Unstable housing may be responsible
for up to one in five new infections with HIV or hepatitis C among people who inject drugs in the United
Kingdom and the United States, a global modelling study has found.
The modelling exercise, published in the journal The Lancet
Public Health, was carried out by a team from the University of Bristol.
A systematic
review and meta-analysis of 37 studies published in 2021 showed that unstable
housing increased the risk of hepatitis C infection by 64% and HIV infection by
39% in people who inject drugs.
The study investigators say that unstable housing – homelessness
or lack of a fixed home – is likely to increase the risk of acquiring HIV or
hepatitis C in several ways. People with unstable housing may prioritise other
survival needs over measures to avoid HIV or hepatitis C or may lack places to
store sterile injecting equipment. They may also face barriers in accessing
medical services. Studies have also shown that people with unstable housing are
more likely to be involved in sex work and to have a greater number of
injecting partners.
Following the findings of the systematic review, the University
of Bristol team developed a model to assess what proportion of new HIV and
hepatitis C infections are attributable to unstable housing – the population attributable
fraction – and to identify the countries in which unstable housing in people
who inject drugs has the greatest impact on new HIV and hepatitis C infections.
The model of transmission was adjusted to take into account
the uptake of antiretroviral therapy in various countries as well as the
average duration of unstable housing and injecting drug use. The rate of
transmission depended on HIV or hepatitis C prevalence in people who inject drugs by
country or region. It was adjusted for the rates of transmission estimated in
people with unstable housing, derived from the 2021 meta-analysis.
The model projected estimates for 56 countries with
sufficient data on hepatitis C and HIV prevalence as well as the housing status of people
who inject drugs.
Estimates for HIV transmission were available for 50 countries.
Overall, unstable housing will account for 7.9% of new HIV infections in people
who inject drugs between 2020 and 2029.
Estimates for hepatitis C transmission were available for 49 countries.
Overall, unstable housing will account for 11.2% of new hepatitis C infections
in people who inject drugs between 2020 and 2029.
The impact of unstable housing on HIV and hepatitis C transmission
is greatest in high-income countries. Unstable housing will account for 21% of
new HIV infections and 26% of new hepatitis C infections between 2020 and 2029
in North America. In comparison, unstable housing will account for 6% of new HIV
infections and 8% of new hepatitis C infections in lower- and middle-income
countries.
However, a small number of countries contribute
disproportionately to the global total. Six countries – Afghanistan, the Czech
Republic, England, India, the United States and Wales – will account for 29% of
global HIV infections and 44% of global hepatitis C infections attributable to unstable
housing in people who inject drugs. In each country, unstable housing will
contribute more than 20% of new HIV and hepatitis C infections in people who
inject drugs between 2020 and 2029.
Those countries contributing most to the global burden of
new infections in the unstably housed have a high prevalence of unstable
housing in people who inject drugs. More than 40% of people who inject drugs
are estimated to be unstably housed in the Czech Republic, England and the
United States compared to Russia (4%) or China (8%). The study authors say that
social protection may explain this difference and may therefore prove “an important
determinant of the contribution of unstable housing to HIV and hepatitis C
transmission among people who inject drugs.”
“With the UNAIDS beginning to incorporate social enablers
into their target setting, including for key populations, it is essential to
strive for improved access to stable housing for people who inject drugs,” they
advocate. “HIV and HCV elimination targets will be missed unless the effect of
these structural drivers [is] mitigated.”
However, the study authors say it is unlikely stable housing
alone will be sufficient to eliminate the excess risk observed in this study. “Interventions
must go beyond simply providing stable housing by addressing individuals’ broader
health and social needs and providing access to prevention and treatment
services.”