Abstract
Recent infection testing algorithms (RITA) for HIV combine serological assays with epidemiological data to determine likely recent infections, indicators of ongoing transmission. In 2016, we integrated RITA into national HIV surveillance in Ireland to better inform HIV prevention interventions. We determined the avidity index (AI) of new HIV diagnoses and linked the results with data captured in the national infectious disease reporting system. RITA classified a diagnosis as recent based on an AI < 1.5, unless epidemiological criteria (CD4 count <200 cells/mm3; viral load <400 copies/ml; the presence of AIDS-defining illness; prior antiretroviral therapy use) indicated a potential false-recent result. Of 508 diagnoses in 2016, we linked 448 (88.1%) to an avidity test result. RITA classified 12.5% of diagnoses as recent, with the highest proportion (26.3%) amongst people who inject drugs. On multivariable logistic regression recent infection was more likely with a concurrent sexually transmitted infection (aOR 2.59; 95% CI 1.04-6.45). Data were incomplete for at least one RITA criterion in 48% of cases. The study demonstrated the feasibility of integrating RITA into routine surveillance and showed some ongoing HIV transmission. To improve the interpretation of RITA, further efforts are required to improve completeness of the required epidemiological data.
Highlights
Between 2012 and 2016 the number of diagnoses of HIV in Ireland annually increased by almost 50% [1]
Sex between men was the reported probable route of transmission for 51.4% of cases, heterosexual transmission accounted for 27.6%, injecting drug use for 4.1% and the probable route of transmission was unknown for 15.2%
Regarding the completeness of surveillance data in 2016 and the criteria used in Recent infection testing algorithms (RITA), viral load was missing for 48% of cases, CD4 count for 31%, clinical stage for 30% and antiretroviral treatment (ART) history for 36%
Summary
Between 2012 and 2016 the number of diagnoses of HIV in Ireland annually increased by almost 50% (from 341 to 508) [1]. The significance of such an increase in a diagnosis-based HIV surveillance system, as exists in Ireland, is difficult to interpret. Primary prevention of HIV through a reduction in transmission is a key goal within the HIV continuum of care and HIV surveillance should ideally monitor current transmission in order to evaluate and inform public health action. While HIV incidence is the ideal indicator to monitor HIV transmission, it is not readily or reliably directly measurable. The proportion of recent HIV infections in a population is an alternative indicator of ongoing HIV transmission and can be used to estimate incidence [3]. Recent infection testing algorithms (RITA) use a laboratory test, or a combination of laboratory tests and supplementary laboratory and clinical information, to classify an HIV infection as likely recently acquired or as longstanding [3]
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