docs: api: clean up intro, related: #3, #5

docs/api/intro.tex

@@ -3,18 +3,11 @@ \section{Introduction}
 As of 2019, two thirds (25.7 million) of all people living with HIV globally
 were in Sub-Saharan Africa (SSA), where
 an estimated one million new HIV infections were acquired in 2019 \cite{AIDSinfo}.
-Data suggest that key populations, including individuals engaged in sex work and men who have sex with men,
-experience disproportionate risks of HIV acquisition and onward transmission in SSA
-\cite{Baral2012,Beyrer2012,Mishra2012,Boily2015}.
 HIV treatment to reduce onward transmission remains a key element of combination HIV prevention \cite{WHO2016ART}.
-Effective HIV treatment with antiretroviral therapy (ART) leads to viral load suppression
-and has been shown to prevent HIV transmission between sex partners \cite{Lundgren2015,Danel2015,Cohen2016}.
-\par
 Following empirical evidence of partnership-level efficacy of ART
-in preventing HIV \cite{Lundgren2015,Danel2015,Cohen2016},
+in preventing HIV transmission \cite{Lundgren2015,Danel2015,Cohen2016},
 and model-based evidence of ``treatment as prevention'' \cite{Granich2009,Eaton2012,Cori2014},
-several large-scale community-based trials of universal test-and-treat (UTT)
-were recently completed \cite{Iwuji2018,Havlir2019,Hayes2019}.
+several large-scale community-based trials of universal test-and-treat (UTT) were recently completed.
 These trials found that over 2-to-4 years,
 cumulative incidence under UTT did not significantly differ from
 cumulative incidence under ART according to national guidelines \cite{Havlir2019,Hayes2019,Iwuji2018}.
@@ -28,11 +21,18 @@ \section{Introduction}
 21--54\% of study participants remained unsuppressed \cite{Iwuji2018,Havlir2019,Hayes2019}.
 Populations experiencing barriers to viral suppression under UTT
 may be at highest risk for acquisition and onward transmission, including key populations like
-sex workers and men who have sex with men \cite{Hakim2018,Nyato2019},
-as well as youth, and heterosexual men \cite{Green2020,Quinn2019}.
+sex workers and men who have sex with men \cite{Hakim2018,Nyato2019}.
+Other sub-populations, including youth and heterosexual men, also
+experience barriers to engagement in ART care \cite{Green2020,Quinn2019}
+that could undermine treatment as prevention.
 While widespread UTT scale-up may fill some coverage gaps,
 equitable access to ART for all populations remains an open challenge.
 \par
+Risk heterogeneity, defined by various factors affecting acquisition and onward transmission risk,
+is a well-established determinant of epidemic persistence and controllability
+with a basis in the modelling literature \cite{Anderson1986,Boily1997}.
+Model comparison studies by \citet{Hontelez2013} and \citet{Rozhnova2016}
+found that projected prevention impacts of ART scale-up were smaller with greater heterogeneity.
 Given the upstream and complementary role of transmission modelling
 in estimating the prevention impacts of ART \cite{Eaton2012,Delva2012},
 we sought to examine how heterogeneity in risk and ART uptake has been represented