NEW YORK (Reuters Health) - Despite the initial apparent success of a program to control Chlamydia trachomatis in British Columbia, there are now more cases than there were before the intervention, Canadian researchers report in the November 15th issue of the Journal of Infectious Diseases. This may be a product of reduced natural immunity and subsequent reinfection.

"The current strategy for Chlamydia control based on case finding, screening, treatment and contact tracing may be unexpectedly affecting the epidemiology of Chlamydia by interfering with the development of natural immunity," lead investigator Dr. Robert C. Burnham told Reuters Health.

Dr. Burnham and colleagues at the University of British Columbia Centre for Disease Control, Vancouver and colleagues note that in 1991, the case rate was 216 per 100,000. By 1997, after introduction of control measures, the rate fell to 104 cases per 100,000. However, since 1998, rates began to rise and are now greater than they were before inception of the program.

The researchers hypothesized that because treatment was taking place at increasingly earlier times after acquisition of the pathogen, it interfered with immunity induced by the infection. Certain human and mouse studies support this notion.

Indeed, analysis showed that the relative risk of reinfection had increased by 4.6% since 1989. The increase was greatest in young women. Moreover, a mathematical model mirrored the findings, showing an early reduction in prevalence, followed by a rebound.

"The results suggest that a vaccine rather than antibiotics may be necessary to ultimately control this common infectious disease," Dr. Burnham concluded.

J Infect Dis 2005;192:1836-1844

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