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Syphilis, which is caused by the sexually transmitted bacterium Treponema pallidum subsp. pallidum, has an estimated 6.3 million cases worldwide per annum. In the past ten years, the incidence of syphilis has increased by more than 150% in some high-income countries, but the evolution and epidemiology of the epidemic are poorly understood. To characterize the global population structure of T. pallidum, we assembled a geographically and temporally diverse collection of 726 genomes from 626 clinical and 100 laboratory samples collected in 23 countries. We applied phylogenetic analyses and clustering, and found that the global syphilis population comprises just two deeply branching lineages, Nichols and SS14. Both lineages are currently circulating in 12 of the 23 countries sampled. We subdivided T. p.pallidum into 17 distinct sublineages to provide further phylodynamic resolution. Importantly, two Nichols sublineages have expanded clonally across 9 countries contemporaneously with SS14. Moreover, pairwise genome analyses revealed examples of isolates collected within the last 20 years from 14 different countries that had genetically identical core genomes, which might indicate frequent exchange through international transmission. It is striking that most samples collected before 1983 are phylogenetically distinct from more recently isolated sublineages. Using Bayesian temporal analysis, we detected a population bottleneck occurring during the late 1990s, followed by rapid population expansion in the 2000s that was driven by the dominant T. pallidum sublineages circulating today. This expansion may be linked to changing epidemiology, immune evasion or fitness under antimicrobial selection pressure, since many of the contemporary syphilis lineages we have characterized are resistant to macrolides.

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ObjectivesYoung people are a critical target group for sexually transmitted infections (STI) surveillance due to their particular behavioural and social related vulnerability. The aim of this study was to describe the epidemiological characteristics and trends in the incidence of gonorrhoea, syphilis, HIV and venereal lymphogranuloma (LGV) among 15–24-year-olds in Barcelona, and to determine factors associated with HIV coinfection.DesignWe performed a population-based incidence study covering the 2007–2015 period.ParticipantsAll new cases of STI—HIV, gonorrhoea, infectious syphilis and LGV—notified to the epidemiological surveillance system in Barcelona between 2007 and 2015. 1218 cases were studied: 84.6% were men, 19.3% were 15–19 years old and 50.6% were born in Spain. Among men, 73.7% were men who have sex with men (MSM); among women, 85.6% were women that have sex with men.Primary and secondary outcomesIncidence of HIV, gonorrhoea, infectious syphilis and LGV. HIV coinfection.ResultsThere was an increase in the incidence of gonorrhoea, from 1.9 cases per 10 000 people in 2007 to 7.6/10 000 in 2015 (p<0.01), in MSM from 27.1 to 228.8/10 000 (p<0.01). The incidence of syphilis increased from 0.4/10 000 in 2007 to 3.1/10 000 in 2015 (significant in men only, p<0.01), in MSM from 18.1 to 116.9/10 000 (p<0.01). The incidence of HIV showed a non-significant increase in men (p=0.27), and that of LGV remained stable (p=0.59). Factors associated with increased risk of HIV coinfection included being MSM (adjusted OR[ORa]=14.14, 95% CI 3.34 to 59.91) and having >10 sexual partners (ORa=4.11, 95% CI 1.53 to 11.01) or STI diagnosis during the previous 12 months (ORa=2.06; 95% CI 1.13 to 3.77).ConclusionsThe incidence of gonorrhoea and syphilis among 15–24-year-olds increased, while HIV infection remained stable but with a high incidence among MSM. Being MSM, having sex with multiple partners and having a diagnosis of an STI in the previous 12 months were factors associated with HIV coinfection.

Human intestinal spirochetosis (HIS) is a possible cause of chronic diarrhoea and affects mainly men who have sex with men (MSM) and people living with HIV. Diagnosis is based on colon biopsy, where spirochetes can be observed on the luminal surface, especially with the Warthin-Starry stain or similar silver stains. We conducted a retrospective descriptive study of all HIS cases diagnosed in two sexually transmitted infections (STI) centres in Barcelona from 2009 until 2018. The medical histories were reviewed to gather epidemiological, clinical, and diagnostic variables. Six patients were diagnosed with HIS. All the individuals were MSM, with a median age of 31.5 years (interquartile range [IQR] 29.5;49.25) and half of them were living with HIV. Five patients reported condomless anal intercourse and 4 patients had practised oro-anal sex previously. Concomitantly, two of them had rectal gonorrhoea, one had rectal Chlamydia trachomatis and none of them had syphilis. The predominant clinical symptom was diarrhoea (5 patients). All cases were diagnosed by a Warthin-Starry stain on a colon biopsy specimen, and mild inflammatory changes were found in 5 cases. Five patients were treated with metronidazole and one with benzathine penicillin G. Treatment was successful in all the patients. HIS should be considered in patients with chronic diarrhoea who report risky sexual practices and/or concomitant STI. HIS may also be sexually transmitted according to the context.