High Prevalence of Haemophilus ducreyi Among Patients With Suspected Primary syphilis in Malawi, 2019–2022

Abstract

Background As syphilis rates have increased globally, chancroid has dramatically declined as a cause of genital ulcer disease (GUD). Methods We recruited patients aged ≥18 years presenting to a sexually transmitted infection clinic with GUD from Lilongwe, Malawi, from November 2019 through April 2022. Lesion exudates were tested by darkfield microscopy (DFM) and polymerase chain reaction (PCR) for Treponema pallidum (TP) and by PCR for Haemophilus ducreyi (HD), herpes simplex virus, and Chlamydia trachomatis. We evaluated the sensitivity and specificity of DFM relative to TP PCR, the distribution of GUD etiologies by PCR, and the performance of our HD PCR relative to Allplex Genital Ulcer assay (Seegene Inc) using the Cohen's kappa statistic. Results We enrolled 568 participants; the median age was 27 years (interquartile range: 23, 34), 61% (345/564) were men, and 13% (60/464) had human immunodeficiency virus (HIV) or were newly diagnosed with HIV. DFM identified TP in 55 (10%) participants, with a sensitivity and specificity of 12% and 94%, respectively. PCR identified TP in 367 (65%), HD in 128 (23%), herpes simplex virus in 98 (17%), and Chlamydia trachomatis in 36 (6%) of participants with only 1/36 (2.8%) with serovar L1, L2, or L3 consistent with lymphogranuloma venereum; no etiology was identified in 48 (8%). External validation confirmed the high HD prevalence (Cohen's kappa 0.78, 89% agreement). Conclusions Syphilis and chancroid are common etiologies of GUD in Malawi. Our findings underscore the value of highly sensitive molecular diagnostic methods to periodically assess GUD causes among patients with sexually transmitted infections in countries using syndromic management.