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 stage	Duration	Transmission probability per act		Cofactor effects		Effects of HIV	Symptomatic (%)*
Infection and stage	Duration	M→F	F→M	STI on HIV	Lack of circumcision on HIV/STI†	Effects of HIV	M	F
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.
HIV
Primary	10 weeks	0.028	0.014		2	None
Asymptomatic	5 years	0.002	0.001		1	None
Symptomatic	4 years	0.006	0.003		1	HSV-2
AIDS	40 weeks	0.014	0.007		1	HSV-2
Chancroid	11 weeks	0.23	0.115	25	2		90	70
Gonorrhoea	14 weeks M, 14 weeks F	0.26	0.13	3	1		45	14
Chlamydia	14 weeks M, 52 weeks F	0.252	0.126	3	1		11	6
Syphilis
Primary	6 months	0.175	0.088	7.5	2		50	20
Early latent	1 year	0.018	0.009	1	1		0	0
Latent	2.5 years	0	0	1	1		0	0
Late latent	12.5 years	0	0	1	1		0	0
HSV-2
Primary	3 weeks	0.3	0.15	25	1
Early latent with recurrent ulcer‡	2 years	0.01	0.005	1	1	4
Latent with recurrent ulcer‡	10 years	0.005	0.003	1	1	4
Late latent	Lifelong	0	0	1	1	4
Recurrent ulcer substage	7 days	0.2	0.1	10	1	4	NA