[Imputation of the date of HIV seroconversion in cohorts of haemophiliacs]

[Imputing missing data in public health: general concepts and application to dichotomous variables]

The presence of missing data in collected variables is common in health surveys, but the subsequent imputation thereof at the time of analysis is not. Working with imputed data may have certain benefits regarding the precision of the estimators and the unbiased identification of associations between variables. The imputation process is probably still little understood by many non-statisticians, who view this process as highly complex and with an uncertain goal. To clarify these questions, this note aims to provide a straightforward, non-exhaustive overview of the imputation process to enable public health researchers ascertain its strengths. All this in the context of dichotomous variables which are commonplace in public health. To illustrate these concepts, an example in which missing data is handled by means of simple and multiple imputation is introduced.

[Effect of distinct sociodemographic variables on progression of HIV infection in a cohort of drug users]

OBJECTIVE

To analyze whether the effectiveness of combined antiretroviral therapy in delaying progression to AIDS and death is affected by social inequities in a cohort of HIV-positive injecting drug users (IDUs).

METHODS

A cohort of 3,122 HIV-positive IDUs identified in the AIDS Information and Prevention Centers of the autonomous region of Valencia was analyzed, with further follow-up in 1,876. Progression to AIDS and death after seroconversion were calculated by Kaplan-Meier estimation according to sociodemographic variables (age, sex, education, marital status, length of addiction). Cox regression models were also fitted.

RESULTS

No significant differences were observed according to the variables considered when analyzing time to AIDS development. Evaluation of survival time revealed that individuals with further follow-up showed an excess of mortality (HR = 1.35; 95%CI: 0.20-1.54). For individuals without follow-up, mortality risk was reduced in those with secondary school education (HR = 0.51; 95%CI: 0.35-0.74) and with university education (HR = 0.41; 95%CI: 0.18-0.93) compared with those with no education. When individuals with follow-up were analyzed, the differences lost significance for those with secondary school education (HR = 0.92; 95%CI: 0.72-1.19) and university education (HR = 0.62; 95%CI: 0.35-1.11).

CONCLUSIONS

The mortality excess found in IDUs with lower educational levels, especially among those not seeking healthcare in the initial period after being identified as HIV-positive, highlights the need for interventions aimed at facilitating access to health systems, especially among the socially disadvantaged.

Changes in the incidence of tuberculosis in a cohort of HIV-seroconverters before and after the introduction of HAART

OBJECTIVE

To analyse incidence and determinants of tuberculosis in HIV-seroconverters before and after the introduction of HAART.

METHODS

Data from a multicenter cohort study of 2238 HIV-seroconverters between the 1980s and 2004 were analysed and censored by December 2004. Calendar year at risk intervals were pre-1992, 1992-1996 and 1997-2004. Incident tuberculosis was calculated as cases per 1000 person-years (p-y). Survival analyses using Kaplan-Meier and multivariate Cox regression allowing for late-entry were used. Proportional hazards assumptions were checked with tests based on Schoenfeld residuals.

RESULTS

Overall, 173 (7.7%) patients developed tuberculosis over 23 698 p-y at a rate of 7.3 cases per 1000 p-y [95% confidence interval (CI), 6.3-8.5]. Incident tuberculosis was higher in intravenous drug-users (IDUs), 12.3 per 1000 p-y compared with persons infected sexually, 3.8 per 1000 p-y (P < 0.001), and persons with clotting disorders (PCD), 2.7 per 1000 p-y (P < 0.001). A decreasing tuberculosis incidence trend was observed from 1995 in all categories. Highest tuberculosis rates, 44 per 1000 p-y, were observed prior to 1997 in IDUs infected with HIV for 11 years. In multivariable analyses women were less likely to develop tuberculosis [relative hazard (RH), 0.62; 95% CI, 0.41-0.96; P < 0.05) and IDUs were more likely to develop tuberculosis (RH, 3.0; 95% CI, 1.72-5.26, P < 0.001). In the HAART era, the hazard of developing tuberculosis was 70% lower (RH, 0.31; 95% CI, 0.17-0.54; P < 0.001). Before 1997, the risk of tuberculosis increased with time since HIV seroconversion, whereas it remained nearly constant in the HAART era.

CONCLUSIONS

Since the mid-1990s important decreases in tuberculosis have been observed in HIV-seroconverters that probably reflect the impact of both HAART and tuberculosis control programmes.

Gender differences in progression to AIDS and death from HIV seroconversion in a cohort of injecting drug users from 1986 to 2001

BACKGROUND

Although the consensus is that gender does not influence HIV progression, its relevance may depend on the setting.

AIM

To study gender differences in HIV progression to AIDS and death from 1986 to 2001 in a cohort of injecting drug user (IDU) seroconverters in Spain.

METHODS

Risk of AIDS and death in persons infected for the same length of time were compared through Kaplan-Meier, allowing for late entry, and Cox regression adjusting for gender, age, and calendar period (before 1992, 1992-1995, 1996-1998, 1999-2001) fitted as time dependent covariates.

RESULTS

Of 929 IDU, 24.7% were women. Median seroconversion year was 1993.3 for men and women. 44% of women and 34% of men received antiretroviral therapy. Risk of AIDS was lower in women in univariate (hazard ratio (HR) 0.72; 95%CI:0.51 to 1.01) and multivariate analyses (HR 0.73 95%CI:0.52 to 1.03). A 46% reduction in risk of AIDS for period 1999-2001 compared with 1992-1995 was seen in both men and women (HR: 0.56 (95%CI:0.36 to 0.87). As for mortality, women's risk of death was lower univariately (HR 0.67 95%CI:0.45 to 0.99) although compared with 1992-95, men experienced a 34% reduction in mortality during 1999-2001 (HR 0.66 95%CI:0.40 to 1.01), which was not statistically significant in women.

CONCLUSIONS

HIV progression was lower in female IDU before and after 1997 and their uptake of antiretroviral therapy was higher than male IDU. The inability to detect a reduction in mortality for women during 1999-2001 is probably attributable to lack of power. Differences in severity of addiction, drug using patterns, and competing causes of death may explain these findings.