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Successful diagnosis of acute/early HIV infections may have contributed to fall in HIV incidence in San Diego
Michael Carter, 2016-05-17 14:40:00
An HIV testing
programme targeting individuals with acute/early infection likely contributed
to a decline in incident infections in San Diego after 2008, investigators
report in Clinical Infectious Diseases.
The “Early Test” initiative was launched in 2007 and involved negative HIV
antibody tests being re-screened using nucleic acid testing (NAT) – a technique
capable of detecting HIV infections within 7-10 days after exposure. 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.
initiative was targeted at men who have sex with men (MSM) living in specific
zip codes in the central San Diego area.
demonstrated that the observed decrease in incident diagnoses was associated
with the steady increase in testing by the Early Test program,” comment the
Over 1 million
individuals in the United States are infected with HIV and there are 50,000 new
diagnoses each year. Between a third and a half of all new infections are
thought to originate in individuals recently infected with HIV. Acute/early/primary
HIV infection is characterised by a very high viral load, meaning that patients
are potentially very infectious to their sexual partners. Moreover, most
patients with this phase of HIV infection are usually unaware that they have
been infected with the virus.
patients with acute/early HIV is therefore a public health priority. In 2007,
the Early Test programme was introduced in San Diego. Its marketing targeted
MSM living in the central area, especially zip codes 92103 and 92104.
designed a study to evaluate the impact of this testing programme 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 six 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%,
respectively). These zip codes are at the centre of the San Diego gay
The Early Test
programme conducted 20,111 tests and made 460 diagnoses by the end of 2012.
defined as acute if the patient lacked antibodies but had a positive NAT result,
and as early if they were antibody positive and had serologic and virologic
characteristics consistent with infection for six months or less.
Each year between
2008 and 2012 the programme diagnosed an average of 17 acute (19.6% of all
diagnoses) and 21 early (24.3% of all diagnoses) infections.
period, 171 people in the 92103 and 92104 zip codes were diagnosed by the programme
and evaluated for recent infection; 54% of these infections were acute or early (22% acute).
Patients living in
the 92103 and 92104 zip codes were more likely to be diagnosed with acute/early
infection compared with residents elsewhere in San Diego (54% vs. 44%, p =
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 programme and the number of infections it
They found that
the number of tests performed by the programme was positively associated with a
significant reduction in HIV incidence (p < 0.001).
reasons for this fall 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 virologic failure during the period of analysis),
national incidence trends or the availability of pre-exposure prophylaxis
sequencing enabled the investigators to identify transmission networks
involving patients diagnosed with acute/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.
write the investigators, “increased HIV transmission chain termination in the
92103 and 92104 zip codes, areas targeted by the Early Test program.”
in zip codes 92103 and 92104 were more likely to be diagnosed with acute/early
infection compared to residents of other areas (34.2% vs. 27.3%), suggesting that
patients living in areas other than those targeted by the Early Test programme
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 two central zip codes and patients living in other areas.
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 AEH [acute and
early HIV] infection and may help explain the observed decrease in incident HIV
diagnoses in the Central region,” comment the authors.
They conclude, “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.”