Individuals whose HIV infection is
diagnosed late are making only a minimal contribution to the HIV epidemic, Danish
investigators report in the online edition of the Journal of Acquired Immune Deficiency Syndromes. Using
phylogenetic anaylsis, researchers were able to trace transmission clusters.
Only 20% of people diagnosed late were located within such a cluster.
However, the study’s findings provide
further evidence that people who have only recently been infected with HIV
are largely sustaining the spread of HIV. Almost all the transmission clusters
identified by the investigators involved young gay men, many of whom had
primary HIV infection.
HIV incidence has been stable in Denmark
over the past 20 years. There are approximately 300 new infections each year in
the country. Several studies have now shown that the majority of onward HIV
transmissions originate in individuals with undiagnosed infection. However, the
contribution of individuals whose HIV is diagnosed late (with a CD4 cell count below
200 cells/mm3) is currently unknown.
Investigators therefore conducted a study
involving the 1515 people newly diagnosed with HIV in Denmark after 2001.
Using a technique called phylogenetic analysis, the authors looked at networks
and clusters of HIV transmissions to see if they could identify the factors
that are driving the HIV epidemic in the country.
Approximately a fifth (260) of people were found to have primary HIV infection and 460 individuals were diagnosed
late. A total of 696 infections involved gay men.
The investigators identified a total of 46
transmission clusters involving 502 people.
“We found one third of the sequences from
newly diagnosed, treatment naïve patients formed 46 different phylogenetic
clusters visualising potential local epidemics,” comment the authors.
People within transmission clusters had a
significantly higher CD4 cell count (402 vs 287 cells/mm3, p <
0.001) and higher viral loads (63,000 vs 25,000 copies/ml, p < 0.05) than
individuals who could not be placed within transmission networks.
Half of all people with primary HIV
infection could be placed within a cluster, compared to only 22% of people whose HIV was diagnosed late.
“Individuals presenting with low CD4 T-cell
counts contribute less to the epidemic than individuals with higher CD4 T-cell
counts,” observe the researchers.
Age under 30, injecting drug use, primary
infection and sex between men were all significantly associated with being in a
cluster (p < 0.001).
Some 40 clusters involved gay men, and the
two largest transmission networks involved half of all people with primary
“Within 46 clusters we found primary HIV
sequences more frequently in larger clusters,” comment the investigators. They
believe this is “compatible with the increased infectiousness and transmission
potential….ascribed to primary HIV infection”.
Several of the clusters spanned the full
study period, “an explanation for the constant level of HIV diagnoses in
The study’s findings have implications for
HIV prevention. The authors recommend that efforts should be targeted at
younger gay men, especially those at risk of having primary infection. “Very
late presenters do not seem to be of significant importance from the
transmission standpoint. Efforts to identify very late presenters should be
enhanced for the benefit of the individual patient.”