Monday, February 1, 2016

How Many People Are Living with Undiagnosed HIV Infection? An Estimate for Italy, Based on Surveillance Data

To estimate the size and characteristics of the undiagnosed HIV population in Italy in 2012 applying a method that does not require surveillance data from the beginning of the HIV epidemic.

We adapted the method known as "London method 2"; the undiagnosed population is estimated as the ratio between the estimated annual number of simultaneous HIV/clinical AIDS diagnoses and the expected annual progression rate to clinical AIDS in the undiagnosed HIV population; the latter is estimated using the CD4-count distribution of asymptomatic subjects reported to surveillance. Under-reporting/ascertainment of new diagnoses was also considered. Also, the total number of PLWHIV was estimated.

The undiagnosed HIV population in 2012 was 13,729 (95%CI: 12,152-15,592), 15,102 (13,366-17,151) and 16,475 (14,581-18,710), assuming no under-reporting/ascertainment, 10% and 20% of under-reporting/ascertainment, respectively. The percentage of undiagnosed cases was higher among HIV people aged <25 years (25-28%), MSM (16-19%) and people born abroad (16-19%), while is small among injection drug users were (3%).

The estimate of people in Italy with undiagnosed HIV in 2012 was in a plausible range of 12,000-18,000 cases, corresponding to 11-13% of the overall prevalence. The method is straightforward to implement only requiring annual information from the HIV surveillance system about CD4-count and clinical stage at HIV diagnosis. Thus, it could be used to monitor if a certain prevention initiative lead to the reduction of the undiagnosed HIV population over time. It can also be easily implemented in other countries collecting the same basic information from the HIV surveillance system.

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  • 1"L. Spallanzani" National Institute for Infectious Diseases, IRCCS, Rome, Italy bIstituto Superiore di Sanità, Rome, Italy. 

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