Survival Rates After the Initiation of Antiretroviral Therapy Stratified by CD4 Cell Counts in Two Cohorts in Canada and the United States

Important note: Information in this article was accurate in 2002. The state of the art may have changed since the publication date.

Survival Rates After the Initiation of Antiretroviral Therapy Stratified by CD4 Cell Counts in Two Cohorts in Canada and the United States

AIDS (08.16.02) Vol.16; No. 12: P. 1693-1695 - Friday, September 13, 2002
Kenny C.W. Chan; Benita Yip; Robert S. Hogg; Julio S.G. Montaner; Michael V. O'Shaughnessy

In order to characterize patterns of survival among individuals initiating HAART in Canada and the United States, the authors conducted a population-based analysis of antiretroviral therapy with HIV-infected individuals enrolled in the British Columbia Drug Treatment Program. They then compared the BC data with the recent report from the CDC Adult and Adolescent Spectrum of Disease Project in the United States. The CDC report is a medical record review surveillance project conducted in 11 US cities.

Eligible patients (n=1,219 in BC; n=5,110 in CDC) were treatment na ve and initiated antiretroviral therapy with double or triple combination in 1994 or later. Rates of progression from the initiation of therapy to death were stratified by CD4 cell counts. Hazard ratios using the Cox method were computed using those patients who began treatment at a CD4 cell count of 500 cells/mm3 or greater as a reference.

Both cohorts showed a statistically significantly greater risk of death for those individuals who initiated treatment with a CD4 cell count below 200/mm3. There was no significant difference in risk of death when treatment began at a CD4 cell count 200-500 and 500 cell/mm3, or greater, in both cohorts.

Comparison between the BC and CDC studies of survival was conducted through Kaplan-Meier estimates. The overall 2 year survival rate was 93.4 percent and 80.9 percent, respectively. A lower survival rate was apparent in the CDC cohort at low baseline CD4 cell counts. In the cell count strata of 0-49 and 50-99 cells/mm3, the lower 95 percent confidence interval limits of the BC survival rates were 73.8 and 84.4 percent, which were higher than the CDC point estimates of 64.8 and 78.1 percent.

According to the authors, the results are consistent with recently published data regarding uniformly low rates of disease progression and death among patients initiating therapy with CD4 cell counts of 200/mm3 or greater. However, the reported death rates for patients initiating therapy with lower counts appear to be consistently lower at any CD4 cell count threshold in the BC cohort than in the CDC cohort.

The discrepancy in life span between BC patients and CDC patients requires a different explanation than use of antiretroviral treatment. The authors suggested the difference may be due to baseline differences in population mix, as age and ethnicity have been associated with survival, despite similar levels of cell count. In the BC study, the authors identified a previous AIDS diagnosis, CD4 cell count at initiation and baseline plasma HIV-RNA levels as significantly associated with death. However, of note is the fact that in multivariate analysis, only the CD4 cell count remained significantly associated with death.

The authors called for further study since other baseline characteristics such as sex balance, dual versus triple regimen use, socioeconomic status, risk factors and co- morbidities are variables that may account for the differences. Also, they suggested, access to health care may play a significant role. "Whereas all patients in the BC cohort have free access to all licensed antiretroviral therapy, plus laboratory and medical monitoring as part of the Canadian medical system, this is not necessarily the case in the United States," the authors concluded.
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