Impact of mass treatment on syphilis transmission: a mathematical modeling approach.

Background: Since 1997 Vancouver (British Columbia, Canada) has experienced an outbreak of heterosexually transmitted infectious syphilis, which prompted a mass treatment campaign in early 2000 in an attempt to control the disease. By 1 year postintervention, syphilis cases had rebounded significantly. We investigate the cause of this postintervention rebound.

Goal: We argue that the observed rebound postintervention may have been the result of the natural dynamics of disease transmission in an open population, in response to the partial application of mass treatment in the sexually active subgroup.

Study Design: We used a mathematical model that describes the transmission dynamics of syphilis in a population.

Results: The observed postintervention rebound is related to the mass treatment intervention.

Conclusion: Our results suggest that mass treatment may not be an optimal strategy to control the transmission of syphilis if complete coverage of high-frequency transmitters cannot be achieved and if population mobility is relatively high.