Treponema pallidum macrolide resistance in BC

Since mid-1997 British Columbia has experienced an outbreak of syphilis, initially in heterosexuals and more recently among men who have sex with men (MSM). Starting in 1999, primarily in patients presenting to the sexually transmitted diseases clinic at the BC Centre for Disease Control (BCCDC), moist lesions of primary and secondary syphilis were swabbed for polymerase chain reaction (PCR) testing for Treponema pallidum. The PCR method used was polA gene amplification using a CDC protocol.1

When the question of azithromycin resistance arose in 2004, specimens were examined retrospectively for the mutation in the T. pallidum 23sRNA gene in collaboration with investigators from the University of Washington.2

From 2000–2003, 1 of 47 positive PCRs showed resistance in a travel- acquired heterosexual case. In 2004, 4 of 9 positive PCRs showed the resistant gene, all in MSM.

The 23sRNA gene correlated with clinical resistance to azithromycin in Dublin and San Francisco.2

All of the BC patients received penicillin G benzathine or doxycycline; therefore, treatment failure with azithromycin was not tested.

Treatment of choice in BC for early syphilis is one dose of penicillin G benzathine (2.4 MU intramuscularly). Oral doxycycline therapy (100 mg twice daily for 2 weeks) is a second-line treatment, with oral azithromycin therapy (one 2-g dose) as a third-line treatment, especially in noncompliant patients who refuse injections. This sequence is in compliance with the Canadian and US STD treatment guidelines.3^,4

In a recent study in Africa, a 2-g oral dose of azithromycin was as effective as a 2.4-MU intramuscular dose of penicillin G benzathine.5 However, in developed countries, because of resistance trends, azithromycin should be reserved as a third-line treatment for early syphilis, and patients thus treated should be followed closely, both serologically and clinically.