[An assessment on the effectiveness of condom use in reducing the incidence of chlamydia through mathematical modelling].
OBJECTIVE
To determine the relationship between the rate of condom use and incidence of Chlamydia amongst commercial sex worker, using a mathematical model.


METHODS
Assuming that p(%) is the rate of condom use by female sex workers, and r(%) is the incidence of Chlamydia. If the use of condom increases by delta p, then the incidence of Chlamydia will decrease by delta r. k is the relative rate of change. Then, the mathematical model established becomes dr/dp = -kr.


RESULTS
The solution of the differential equation is r (p) = r (P0) exp [-k (p - p0)]. Using the surveillance data gathered from 100% Condom Use Program in Wuhan City, the k value is calculated to be 4.36. If k indicates the contribution coefficient of reducing Chlamydia after condom use, when the rate of condom use increases by 16%, then the incidence of Chlamydia will decrease by 50%. The average difference between the actual incidence and the incidence calculated from the mathematical model is only 6.2%. This result demonstrates a good fit. The predicted result of using this mathematical model shows that at the time of lower levels of condom use, a small increment on the rate of condom use would considerably reduce the infection rate of Chlamydia.


CONCLUSIONS
When k remains constant, this mathematical model reflects the qualitative relationship between the rate of condom use and the incidence of Chlamydia.
Wei
Shan-bo
SB
Department of Social Medicine, Tongji Medical College of Huazhong, University of Science and Technology, Wuhan 430030, China. shanbowei@whcdc.org
Lu
Jun-an
JA
Chen
Ji-nan
JN
Lu
Zu-xun
ZX
D002681:China / Q000453:epidemiology; D002690:Chlamydia Infections / Q000453:epidemiology* / Q000517:prevention & control*; D017280:Condoms / Q000706:statistics & numerical data*; D005544:Forecasting; D006801:Humans; D015994:Incidence; D008962:Models, Theoretical; D011159:Population Surveillance; D011477:Sex Work