Table 1

 Parameter values for representation of natural history and transmission of HIV and sexually transmitted infections (STIs) for the Four Cities Study

Infection and stageDurationTransmission probability per actCofactor effectsEffects of HIVSymptomatic (%)*
M→FF→MSTI on HIVLack of circumcision on HIV/STI†MF
Durations are the same for males and females unless otherwise noted.
F, female; HSV-2, herpes simplex virus 2; M, male; NA, not applicable.
*Proportion of symptomatic STIs are defined for treatable STIs including gonorrhoea, chlamydia, chancroid and syphilis.
†Pertains to increased acquisition uncircumcised compared with circumcised, males only.
‡For HSV-2, recurrent ulcers occur at an average frequency of 2.5 months for males and three months for females in the early latent stage. For the latent stage, ulcers recur less frequently, every six months on average for males and every eight months on average for females.
    Primary10 weeks0.0280.0142None
    Asymptomatic5 years0.0020.0011None
    Symptomatic4 years0.0060.0031HSV-2
    AIDS40 weeks0.0140.0071HSV-2
Chancroid11 weeks0.230.1152529070
Gonorrhoea14 weeks M, 14 weeks F0.260.13314514
Chlamydia14 weeks M, 52 weeks F0.2520.12631116
    Primary6 months0.1750.0887.525020
    Early latent1 year0.0180.0091100
    Latent2.5 years001100
    Late latent12.5 years001100
    Primary3 weeks0.30.15251
    Early latent with recurrent ulcer‡2 years0.010.005114
    Latent with recurrent ulcer‡10 years0.0050.003114
    Late latentLifelong00114
    Recurrent ulcer substage7 days0.20.11014NA