Sexually transmitted infections—Research priorities for new challenges

The World Health Organization (WHO) estimates that more than 1 million new sexually transmitted infections (STIs) are acquired each day [1].STIs are pernicious players in the global burden of disease, their management stymied by the diversity of pathogens, social stigma, and commonly mild or nonexistent symptoms.As quietly as they persist, STIs have prominent sequelae-for example, roughly one-third of pregnant women infected with syphilis experience adverse birth outcomes including stillbirth, human papillomavirus (HPV) infection leads to an estimated 266,000 cervical cancer deaths annually, and some bacterial STIs cause pelvic inflammatory disease, female infertility, preterm delivery, and low birthweight.The imperative for innovation at this time is one of the strategic directions of the WHO global health sector strategy to address the burden of STIs [2].This month, PLOS Medicine launches the research content from our Collection on Prevention, Diagnosis, and Treatment of STIs.The Collection will feature Research Articles submitted in response to our call for papers this past summer, with related Perspectives from international STI experts.Two pressing themes frame current research in this area.First, the means of prevention for HIV and for other STIs are now decoupled, with gonorrhoea and syphilis amongst men who have sex with men on the rise as an unintended consequence of antiretroviral therapy that renders HIV undetectable in blood, and of the availability of pre-exposure prophylaxis (PrEP) [3].When condoms were the main prevention technology for all sexually transmitted pathogens, prevention messages were unified but uptake was patchy.PrEP, on the other hand, is now being adopted and adhered to more readily by the people at highest risk of acquiring HIV infection, but does not prevent any other STI.In anticipation of increases in risky sexual behaviours in the context of PrEP, researchers and practitioners should actively promote primary STI prevention, including promotion of barrier methods.Indeed, secondary prevention strategies, including more frequent screening for STIs, are not a panacea because an increased rate of untargeted treatment can drive antimicrobial resistance (AMR) [4].Second, modern STI management is being increasingly challenged by AMR, which has already compromised the treatment of gonorrhoea [5] and is expanding geographically.Some possible solutions to the threat of AMR are explored in the Collection.In their mathematical modelling study, Xavier Didelot and colleagues project how cautious use of previously abandoned antimicrobials could mitigate the spread of resistance [6].A linked Perspective by Magnus Unemo and Christian Althaus discusses the study in the context of current knowledge about gonococcal resistance to cephalosporins [7].Additionally, risk assessment of the impact on AMR should likely be required before the introduction of new preventive strategies or guidelines.For example, new molecular diagnostic tests for Mycoplasma genitalium, which is under-recognised as a cause of urethritis and cervicitis, are considered likely to worsen already