Screen more or screen more often? Using mathematical models to inform syphilis control strategies

Tuite, Ashleigh R; Fisman, David N; Mishra, Sharmistha

doi:10.1186/1471-2458-13-606

BMC Public Health

Table 1 Model parameters

From: Screen more or screen more often? Using mathematical models to inform syphilis control strategies

Parameter	Details	Value	Distribution	Source
Parameter	Details	Value	Type	Source
Population characteristics
Population size		2,000
Time spent in model (years) (min, max, mode)		1, 34, 17	Triangular	[27]; assumption
Proportion of MSM who are HIV positive		0.2		[29]; assumption
Syphilis natural history
Probability of transmission (per act) (min, max, mode)	Penile-anal/Penile-oral	0.01, 0.05, 0.014	Triangular	[26]; assumption
Incubation period (days)		21-28	Uniform discrete	[30]
Infection/infectious period (days)				[16, 31, 32]
	Primary	45-60	Uniform discrete
	Secondary	100-140	Uniform discrete
	Early latent*	365
	Recurrent	90
	Late Latent*	Until end of life in model
Probability of recurrent syphilis		0.25		[33]
Duration of protective immunity following				[21, 34, 35]
treatment (years)				[21, 34, 35]
	Primary or secondary syphilis	0
	Latent syphilis	5
Partnership characteristics
Number of partners in past 6 months (proportion of population in each category)				[27]
	1	0.28
	2-9	0.48
	10-29	0.15
	30-75	0.09
Maximum number of partnersin past 6 months (by partner number category) (min, max, mode)
	1	1		Assumption
	2-9	2,9,8	Triangular
	10-29	10,29,25	Triangular
	30-75	30,75,50	Triangular
Duration of partnership (days) (min, max, mode)				[27]; Assumption
	Casual	1,2,1	Triangular
	Regular	7,3000,365	Triangular
Behavioural characteristics
Frequency of anal sex (per day)				[26]
	Casual partnership	0.7
	Regular partnership	0.3
Frequency of oral sex (per day)				[26]
	Casual partnership	1
	Regular partnership	0.3
Probability of condom use (anal sex)				[2, 27]
	HIV-concordant	0.5
	HIV-discordant	0.8
Condom efficacy	Assume condom use for anal intercourse only	0.9		[36]
Test and Treatment characteristics
Probability of seeking medical care for symptoms				[19, 37]
	Primary	0.25
	Secondary	0.60
Time to treat (days)	Primary	3-56	Uniform	[38]; assumption
	Secondary	1-57	Uniform
Proportionof population screened routinely for				[19, 24, 39, 40];
syphilis				assumption
	HIV positive	0.5
	HIV negative	0.2
Test sensitivity	Treponemal-specific screening test	0.95		[41, 42]
Probability of partner notification				Assumption
	Casual partner	0.1
	Regular partner	0.6
Trace-back period for partner notification				[43]
(months)				[43]
	Primary	3
	Secondary	6
	Early latent	12
Time from index case identification to screening of named partner(s) (days)		3-21		Assumption

*Not infectious.

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ISSN: 1471-2458

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