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Diagnosis of Early HIV Infections May Have Contributed to Fall in Incidence in San Diego


An HIV testing program targeting individuals with acute or early infection likely contributed to a decline in incident or new infections in San Diego after 2008, investigators report in the May 11 online edition of Clinical Infectious Diseases. The Early Test initiative involved negative HIV antibody tests being rescreened using nucleic acid testing (NAT) -- a technique capable of detecting new HIV infections within 7-10 days after exposure.

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A fall in new HIV diagnoses was observed in proportion to the number of acute/early infections diagnosed. Moreover, molecular analysis showed that transmission networks were more likely to terminate in the zip codes where the testing campaign was marketed.

"Our analyses demonstrated that the observed decrease in incident diagnoses was associated with the steady increase in testing by the Early Test program," commented the authors.

Over 1 million individuals in the U.S. are living with HIV and there are around 50,000 new diagnoses each year. Between a third and a half of all new infections are thought to originate from individuals recently infected with HIV. Acute, early, or primary HIV infection is characterized by a very high viral load, meaning that people at this stage are potentially very infectious to their sexual partners. Moreover, most people with this phase of HIV infection are usually unaware that they have been infected with the virus.

Diagnosing patients with acute or early HIV is therefore a public health priority. In 2007, the Early Test program was introduced in San Diego. Its marketing targeted men who have sex with men (MSM) living in the central area of the city, especially in zip codes 92103 and 92104, which are at the center of the San Diego gay community, including the Hillcrest neighborhood.

Investigators designed a study to evaluate the impact of this testing program on trends in local HIV incidence. To do this, they used epidemiological, geographic, and molecular sequencing information.

Between 2006 and 2012, an average of 471 new HIV diagnoses were made each year in San Diego County. The distribution of the number of diagnoses between the 6 local health areas in the county remained stable during this period. The central region consistently had the highest HIV prevalence, and within the central region the zip codes 92103 and 92104 had the highest prevalence rates (5.7% and 4.0%, respectively). 

The Early Test program conducted 20,111 tests and made 460 diagnoses by the end of 2012.

Infections were defined as "acute" if the patient lacked antibodies against HIV but had a positive NAT result, and as "early" if they were antibody positive and had serological and virological characteristics consistent with infection for 6 months or less.

Each year between 2008 and 2012 the program diagnosed an average of 17 acute (19.6% of all diagnoses) and 21 early (24.3% of all diagnoses) infections.

During this period, 171 people in the 92103 and 92104 zip codes were diagnosed by the program and evaluated for recent infection; 54% of these infections were either acute or early (22% acute).

People living in the 92103 and 92104 zip codes were more significantly likely to be diagnosed with acute or early infection compared with residents elsewhere in San Diego (54% vs 44%; p = 0.04).

The investigators used new diagnoses as a proxy for HIV incidence and assumed that the rate of new infections was driven by factors including, region, year, the number of tests performed by the Early Test program, and the number of infections it detected.

They found that the number of tests performed by the program was positively associated with a significant reduction in HIV incidence (p < 0.001).

Other possible reasons for this decline in the rate of new infections were discounted by the authors. These included a reduction in sexual risk (rates of sexually transmitted infections increased in the study period), more effective HIV therapy (there was a significant increase in the number of ART-treated patients in San Diego who experienced virological failure during the period of analysis), national incidence trends, or the availability of pre-exposure prophylaxis (PrEP).

Molecular sequencing enabled the investigators to identify transmission networks involving patients diagnosed with acute or early infection. They calculated the net direction of HIV transmission, into or out of specific zip codes. Compared to all other zip codes, 92103 and 92104 had the highest net importation, whereas several other zip codes had the highest next exportation.

"This suggested," wrote the investigators, "increased HIV transmission chain termination in the 92103 and 92104 zip codes, areas targeted by the Early Test program."

Individuals living in zip codes 92103 and 92104 were more likely to be diagnosed with acute or early infection compared to residents of other areas (34.2% vs. 27.3%), suggesting that people living in areas other than those targeted by the Early Test program had a delay between infection and diagnosis. However, there was no difference in the time between diagnosis and initiation of HIV therapy between patients in the 2 central zip codes and patients living in other areas.

"These results support the hypothesis that the Early Test program targeted at MSM living in 92013 and 92014 zip codes led to increases in the diagnosis of [acute and early HIV] infection and may help explain the observed decrease in incident HIV diagnoses in the Central region," commented the authors.

They concluded, "early HIV diagnoses by the primary infection screening program probably contributed to the observed decrease in HIV incident diagnoses in San Diego since 2008 and suggest that testing programs, which can diagnose AEH infection, should be expanded among high-risk populations."



SR Mehta, B Murrell, CM Anderson, et al. 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. Clinical Infectious Diseases. May 11, 2016 (online ahead of print).

Other Source

Infectious Diseases Society of America. HIV testing during early infection may reduce new cases in high-risk communities. Press release. May 12, 2016.