Detection of Treponema pallidum in injured and uninjured sites in men who have sex with men with early syphilis: a prospective and cross-sectional study

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Background

The transmission of syphilis is increasing, and precisely how Treponema pallidum is sexually transmitted from person to person is unclear. We sought to determine the frequency of T pallidum shedding from potentially asymptomatic sites and the stage of infection at which shedding is most common in men who have sex with men (MSM), who have been disproportionately affected by syphilis.

Methods

We carried out a prospective and cross-sectional study among MSM recruited from the Melbourne Sexual Health Center (Melbourne, VIC, Australia). Men were eligible if they were 18 years of age or older, had reported sex with men in the past 12 months, and had laboratory-confirmed primary, secondary or early latent syphilis, according to Australian definitions. Primary and secondary syphilis lesions were taken on a swab and uninjured samples were taken by mouth rinse, oral cavity swab, anal canal swab, urine and semen. Samples were tested for T pallidum using PCR tests targeting polA (injured and uninjured samples) and 47 kDa target genes (uninjured samples only). The primary outcome measure was the proportion of men with T pallidum detected from potentially asymptomatic sites, namely the mouth, anus, urethra and semen.

Results

Between November 30, 2015 and May 23, 2019, 246 MSM were screened for inclusion, 200 of whom had serologically confirmed early syphilis and were included in the study: 54 (27%) out of 200 had primary syphilis, 93 (47%) had secondary syphilis and 53 (27%) had early latent syphilis. T pallidum DNA was detected in 48 (24%; 95% CI 18 3–30 5) of 200 men by mouthwash or oral lesion swab, or both, of whom 24 had no oral lesions . Oral T pallidum detection was more common in people with secondary syphilis compared to those in other stages of the disease (41 [44%] out of 93 vs Seven [7%] of 107; p vs 11 [13%] of 83; p = 0.0026). T pallidum was detected by anal canal swab or anal lesion swab, or both, in 45 (23.0%; 95% CI 17.3–29.5) of 196 men with available samples, ten of whom did not had no anal injury. Otherwise,
T pallidum was detected in urine samples from 12 (6 · 1%, 3 · 2–10 · 3) from 198 men and in semen samples from six (12 · 0%, 4 · 5–24 · 3) of the 50 men who provided samples. Of the 93 men with secondary syphilis, 69 (74%) had T pallidum detected at any site, and 24 (26%) were detected at two or more separate sites. Of the 54 men with primary syphilis, 49 (91%) had T pallidum detected at any site, and 11 (20%) were detected at two or more separate sites. Of the 53 men with early latent syphilis, four (8%) had T pallidum detected on any site and none had T pallidum detected at two or more separate sites.

Interpretation

Unrecognized oral and anal excretion of T pallidum occurs in MSM with early syphilis, most often in those with secondary syphilis, suggesting that secondary syphilis is the most infectious stage and that earlier detection and treatment of syphilis to prevent progression to the secondary stage could improve the control of syphilis. Future research is needed to determine the contribution of excretion T pallidum sites not damaged by the transmission of syphilis.

Funding

Australian National Council for Health and Medical Research.



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