HIV

HIV in STIsim is modeled with CD4-based disease progression through acute, latent, and late-stage phases, with ART treatment effects.

Class: sti.HIV | Alias: 'hiv' | Base class: BaseSTI

States and transitions

                        ┌─────────────┐
                        │ Susceptible │
                        └──────┬──────┘
                               │ infection
                               ▼
                        ┌─────────────┐
                        │    Acute    │  CD4 declines from ~800 to ~500
                        │  (~3 mo)   │  Transmissibility: 6x baseline
                        └──────┬──────┘
                               │
                               ▼
                        ┌─────────────┐
                        │   Latent    │  CD4 stable at ~500
                        │  (~10 yr)  │  Transmissibility: 1x baseline
                        └──────┬──────┘
                               │
                    ┌──────────┴──────────┐
                    │                     │
                    ▼                     ▼
             ┌─────────────┐       ┌─────────────┐
             │   Falling   │       │   On ART    │  CD4 reconstitutes
             │   (~3 yr)   │       │  (~18 yr)   │  Transmissibility: 0.04x
             │ 8x baseline │       └──────┬──────┘
             └──────┬──────┘              │ ART dropout
                    │                     ▼
                    │              ┌─────────────┐
                    │              │  Post-ART   │  CD4 declines linearly
                    │              └──────┬──────┘
                    │                     │
                    ▼                     ▼
             ┌─────────────────────────────────┐
             │          AIDS death             │
             │       (CD4 reaches 0)           │
             └─────────────────────────────────┘

Parameters

Natural history

Parameter	Default	Description
`cd4_start`	normal(800, 50)	Initial CD4 count at infection
`cd4_latent`	normal(500, 50)	CD4 count during latent phase
`dur_acute`	lognorm(3 mo, 1 mo)	Duration of acute infection
`dur_latent`	lognorm(10 yr, 3 yr)	Duration of latent infection (untreated)
`dur_falling`	lognorm(3 yr, 1 yr)	Duration of late-stage CD4 decline
`include_aids_deaths`	True	Whether to include AIDS mortality

Transmission

Parameter	Default	Description
`beta_m2f`	0.05	Per-act male-to-female transmission probability
`rel_beta_f2m`	0.5	Female-to-male transmission relative to male-to-female
`beta_m2c`	0.025/mo	Mother-to-child transmission probability
`rel_trans_acute`	normal(6, 0.5)	Relative transmissibility during acute phase
`rel_trans_falling`	normal(8, 0.5)	Relative transmissibility during late stage
`eff_condom`	0.9	Condom efficacy for reducing transmission

Initialization

Parameter	Default	Description
`init_prev`	0.05	Initial prevalence
`init_diagnosed`	0.0	Proportion initially diagnosed
`dist_ti_init_infected`	uniform(-120, -5)	Time of initial infection (months before start)

Treatment (ART)

Parameter	Default	Description
`art_efficacy`	0.96	ART efficacy at reducing transmission
`time_to_art_efficacy`	6 months	Time to reach full ART efficacy (linear ramp)
`art_cd4_growth`	0.1	Logistic growth rate for CD4 reconstitution on ART
`dur_on_art`	lognorm(18 yr, 5 yr)	Duration on ART before dropout

Care seeking

Parameter	Default	Description
`care_seeking`	normal(1, 0.1)	Relative care-seeking behavior (per agent)
`maternal_care_scale`	2	Multiplicative increase in care seeking during pregnancy