RESUMO
<p><b>OBJECTIVE</b>To determine the relationship between the rate of condom use and incidence of Chlamydia amongst commercial sex worker, using a mathematical model.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>When k remains constant, this mathematical model reflects the qualitative relationship between the rate of condom use and the incidence of Chlamydia.</p>