A modified community viral load measure to support the evaluation of transmission potential of HIV in the population: a retrospective cohort study

Abstract

BackgroundPopulation viral load is a conceptual measure involving the summation of viral load of all HIV-positive individuals, the estimation of which is complex. As an alternative, community viral load is a simpler measure, but its determination is restricted to individuals diagnosed with HIV only. We proposed a new measure and piloted its use with clinic data collected in Hong Kong Special Administrative Region, China. MethodsAnonymous longitudinal data of all HIV-positive individuals attending HIV specialist clinics in the public service in Hong Kong were obtained retrospectively. By back-calculation, we estimated each person's seroconversion time, followed by the construction of viral load curves from seroconversion to diagnosis. Annual full community viral load, a measure modified from community viral load, was then estimated by the summation of viral loads of both diagnosed and undiagnosed HIV-positive individuals. The study was approved by the research ethics committees of Joint Chinese University of Hong Kong–New Territories East Cluster, Kowloon East/Central Cluster, Kowloon West Cluster, and Department of Health. Data access was granted by the Department of Health, Hong Kong Special Administrative Region Government in compliance with the Personal Data (Privacy) Ordinance. Findings61 043 viral load measures were obtained from 4514 HIV-positive individuals aged 18 years or older to determine full community viral load between 1985 and 2006. 3747 (83%) individuals were men and 3250 (72%) were Chinese, with sexual transmission accounting for the disease in 4056 (90%) patients. The median interval from estimated seroconversion to diagnosis was 6 years (IQR 3–7 years). Between 1997 and 2004, the annual full community viral load was 6–10 times higher than the community viral load. Since 1991, full community viral load had risen sharply, which was mainly contributed by heterosexual male in 1991–95 followed by men who have sex with men in 1996–2004. Injection drug users contributed to less than 10% of viral load burden in epidemiology curves. Overall, the growth curve of full community viral load was about 5 years ahead of other viral load measures. InterpretationIn epidemiological surveillance, full community viral load can be a surrogate of population viral load in the community. Construction of full community viral load curves allows timely assessment of HIV transmission to be made ahead of conventional epidemiology curves derived from reported incidence. FundingThe study was supported by a grant approved by the Council for the AIDS Trust Fund, Hong Kong Special Administrative Region Government (project code MSS229R). NSW is supported by Guangdong Provincial Centers for Skin Diseases and STI Control, and by the South China UNC STD Research Training Center grant (number 1D43TW009532-01).