In a recent article in this journal, Dr Hunter Handsfield1 rekindled a long-standing debate: what, if any, is the difference between sexually transmitted infection (STI) and sexually transmitted disease (STD)? Although there may be more critical issues in our field to lose sleep over, the STI/STD debate is not quite trivial. The question comes up often enough in our trainings, and most of our students think that there is indeed a difference, although they may not know what it is. Thus, arguments from an undisputed leader in the field like Dr Handsfield, suggesting that we should not fret too much about the difference between “infection” and “disease” and that STI and STD may and probably will be used interchangeably for times to come, seem to put this issue to rest.
However, before we do, here are a few thoughts that might inform and perhaps prolong the discourse a bit.
The distinction between infection and disease has served us well in public health and STD/HIV prevention practice. Traditionally, we recognize 3 levels of prevention. In the context of STI/STD, primary prevention aims to block the acquisition of the pathogen, that is, prevents infection; secondary prevention aims to impede the progression from infection to disease, and tertiary prevention reduces long-term complications. This differentiation translates in distinct prevention efforts, including behavioral interventions for primary prevention, identification and treatment of asymptomatic infections in secondary prevention, and treatment of symptomatic infections and their sequelae in tertiary prevention. Thus, from a public health perspective, the distinction between STI and STD should be clear and relevant.
Of course, for many decades, the diagnosis and treatment of gonorrhea, chlamydia, and syphilis have been the cornerstone of STI prevention, effectively using secondary and tertiary prevention for the index case as primary prevention of onward transmission to sex partners and thus blurring the difference.
In HIV prevention, however, the realms of primary and secondary/tertiary prevention have been clearly separated for many years; public health programs were responsible for the prevention of infection and medical care providers for the prevention and treatment of disease. Interestingly, the focus on HIV primary prevention in the 1980s and 1990s had spillover effects in STI/STD prevention, resulting in a greater focus on behavioral interventions for primary prevention. This “upstream” thinking may have well facilitated the introduction of the term “sexually transmitted infections” in our public health parlance during this time period.
Recently, we have come to appreciate that treatment of HIV infection is an effective tool in the prevention of HIV transmission. Thus, “treatment as prevention,” long the leading paradigm in STD control, has now entered the world of HIV prevention. This has considerable consequences, not in the least for HIV care providers who are now not only advocating for their patients but also for their uninfected sex partners, effectively adding a public health role to their traditional provider role. Conversely, public health HIV programs are now much more invested in HIV testing and linkage to care and pivoting away from a strict primary prevention paradigm.
As primary and secondary prevention interventions are merging in a single prevention approach, the distinction between “infection” and “disease” becomes less relevant from a public health perspective. These developments are not without consequences. In my view, leaving the primary prevention paradigm has coincided with increases in high-risk behaviors, particularly among men who have sex with men and associated STI/STD epidemics, including lymphogranuloma venereum and syphilis and perhaps now also sexually transmitted hepatitis C. The further medicalization of HIV prevention through preexposure and postexposure prophylaxis may further compound these negative side effects.
So, the public health part of my professional persona would like to hold on to the “STI” terminology as it implies a more holistic and more upstream prevention approach. That said, my medical counterpart suggests that we only care about STIs insofar as they result in significant disease: gonorrhea and chlamydia because they are major factors in causing infertility and ectopic pregnancy among women, syphilis because of its long-term consequences if left untreated and the potential of severe morbidity and mortality when vertically transmitted, and human papillomavirus because of its linkage to cervical and other anogenital cancers. Conversely, we do not seem to care much about ureaplasmas that appear to cause a lot of infection, but little disease.
Putting the parts together, I agree with Dr Handsfield that we can use both STI and STD, but perhaps not interchangeably. Wearing my public health hat, I like to think in terms of STI prevention and sexual health promotion. But on the days that I don my laboratory coat, I see patients with STDs in the STD clinic.
Finally, should we discontinue STI and STD and endorse a different moniker altogether? In his article, Dr Handsfield suggests that not all STDs are necessarily infections and that “disorder” might be a better term. Maybe. In that context, however, I think it is informative to see how STDs are referred to in other languages. Spanish speakers say “enfermedades de transmisión sexual,” the French say “maladies sexuallement transmissibles,” and the Germans “Sexuell übertragbare Erkrankungen.” Rather than defining conditions by what they are not (as in “dis-ease” and “dis-order”), our colleagues abroad identify them more directly as “sickness” or “illness.”
Hmmm… sexually transmitted illness—“STI”—now there is a concept!
1. Handsfield HH. Sexually transmitted diseases, infections, and disorders: What's in a name? Sex Transm Dis 2015; 42: 169.