

Data Collection and Reporting

It is important to note that the results presented here represent individuals who sought testing, were properly diagnosed, and were reported as HIV positive. Furthermore, they represent those individuals for whom sufficient serum specimen, taken for the purposes of diagnostic testing, was available to send to the National HIV Laboratories and, of these, the subset for whom subtype analysis and/or primary drug resistance genotyping was completed as of June 30, 2000. The quality of samples received by the National HIV Laboratories also determines whether subtype and primary drug resistance results can be generated. Typically, the laboratories make at least two attempts on samples that are difficult to amplify with the in-house and consensus Group M primers. The National Laboratory for HIV Genetics is currently in the process of examining the use of other primer sets for RT-PCR amplification.

The epidemiologic data collected through the CHSDRSP contain information included in the National HIV/AIDS reporting form plus additional data that allow interpretation of the laboratory results. These additional data include type of laboratory specimen sent, date of last negative HIV test, history of seroconversion (if any), anti-retroviral treatment history (if any), and viral load count at diagnosis.

The quality and completeness of epidemiologic data remain problematic (see Data Limitations section) and one of the key roles of federal Field Surveillance Officers is to work with the provincial and territorial health partners to facilitate the collection and timely reporting of these data to Health Canada.

Exposure Category Hierarchy

HIV cases were assigned to a single exposure category according to an agreed-upon hierarchy of risk factors. This hierarchy is described in more detail in the HIV and AIDS in Canada Surveillance Report available by contacting the Division of HIV/AIDS Epidemiology and Surveillance or electronically at www.hc-sc.gc.ca/hpb/lcdc/publicat.html

(select LCDC Periodicals & Serials, and then select HIV and AIDS in Canada).

Analysis of Drug Resistance

Although both genotypic and phenotypic testing methods are well established, each has its limitations. Both kinds of test provide information only on the virus that predominated at the time of sampling and are unable to identify virus that may be present as a result of past drug exposures. This is particularly important, as "minority" species of virus may become predominant under selective drug pressures that do not completely inhibit viral replication. Both assays are technically difficult to perform when the concentration of virus is < 1,000 copies/mL and may require highly specialized laboratory facilities and personnel. The ability of both assays to quantify resistance to certain drugs has not yet been determined. Phenotypic testing is expensive, at a cost of about US$800 per test. In genotypic testing, repeat analyses may be required since mutations strongly associated with drug resistance continue to be "discovered" and their complex interactions are only now beginning to be understood.

Interpretation of Drug Resistance

The interpretation of genotypic and phenotypic test results for patient care is still uncertain and under active research. The complexity of this task is compounded by the following factors: genotypic and phenotypic test results may not correlate with one another, clinical relevance varies from drug to drug, the concentrations at which a drug is ineffective has not been determined in vivo, and the extent to which pharmaceutical interactions influence resistance is not well known. Appendix 2 lists the mutations that were included as primary drug resistance mutations in the results presented in this report. It is anticipated that this list will change as new information on drug resistance mutations becomes available over time. International expert review panels have been formed. These meet periodically to review the latest laboratory and clinical findings in the development of guidelines to interpret genotypic and phenotypic drug resistance mutations for clinical management. A similar panel of experts is being assembled to identify and standardize mutations useful for primary drug resistance surveillance.

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