A service provided by the BC Centre for Disease Control



Home / Resources / STI Updates (Blog) / New knowledge / What are the strongest risk factors for STIs?

What are the strongest risk factors for STIs?


Numerous research studies have explored the association between risk behaviors and infection with an STI. From a clinician’s perspective, the decision to recommend testing to a patient for a particular STI is usually informed by testing recommendations from public health organizations, such as the Public Health Agency of Canada (PHAC). However, from this multitude of research studies and testing recommendations, no clear guidance on the strongest STI risk factors has emerged.

This issue is particularly important when delivering STI services in an online environment, such as internet-based testing for STI and HIV, where there is limited access to STI clinicians. A better understanding of this issue can inform the ways in which individuals perceive risk and STI service programs recommend tests.

To begin to address this gap in knowledge, we reviewed the scientific evidence supporting risk factors commonly associated with chlamydia and gonorrhea infection, two of the most commonly diagnosed STIs.[1]

Summary of evidence

The findings of this evidence review revealed that the level of empirical support for known risk factors varied:

  • Age: Younger age was strong predictor of STI risk. There are a number of reasons why adolescents may be at greater risk for STIs than older people, including biological factors that make this group more vulnerable to chlamydia.
  • Socio-economic status (SES): SES was weakly associated with infection using any measure including educational level and employment status, which are regarded as unacceptable proxies for income.
  • Race/ethnicity: Race was moderately predictive of STIs, due to correlations between health care seeking patterns, poverty, insurance status, and race.
  • Sexual partnerships: Having multiple sexual partners was strongly associated with STIs.
  • Condom use: The evidence of the association between condom use and STIs was weak, likely due to the self-reported nature of condom use.
  • Drug/alcohol use: We found weak support for the association between drug/alcohol use and infection, probably due to the limited number of studies examining these risk factors.

Implications of findings

These findings should be viewed in light of some additional context.

First, it may be surprising that some behavioral risk factors, such as condom use and drug/alcohol use, were found to be weak predictors of STI. However, the under-reporting of “risky” behaviors is a long-standing issue in public health. On an individual level, consistent use of condoms limits the acquisition of STIs. In addition, the use of drug/alcohol in sexual relationships often leads to lower inhibition and decreased rates of condom use.

Second, additional research is needed to unravel how the scientific evidence associating race/ethnicity with STI outcomes can be more effectively understood. In particular, how that knowledge can be used to inform the scaling-up of screening interventions, without worsening existing sexual health inequalities, particularly among vulnerable sub-groups (e.g., people who are stigmatized and/or stereotyped by virtue of their ethnic identity).

Third, few high-quality studies specifically investigated the risk factors associated with infection among males. Testing women for STIs remains important from a public health perspective, but to do so while not adequately accounting for men within screening interventions could have unintended consequences (e.g., stigmatization of women’s bodies; reinforcing stereotypes about men’s ‘freedom’ from sexual health responsibilities).

Finally, there is a need to continue building the scientific evidence base to illuminate the mechanisms and pathways of STI acquisition in order to inform how intervention practices unfold in the future, including internet-based testing initiatives.


  1. Falasinnu, T; Gilbert, M; Salway, TH; Gustafson, P; Ogilvie, G; Shoveller, J. Predictors identifying those at increased risk for STDs: a theory-guided review of empirical literature and clinical guidelines. Int. J. STD AIDS. 2014 Oct 16. pii: 0956462414555930.


The author would like to thank her other co-authors: Mark Gilbert, Paul Gustafson, Gina Ogilvie, Jeannie Shoveller, and Travis Hottes Salway. Funding for this research was provided by the Canadian Institute of Health Research.