Real-time polymerase chain reaction shows that density centrifugation does not always remove Chlamydia trachomatis from human semen

Objective: To evaluate the efficiency of sperm washing procedures to remove Chlamydia trachomatis from semen both in clinical samples and experimental inoculations. Design: Laboratory-based study. Setting: Research laboratory in a university hospital. Patient(s): One hundred men attending for diagnostic semen analysis as part of infertility investigations and three sperm donors providing ejaculates for research purposes. Main Outcome Measure(s): Number of DNA copies of C. trachomatis, infectivity in an HeLa cell monolayer, and immunofluorescence. Result(s): Of the 100 semen samples examined, 13 contained detectable levels of C. trachomatis DNA (675–15,920 copies/mL) and in only 7 was this completely removed after sperm washing. In the remaining six DNA-positive samples, the number of copies in the postwash preparation ranged from 36–455 per mL. Experimental inoculations found that postwash preparations containing C. trachomatis DNA as low as 61 copies/mL were able to establish an infection in vitro. Conclusion(s): Undiagnosed C. trachomatis infections in men attending for assisted conception could potentially lead to infection or contamination of the IVF culture system as sperm washing methods are not 100% effective