Using HIV Sequence and Epidemiologic Data to Assess the Effect of Self-referral Testing for Acute HIV Infection on Incident Diagnoses in San Diego, California

Abstract

Background: Because recently infected individuals disproportionately contribute to the spread of human immunodeficiency virus (HIV), we evaluated the impact of a primary HIV screening program (the Early Test) implemented in San Diego.

Methods: The Early Test program used combined nucleic acid and serology testing to screen for primary infection targeting local high-risk individuals. Epidemiologic, HIV sequence, and geographic data were obtained from the San Diego County Department of Public Health and the Early Test program. Poisson regression analysis was performed to determine whether the Early Test program was temporally and geographically associated with changes in incident HIV diagnoses. Transmission chains were inferred by phylogenetic analysis of sequence data.

Results: Over time, a decrease in incident HIV diagnoses was observed proportional to the number primary HIV infections diagnosed in each San Diego region (P < .001). Molecular network analyses also showed that transmission chains were more likely to terminate in regions where the program was marketed (P = .002). Although, individuals in these zip codes had infection diagnosed earlier (P = .08), they were not treated earlier (P = .83).

Conclusions: These findings suggests that early HIV diagnoses by this primary infection screening program probably contributed to the observed decrease in new HIV diagnoses in San Diego, and they support the expansion and evaluation of similar programs.

Keywords: HIV diagnostic tests; incidence; models/projections; molecular epidemiology; prevention of sexual transmission.

Figure 1.

A, Map of Health and Human Services Agency (HHSA) Regions of San Diego County. B, Map of human immunodeficiency virus (HIV) prevalence in San Diego County, by zip code based on 2010 US census data. C, Incident HIV Diagnoses in San Diego County. Annual incident HIV cases diagnosed by HHSA regions from 2006 to 2012. The HHSA East region data are not presented, because the numbers were too small. A decrease in the incident diagnosis rate is seen beginning approximately 2010.

Figure 2.

Identification of acute and early human immunodeficiency virus (HIV) infections through the Early Test explains reduction in new HIV diagnoses. Poisson regression was fit to incident cases and acute and early HIV diagnoses by the Early Test as an explanatory variable, and region and year as categorical covariates. Points represent observed incident diagnoses; solid lines, expected incident cases; and dotted lines, expected incidence (under the maximum likelihood parameter estimates) had there been no Early Test, and therefore no acute and early HIV diagnoses, for all years.

Figure 3.

A, Network geographic dynamics of human immunodeficiency virus (HIV) infection. Each zip code is color coded by net importation (ie, net export-green, net import-red) of HIV based on transmission dynamics of the San Diego Primary Infection Cohort. B, Zip code importation-exportation. Histogram demonstrating the distribution of zip codes in San Diego County in terms of their net importation of HIV. 92104 and 92103 have significantly higher net importation than all other zip codes (P = .002). Zip code 92103 is a clear outlier, >4 standard deviations from the mean.