Azithromycin resistance in Treponema pallidum in Reunion Island: A cross-sectional study

Since the beginning of the 21st century, Reunion Island has experienced a syphilis epidemic. Infected patients are mostly heterosexual, with a high proportion of women, suggesting that congenital syphilis is present on the island. To determine whether azithromycin can be used for mass treatment of syphilis on Reunion Island, we assessed the prevalence of macrolide resistance in Treponema pallidum (TP).

This monocentric cross-sectional study was conducted at the Reunion Island University Hospital. Samples were collected from lesions suggestive of primary or secondary syphilis. Samples positive for TP by multiplex polymerase chain reaction (PCR) were sent to the French National Reference Centre (NRC) for further analysis. Nested PCR-tpp47 was performed on these samples for detection of TP-DNA; 23s rRNA was amplified by PCR in confirmed positive samples. The Restriction Fragment Length Polymorphism (RFLP) technique was performed on samples with amplified 23s rRNA for detection of the A2058G mutation.

A total of 129 samples were collected from 119 patients. Of these, 18 tested positive for TP using multiplex PCR and were sent to the NRC. Fifteen (83.3%) of the 18 samples were confirmed positive by nested PCR-tpp47, and 23s rRNA was amplified in only 7 (38.9%) samples. Azithromycin resistance was detected in all TP strains with amplified 23s rRNA.

Amplification of 23s rRNA was successful in only 7 TP strains, all of which displayed resistance to macrolides. Keeping in mind the small sample size of our study, this suggests that azithromycin should not be used for mass treatment of syphilis in Reunion Island.