Almost half of all new HIV transmissions in
the US originate in individuals who are unaware that they are HIV-positive, a
modelling study published in the online edition of AIDS estimates.
Only 20% of HIV infections in the US are
undiagnosed, but the investigators calculated that they were the source of
49% of all new onward transmissions.
“Decreasing the number of persons unaware
of their infection must remain a priority goal of HIV prevention efforts,”
comment the authors.
With appropriate treatment and care the
prognosis of many HIV-positive patients is now normal. Virologically
suppressive antiretroviral therapy also has wider public health benefits,
reducing the risk of HIV transmission by 96%.
Late diagnosis is the principal factor
underlying much of the HIV-related mortality that continues to be seen in
resource-rich countries. Several studies have also suggested that a
disproportion amount of new HIV transmissions have their source in undiagnosed
Testing is therefore a cornerstone of
efforts to control HIV. Opt-out HIV testing is now recommended in the US for
adolescents and adults aged between 13 and 64 years as part of their routine
health care. Screening at least annually is recommended for patients with higher
risk of the infection.
Previous research has suggested that HIV
transmission rates in the US are 3.5 times higher for undiagnosed individuals
compared to patients whose infection has been diagnosed.
Investigators updated the information used
to arrive at this estimate, taking into account revised estimates of the
proportion of undiagnosed infections and the impact of virologically
suppressive HIV therapy on infectiousness.
The model was based on HIV prevalence rates
in 2008 and HIV incidence between 2006 and 2009. The proportion of HIV-positive
individuals unaware of their infection was 20%, and 39% of patients had a viral
load below 400 copies/ml. Other variables included in the model were estimates
of the frequency of unprotected sex with HIV-negative partners. The model also
took account of the proportion of patients who were successfully linked to HIV
care and retained in care.
An estimated 49% of all new transmissions
were from individuals who were unaware of their infection status.
If the proportion of diagnosed patients with
a viral load below 400 copies/ml increased to 60%, this increased the burden of
new transmissions attributed to undiagnosed individuals to almost 60%.
“Increasing the percentage with viral
suppression substantially reduced the percentage of transmissions form persons
aware of their infection,” comment the authors. “The impact could be even
further strengthened with implementation of revised recommendations for
antiretroviral treatment for patients with CD4 cell count below 500 cells/mm3,
or even higher.”
The transmission rate for patients aware of
their infection status varied between 1.8 and 2.7 per 100 persons. It was
between three and seven times higher for undiagnosed individuals (9.2 to 12.6
per 100 persons).
In a scenario when 39% of HIV-positive
patients had a viral load below 400 copies/ml, then each increase of 100 in the
number of diagnosed infections was estimated to avert eight new transmissions.
However, simply reducing the number of
undiagnosed infections is not enough in itself to control the HIV epidemic. The
authors stress that patients then have to be promptly connected with a
specialist clinic, retained in care and achieve virological suppression.
“While current estimates of the percentage
of persons diagnosed with HIV who are linked to care are relatively high (69%
to 82%), the percentage of persons retained in care is much lower (45% to 59%)
and estimates of the percentage with viral suppression range from 24% to 39%
for those who are aware of their infection.”
The authors conclude: “Additional efforts
are needed to educe the number of people unaware of their infection…reduce
transmission rates, and improve linkage and retention in care and viral