Haemophilus ducreyi (HD) and Treponema pallidum subsp. pertenue (TP) are major causative agents of cutaneous ulcers (CU) in the tropics. Azithromycin is recommended to treat sexually transmitted HD infections and has good in-vitro activity against HD strains from both genital and skin ulcers. We investigated the efficacy of single oral dose azithromycin on HD-CU.

We conducted a community-based cohort study in Lihir Island, Papua New Guinea, from October 2014 through May 2016. Consenting patients with skin ulcers >1cm in diameter were eligible for this study and had collected a lesional swab for PCR. All participants were treated with single-dose azithromycin (30mg/Kg) and were followed-up for assessment of clinical resolution. We retrospectively classified patients according to PCR results into HD, TP, and PCR-negative groups. The primary endpoint was healing rates of HD-CU at 14 days after treatment.

We obtained full outcome data from 246 patients; 131 (53%) were HD PCR-positive, 37 (13.5%) were TP positive and 78 (28.5%) were negative for all tests. Healing rates were 88.5% (95%CI 0.81–0.92) in the HD group, 78.3% (0.62–0.88) in the TP group, and 74.4% (0.63–0.82) in the PCR-negative group. If we included the participants with improved ulcers, the healing rates increased to 94.7%, 97.3% and 89.7% respectively. HD cases classified as not-healed all converted to HD-negative PCR.

Based upon clinical resolution and PCR conversion to HD-negative, a single oral dose of azithromycin is efficacious for the treatment of HD-CU. These results have implications for the treatment of individual patients and for the use of antibiotics in public health strategies to control CU in the tropics.