Article Text

Original article
Self-perceived risk and prevalent chlamydia infection among adolescents in Norway: a population-based cross-sectional study
  1. Kirsten Gravningen1,
  2. Tonje Braaten2,
  3. Henrik Schirmer3,4
  1. 1Department of Microbiology and Infection Control, University Hospital of North Norway (UNN), Tromsø, Norway
  2. 2Department of Community Medicine, Faculty of Health Sciences, The Arctic University of Norway, Tromsø, Norway
  3. 3Institute of Clinical Medicine, The Arctic University of Norway, Tromsø, Norway
  4. 4Department of Cardiology, Division of Cardiothoracic and Respiratory Medicine, Tromsø, Norway
  1. Correspondence to Kirsten Gravningen, Department of Microbiology and Infection Control, University Hospital of North Norway (UNN), Tromsø, Norway; kirsten.gravningen{at}


Objectives Risk judgements are key factors in adolescents’ decisions related to sexual health. We examine the associations between self-perceived risk and prevalent chlamydia infection, and sexual behaviours related to risk perception in a general adolescent population in Norway.

Methods Population-based cross-sectional study among 1028 sexually experienced girls and boys, age 15–20 years (85% participation), including web questionnaires and urine samples for Chlamydia trachomatis PCR testing. Participants rated self-perceived risk as: no/low/medium/high/very high. We used binary and ordinal logistic regressions to examine associations with chlamydia prevalence and self-perceived risk, respectively, adjusting for potentially confounding variables.

Results Chlamydia prevalence increased with increasing risk perception. Although girls had twice the chlamydia prevalence of boys (7.3% vs 3.9%), their risk distribution was similar and 65% of both genders rated their risk as no/low with half of infections detected in this group. In multivariable analyses, reporting multiple sexual risk behaviours, non-steady relationship, previous chlamydia testing and treatment, and urogenital symptoms increased self-perceived risk. More boys overestimated their personal risk whereas more girls underestimated it (52% vs 30%, respectively, and 15% vs 31%, p<0.001). The main reasons for perceiving no/low risk were: ‘I have a steady partner’ and ‘I trust my partner will tell me about an infection’.

Conclusions These sexually experienced adolescents acknowledged their chlamydia infection risk, but wrong beliefs were incorporated in their assessments, and more than half had incorrect risk perception. We suggest that sexually transmitted infection prevention programmes should be directed at closing the gap between perceived and actual risk and focus on how context may bias personal judgement.


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Judgments about risk are assumed to be key factors in young peoples’ decisions concerning behaviours related to sexual health and have been included in sexually transmitted infection (STI) intervention programmes and educational campaigns.1–3 The risk of acquiring an STI depends on the sexual behaviour of the individual and his or her sexual partners, and the infection prevalence in the mixing population. Three-quarters of all genital Chlamydia trachomatis infections in Europe are detected in the age group 15–24 years with Norway having the third highest rate of notified chlamydia cases.4

Adolescents’ self-perceived risk of C. trachomatis infection may be influenced by its mostly asymptomatic course,5 limited personal experience of STIs, wrong beliefs due to lack of specific knowledge,6 and by the influence of alcohol and drugs while making sexual decisions.7 Subjective invulnerability and an optimistic bias related to one's own sexual health may alter personal risk perception.2 ,8–10 Adolescents may use stereotypical beliefs based on appearance and inferred personal characteristics when they assess STI-risk in a sexual partner.11 Qualitative studies reveal that sexual partners who are known and considered similar to oneself are more likely to be perceived as safe and consequently adolescents may not view their partner as a possible source of STIs.11 Intimacy and romantic feelings may further influence their perception of STI risk.12

In Norway, mandatory school-based sexual health education is provided for five school years starting at age 11 years.13 Widespread public youth clinics with open access offer free and confidential STI services including partner notification. The Norwegian guidelines recommend chlamydia testing in presence of clinical symptoms, if partner is infected, or in persons <25 years after change of sexual partner.14 Frequent public health campaigns are launched to increase awareness of STI risk and promote safe sex. The national health authorities distribute free condoms to persons younger than 25 years as consistent and proper condom use provides the best protection against transmission of bacterial and viral STIs.3 ,15 ,16 Despite this, young Norwegians remain poor condom users.17 ,18 Prevention of unwanted pregnancies is frequently the predominant concern and may provide stronger motivation for contraceptive use than STI protection.11 ,18

We measured self-perceived chlamydia risk in a cross-sectional study in Finnmark county, Norway, in 2009 inviting all classes in 5 of 10 public high schools.17 Chlamydia prevalence was found to be 7.3% among the sexually experienced girls and 3.9% among the boys.17 Our objectives are to: (1) examine whether level of self-perceived risk is associated with chlamydia infection prevalence among adolescents in Norway, (2) the demographic and sexual behaviour characteristics associated with risk perception, and (3) the reasons for perceiving no or low chlamydia infection risk.


A detailed description of study design and data collection has been reported elsewhere.17 Public high schools in Norway enrol 94% of birth cohorts, include academic programmes and vocational school, and so are assumed to be representative for the general adolescent population. Researchers visited 123 classes in the five schools, inviting students to complete a web questionnaire on demography, alcohol use, self-perceived risk of prevalent chlamydia infection, sexual behaviour, urogenital symptoms and chlamydia infection history, and to provide first-void urine samples. Researchers and the class teacher were present while participants spent 10–20 min answering the questionnaire on their laptops. Directly thereafter, participants provided 12 mL first-void urine which was delivered to the laboratory on the following day for C. trachomatis PCR testing (ProCelo as, Tromsø, Norway). Participants testing positive were called on their mobile phone within 2 days and given an appointment at the local youth clinic for treatment with azithromycin 1 g, partner notification and follow-up.

The response rate was 85% (1618 of 1908) of all eligible (see online supplementary file 1).17 Four hundred and forty-two participants reporting no sexual intercourse (all of whom had negative chlamydia test results) were considered not to be at risk for chlamydia and were excluded from the current analysis. A total of 1028 participants (564 girls and 464 boys) with sexual intercourse experience, valid chlamydia test results and valid response to the questions on self-perceived risk were included in the analysis. Median age was 17.0 years (range 15–20 years).

Data from questionnaire

Self-perceived risk for prevalent chlamydia infection was indicated with the question; ‘How do you perceive your current risk of being infected with chlamydia?’ and rated as: 1=no risk, 2=low, 3=medium, 4=high, 5=very high and 6=don't know. Participants who perceived no or low risk were asked to give the reason(s) for this by choosing one or more of six predefined statements.

Alcohol use was reported as: never tried, tried, occasional use and regular use. Due to small numbers, the categories never tried and tried were merged.

Early first intercourse was defined as sexual debut before age 15 years in agreement with a recent study assessing sexual risk-taking behaviour among Nordic women.19

Relationship with the most recent sexual partner was categorised as (1) steady, (2) ex-partner, (3) a friend I have sex with and (4) casual. In ordinal logistic regression analysis the relationship variable was dichotomised as ‘steady’ (=1) versus ‘non-steady’ (=2–4) sexual partner.

Condom use (yes/no) was reported for first sexual intercourse with the most recent sexual partner as use at this occasion is assumed to be a valid representation of condom use with former new partners.20

Statistical analyses

We used STATA (V.13.0) for all statistical analyses. Using the exact binominal method, 95% CIs for proportions were calculated. Logistic regression was used to calculate ORs to assess associations between self-perceived risk and prevalent chlamydia infection. To investigate factors associated with risk perception, crude and multivariable ordinal logistic regression analyses were used with the dependent variable ‘self-perceived risk’ in four categories: no, low, medium and high/very high, while ‘don't know’ was coded as missing. The ordinal logistic regression model estimates one regression coefficient over the four levels of self-perceived risk and calculates the probability of being in the higher categories of the dependent variable. Selection of explanatory variables was based on current literature19 ,21 ,22 and factors we believed a priori to be important.17 All variables were retained in the multivariable models and tested for gender-interaction. Correlations between variables were assessed using Spearman's rank-order correlation analyses. Collinearity was assessed as low with variance inflation factor <1.62 for all variables.23 Equal distance between adjacent risk levels was tested using Wald and Brant tests of parallel lines with all variables meeting the proportional odds assumption except for the variable ‘previous chlamydia testing’ which was excluded. Model fit was assessed using Pulstenis and Robinsons modified Pearson's χ2 test indicating good model fit.24 Estimated risk of prevalent chlamydia infection was calculated using logistic regression analysis (by gender) with inclusion of the same a priori risk factors as used in the model for self-perceived risk of chlamydia. For each gender estimated risk was divided in four levels based on quartile values. We generated a new variable ‘risk difference’ based on the difference between estimated risk and self-perceived risk where: risk difference=0 corresponds to no difference between the two, risk difference <0 corresponds to self-perceived risk being higher than estimated, and risk difference >0 corresponds to estimated risk being higher than self-perceived.


Written informed parental consent was obtained for participants <16 years. Participants >16 years gave their informed consent by filling in the web-based questionnaire.


A detailed description of this sexually experienced adolescent population has been reported previously.17 In brief, more girls than boys reported: early sexual debut, same-sex sexual experiences, having steady partners, older most recent sexual partner, and having been tested and treated for chlamydia infection before the study took place. The boys more commonly reported: alcohol use, casual sexual partners, same-age or younger partners, and having used condom at first sex with the most recent partner.

Risk perception and chlamydia infection prevalence

Girls and boys had similar distribution of chlamydia risk perception with 65% (n=665) stating none or low risk, 23% medium risk, 6% high or very high risk, and 6% did not know (table 1).

Table 1

Chlamydia infection prevalence and crude OR of infection stratified by self-perceived risk level

Half the chlamydia infections were detected in the no/low risk group despite low prevalence among both genders. The increase in chlamydia prevalence with higher risk perception was statistically significant in girls only and, when merging the ‘no/low’ and ‘medium/high/very high’ risk groups, also among boys (p=0.019).

Among the participants responding ‘don't know’, 62 of 63 provided a urine sample in our screening with no infections detected. Girls who were previously treated for chlamydia had a prevalence of 9.8% (11 infections in 112 girls) and boys had 6.3% (2 infections in 32 boys).

Factors associated with self-perceived risk

Self-perceived risk of chlamydia infection was in crude analysis associated with multiple sexual risk behaviours and also alcohol use, prior chlamydia treatment and urogenital symptoms (table 2).

Table 2

Factors associated with level of self-perceived risk of chlamydia infection in ordinal logistic regression analysis, by gender

In the multivariable model for girls, the strong effect of reporting multiple recent sexual partners was significantly reduced (OR: 8.35, adjusted OR, AOR: 5.10) as was reporting most recent sex with a non-steady partner (OR: 3.24, AOR: 2.08). The two had a moderate positive correlation (r=0.39) and by excluding one, effect size of the other significantly increased. Furthermore, among girls, crude effect sizes were attenuated by more than 10% for reporting: same-sex/bisexual sexual orientation, alcohol use, early first intercourse (before age 15 years), older most recent sexual partner, no condom use at first sex with this partner, substance use related to last sex, prior chlamydia treatment and urogenital symptoms, indicating evidence of confounding. The effect size of vocational school increased by 50% among girls, but exclusion of vocational school from the model did not significantly alter the other adjusted estimates. A similar trend was observed among the boys with crude regression estimates of alcohol use, sexual behaviours, prior chlamydia treatment and urogenital symptoms being attenuated by more than 10%, also indicating evidence of confounding. Among boys, the strong effect size of condom use at first sex with the most recent partner (OR: 1.99) was strongly attenuated by inclusion of the sexual behaviour variables all contributing to this attenuation (AOR 1.14). Statistically significant differences between the gender's multivariable models were observed for urogenital symptoms only.

Participants who rated their risk as medium or high/very high were more likely to have been tested for chlamydia infection previously than those perceiving no/low risk (figure 1). Girls and boys previously treated for chlamydia infection reported less condom use than those reporting no treatment (girls: 14.4% vs 36.7%, boys: 16.1% vs 46.7%, both p<0.001, respectively) and they more often reported two or more sexual partners in the past 6 months (girls: 62.2% vs 37.1%, boys: 67.7% vs 39.3%, both p<0.001, respectively).

Figure 1

Prevalence of previous chlamydia testing among girls and boys stratified by self-perceived risk level including 95% CIs.

Difference between self-perceived and estimated risk

Compared with estimated risk of chlamydia infection derived from a model using the same known risk factors as above, more boys overestimated their personal risk whereas more girls underestimated it (52% vs 30%, respectively, and 15% vs 31%, p<0.001) (see online supplementary file 2).

No or low perception of risk

In the subgroup of 359 girls and 306 boys perceiving no/low risk, those with infection and a significant proportion of the non-infected, reported multiple known risk factors (see online supplementary file 3). The two main reasons cited for no/low risk perception were: ‘I have a steady partner’ and, as reported by half of participants, ‘I trust my partner will tell me if he/she is infected’ (table 3).

Table 3

Reasons for reporting no/low infection risk, corresponding chlamydia infection prevalence and OR for prevalent infection, among 665 sexually experienced participants

A total of 77% girls and 50% boys in the no/low risk group reported last sex with a steady partner, and among these, more boys than girls trusted their partner to tell them about a chlamydia infection (59% vs 40%, p<0.001). Only 11% of girls and 27% of boys perceived no/low risk due to consistent condom use (table 3). More boys than girls claimed ability to assess whether the partner was infected in advance (13% vs 5%).

Chlamydia infection prevalence was 5.6% in girls and 2.6% in boys in the no/low risk group. Chlamydia prevalence among those reporting having a steady partner as reason for perceiving no/low risk was 5.5% among girls and 1.8% among boys (13 vs 2 chlamydia infection cases, respectively). Girls trusting their partner to tell about chlamydia infection had prevalence 8.3% and boys had 3.2% (14 vs 4 cases). Girls in the no/low risk group reporting consistent condom use had chlamydia prevalence 7.3% (3 cases) while the condom-using boys had no infections. A minority of the sexually-experienced girls and boys (0.8% and 3.9%) in the no/low risk group said: ‘I have not had sex for more than 3 months’ and no infections were detected among them.


Self-perceived risk among these sexually experienced adolescents was associated with chlamydia infection prevalence and with well known chlamydia risk factors, but also with wrong beliefs which may explain why more than half the participants either overestimated or underestimated their personal risk. More boys than girls overestimated their risk, and more girls underestimated their risk, resulting in equal risk perception among genders although chlamydia infection prevalence among girls was twice that of boys.

Our participants had high chlamydia infection prevalence in comparison to other studies.17 In line with other research, the majority of the participants perceived themselves to be at low risk of chlamydia infection despite a substantial proportion engaging in behaviours that clearly place them at risk.21 ,22 ,25–27 Although more boys than girls reported condom use at first sex with the most recent partner, condom use at this occasion remained significant only in the girls’ final model for risk perception. The fact that only a minority in the no/low risk group justified their risk assessment with consistent condom use was disconcerting considering the easy availability of condoms in Norway and the public awareness of their efficacy in STI prevention. Girls reporting no/low risk and claiming ‘I always use condom’ as reason for this had the same chlamydia prevalence (7.3%) as the female average possibly due to condom use errors or recall bias.27

In line with two recent population-based studies, we found higher numbers of sexual partners to be a strong predictor of increased risk perception in both genders.21 ,28 The association between relationship status and risk perception is a common finding and probably based on assumptions of the monogamous and committed nature of steady relationships.21 ,26 ,27 The finding that girls citing steady partner as reason for no/low risk perception had threefold higher chlamydia prevalence than the corresponding boys (5.5% vs 1.8%) may be due to the girls mostly having older partners linking them to sexual networks with higher chlamydia prevalence.17

Although participants with higher risk perception were more likely to have been chlamydia tested prior to our study, a considerable proportion were not tested as also shown by others.26 As expected, personal experience with chlamydia infection increased risk perception and might provide a powerful stimulus to preventive action.2 However, participants previously treated for chlamydia reporting higher levels of risky sexual behaviour than those never treated suggests failure to integrate risk perception into their personal interactions, lack of self-efficacy to adopt preventive measures, or unwillingness to change.1 Alternatively, adolescents may not see chlamydia infection as severe enough to change their behaviour due to lack of symptoms, the easy and efficient cure, and threats of long-term complications related to female reproductive morbidity perceived irrelevant in the current phase of life.29

The finding that half in the no/low risk group trusted their partners to tell about a chlamydia infection suggests unrealistic expectations of testing frequency and willingness to share the test results among partners. Only a minor proportion of the no/low risk group believed they could assess an infected partner in advance suggesting that external characteristics were not commonly used risk indicators among Norwegian adolescents in contrast to the participants in a US study.11

Strengths and limitations

This is one of few studies on self-perceived chlamydia infection risk in an adolescent general population that includes both genders and the use of chlamydia testing in biological samples. The high participation is a strength of our study and the finding of positive chlamydia test results only among the sexually experienced suggests truthful reporting. Limitations include the cross-sectional design so it is not possible to establish temporality or infer causality and limited statistical power due to few chlamydia cases in particular among boys. Although the use of a web questionnaire to assess sensitive behaviours is likely to have reduced social desirability bias, our data could still be prone to such bias.30 Risk markers such as sexual concurrencies, perceptions of partners’ risk, and sexual practices such as anal sex should have been included.31 Finally, our results may be applicable mainly to the Nordic countries.

Implications for policy and further research

Although self-perceived chlamydia risk was associated with a range of sexual risk behaviours among these potentially well informed sexually experienced adolescents, wrong beliefs and subjective perceptions were common and may have interfered with practices within their personal relationships. Our data show the need for examining real knowledge of sexual health and STI risk among adolescents in Norway and how this influences risk perception and further translates into safe-sex behaviour with their partner(s). Future population-based studies should include national probability sampling to be more representative, larger sample size, and detailed questions on sexual health knowledge, characteristics of several recent relationships, and perceptions of partner risk with the aim to inform sexual health education at school and STI prevention programmes.


These sexually experienced adolescents acknowledged their chlamydia infection risk, but more than half had incorrect risk perception. Our findings call for an evaluation of the STI control strategies towards adolescents in Norway. We suggest that interventions directed at closing the gap between perceived STI risk and actual risk should focus on how context, for example having a steady partner, may bias self-perceived risk thereby preventing safe-sex knowledge from being applied to personal sexual encounters.

Key messages

  • Among these sexually experienced adolescents in Norway, chlamydia infection prevalence increased with increasing risk perception suggesting acknowledgement of personal risk.

  • Although girls had twice the chlamydia prevalence of boys, they reported similar distribution of self-perceived risk, with more boys than girls overestimating their risk.

  • A majority of both genders perceived themselves to be at no/low risk of chlamydia infection despite engaging in sexual behaviours that clearly placed them at risk.

  • Wrong beliefs were incorporated into both genders’ risk assessments and we suggest sexually transmitted infection prevention programmes should focus on how context and relationship status may bias risk judgement.


The authors thank the study participants, the study nurse Randi Olsen who assisted in data collection, and Soazig Clifton for help with formatting and language.


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Supplementary materials

  • Supplementary Data

    This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.


  • Handling editor Jackie A Cassell

  • Contributors KG conceived and designed the study, collected the data and drafted the manuscript. KG and TB performed the statistical analyses. All authors contributed to the interpretation of the results, and revised and approved the manuscript.

  • Funding Data collection was funded by The Norwegian Directorate of Health (grant number 2009001019) and SpareBank 1 Nord-Norges Medical Research Grant (SNN 20080529). The funding bodies had no interest in design, collection, analysis, and interpretation of data, or manuscript writing.

  • Competing interests None declared.

  • Ethics approval The Regional Committee for Medical and Health Research Ethics North Norway. The ethics approval number for this study was provided by the REC North Office (Regional Committees for Medical and Health Research Ethics): P REC North 23/2009.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement The data were collected for the PhD of principal investigator KG. The data are stored in a research database at the University Hospital of North Norway and are still being explored. From September 2015, data can be accessed by others after application.

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