EMERGING PATTERNS OF HIV TRANSMISSION - THE VALUE OF ALTERNATIVE SURVEILLANCE METHODS

Objective: To assess the current patterns of HIV transmission in Los A ngeles County and determine if AIDS surveillance data accurately refle ct these patterns. Design: Records-based cohort study. Methods: The de mographic and HIV risk characteristics of persons considered to be rec ently infected with HIV (CD4+ count >700x10(6)/I) were determined and compared with the characteristics of persons meeting the Centers for D isease Control and Prevention (CDC) 1993 AIDS case definition. Data we re obtained for patients with HIV infection enrolled from four HIV out patient clinics and analyzed between August 1991 and July 1993. Result s: The patient cohort included 1857 persons with HIV infection; 1096 ( 59.1%) met the CDC 1993 AIDS case definition and 134 (7.2%) had a CD4 lymphocyte count >700x10(6)/I. The median CD4+ count for the group pr esumed to be recently infected was 809x10(6)/I. Persons considered rec ently infected with HIV were more likely than those meeting the AIDS c ase definition to be female (26.1 and 14.5%, respectively; P<0.001), b lack (28.4 and 18.2%, respectively; P=0.001), or male homosexual injec ting drug users (IDU; 6.7 and 3.4%, respectively; P=0.05). After contr olling for confounding variables by logistic regression, persons recen tly infected were more likely to be female [adjusted odds ratio (OR), 3.4; 95% confidence interval (Cl), 1.8-6.5; P<0.001], black (adjusted OR, 1.6; 95% Cl, 1.1-2.5; P=0.02) or male homosexual IDU (adjusted OR, 2.4; 95% Cl, 1.1-5.2; P=0.02) than persons with AIDS. Conclusions: Ou r results suggest that the HIV epidemic in Los Angeles County is curre ntly advancing into different subpopulations and indicate that the cur rent patterns of HIV transmission in the County are not fully reflecte d in standard AIDS surveillance activities. However, our data must be interpreted cautiously because of potential selection and misclassific ation biases. These findings illustrate the benefits of alternative su rveillance mechanisms in detecting important changes in HIV transmissi on and defining groups at risk, especially in jurisdictions without HI V reporting.