Experimental gonococcal urethritis and reinfection with homologous gonococci in male volunteers.

Background: Reinfection, a common occurrence with gonorrhea, may result from a lack of protective immune response, or from the tremendous gonococcal strain variation.
Goal: A two-phase study in human volunteers tested whether experimental infection with Neisseria gonorrhoeae MS11mkC would protect against reinfection with the same organisms.
Study Design: In phase 1, an intraurethral inoculum of 57,000 piliated, transparent (opacity protein-negative [Opa-]) MS11mkC N gonorrhoeae infected 14 of 15 (93%) volunteers. The volunteers were encouraged to delay treatment for at least 5 days. In phase 2, which began 2 weeks after treatment for the initial infection, volunteers were inoculated with 7,100 piliated, Opa- MS11mkC.
Results: The phase 2 challenge infected 6 of 14 (43%) previously infected volunteers and 5 of 10 (50%) naïve control subjects. Phase 1 volunteers who resisted reinfection were significantly more likely to have had a fourfold or greater increase in lipooligosaccharide immunoglobulin G during phase 1 than those who did not resist reinfection (P = 0.026).
Conclusions: Although infection did not provide protection from reinfection under the conditions used, the results suggest that immunity to reinfection is more complex than anticipated by the experimental design.