This study is the only population based study measuring chlamydia and associated factors in young Norwegian men and women in one county where the study sample is drawn from the national population register, which includes the entire population, and not from a selected group of individuals. It is also among the rare prevalence studies were home sampling by postal recruitment was used. We found a chlamydia prevalence of 5.5% in our population. The likelihood of infection increased with a greater number of partners. Among women, those with a previous chlamydia diagnosis (and those who had not previously consulted their family doctor on STIs) were more likely to have a current infection. Among men the odds of infection increased by 8.6 times if they believed there was no local youth clinic present. The majority did not use condom at last sexual intercourse with a casual partner.
Prevalence of chlamydia, and other self reported STIs
We measured a chlamydia prevalence of 5.5%. Other chlamydia prevalence surveys in Norway have found from 1 to 9% depending on the basis of their population.[7
]. A study among all high school graduates (18
year olds) in one Norwegian municipality found a chlamydia prevalence of 2% among those who had had their sexual debut [9
]. Another prevalence study among Norwegian male students aged 18–30 recruited at student campus and students health centres measured a chlamydia prevalence of 7.8% [10
]. A home based chlamydia prevalence survey among patients 18–29 of age listed at a general practice in Oslo gave a chlamydia prevalence of 3% [7
]. A chlamydia prevalence of 9% was found among young girls 16–19
years seeking youth clinic for hormonal prevention [14
] and 6% among women (16–24) seeking abortion [15
]. Our results are in the mid-range of what is found in other publications from Norway, lower than in the populations seeking health care, but higher than most other studies conducted in different populations outside the health care system. Population based studies offering home sampling for chlamydia outside Norway has shown a prevalence ranging from 1 to 7%[16
Seven percent reported a history of genital warts in our sample. This is lower than reported from other Nordic countries.[21
Sexual behaviour and health care use
According to the national sexual behaviour studies in Norway the age for sexual debut has been decreasing from 1987 to 2002 when the median age was 17,5
years for men and 17.1
years for women [22
]. Another publication on decreasing trends for age for sexual debut among Norwegian youth from the same time-period reported median age for sexual debut to 18.0
years for men and 16.7
years for women in 2002 [23
] In the study among male students the median age for sexual debut was 17.5[10
]. A recent publication on sexual behaviour among Nordic women reported a median age of 16
years for the first intercourse for the Norwegian women involved [24
]. Our results do not differ much from these other studies. We found a slightly lower mean age for sexual debut among the men in our study. This could be the result of a continuous decreasing trend. However, it could also indicate that men with an earlier sexual debut or who felt more at risk of infection were more likely to take part in our study. Only 17% reported using condom at last sexual intercourse with casual partner. This result is supported by the National sexual behaviour studies[22
]. In the study among male students 76% reported not using condom at last intercourse[10
], The condom use among young Norwegians is however less frequent than reported from other European countries [25
Factors associated with infection
A greater number of partners is well documented as a risk factor for chlamydia[26
]. Condom use[26
] and presence of genital symptoms[30
] have by many been documented as risk factors, but this is not universal. We also found that having multiple partners was associated with a positive test result, but condom use at last sexual intercourse with non- steady partner and presence of genital symptoms (discharge, endocervical bleeding, pelvic pain, urethral itching, dysuria) was not associated with infection, neither was any of the socio-demographic factors measured in this study (age, marital status, education, occupation, country of birth).
Among men, reporting that the home municipality lacked a youth clinic was associated with chlamydia, indicating that youth clinics may be a valuable contribution to lower the community prevalence of chlamydia among men. This is probably an indirect effect of diagnosing and treating young women as these are the overwhelming majority of users of these drop-in facilities that offer condoms and chlamydia tests free of charge for young people up to the age of 20
years. In Rogaland county, the majority of the municipalities do offer a local youth clinic. Perhaps also the mere visibility of such a clinic can contribute to a more protective behaviour among men. The finding should, however, be interpreted with caution because of the small group size reporting not having a local youth clinic in their home municipality.
Close to half of the men in our survey did not know if there was a youth clinic present in their municipality. This group had a lower chlamydia prevalence, only 2.1%. We may speculate that these men have less sexual risk behaviour and therefore never have felt the need to find out about youth clinics in their area. Alternatively, these men were more likely to take part in the study and use our mailed testing kits since they were not aware of the youth clinic with testing facilities nearby.
Among women, we found that having had chlamydia diagnosed previously was associated with an increased risk of current infection. This is consistent with findings from a substantial body of previous literature [31
]. 63% of the chlamydia positive women with a previous chlamydia diagnosis in our study had changed their sexual partner within the last 6
months. The temporal association between the previous infection and this positive test is, however, unknown. We can therefore not establish whether the positive test result represents treatment failure, lack of partner treatment or a new infection with a new sexual partner. Many factors could contribute to this result. Our results may indicate that sexual risk behaviour is persistent and that a chlamydia diagnosis may not lead to behavioural change. It highlights the need for guidance on safe sexual behaviour at the time of treatment, more careful partner tracing and treatment and a special need to target women with a previous chlamydia diagnosis in screening. On the other hand, women who had consulted their family doctor on STIs were less likely to have a current infection than those who had not consulted their family doctor. Possible explanations could be that women who consult their family doctor for STIs are those with less sexual risk behaviour or that they in fact have received good guidance on safe sexual behaviour from their doctor.
This cross sectional study was part of a clinical trial of a postal screening system for chlamydia in Norway. Only those who wanted to have a chlamydia test taken answered the questionnaire. The response rate is therefore lower than what would have been expected if the participants would only have to answer a questionnaire. The uptake of the screening offer was also lower than anticipated and what has been the case in similar studies[16
]. The low response rate raises the concern of a potential selection bias in our results. It is a cause for concern regarding the validity of the prevalence estimates. As we have no information on the non-responders, including their chlamydia status, we will not know if reasons not to participate in the study are the same as factors associated with infection. However, regarding the association between chlamydia and risk factors within the group of respondents, the overall response rate is less of a concern. The low response rate would lead to biased associations only if participation was associated with both
the risk factors in question, which is more unlikely.
The rather low number of participants and thereby chlamydia cases in our study gives the study limited power to detect associations between infection and exposures. We can therefore not exclude other associations than those detected by our study.
Questionnaires were filled out at the same time as the home sample was submitted. With this cross sectional study design we are not allowed to determine a causative effect of the different factors associated with infection. The relatively long recall period could cause misreporting of own risk behaviour. However, differential misclassification is avoided since infectious status was not known at the time the participants fill out the questionnaires.
On the other hand, by using postal recruitment and allowing participants to take the chlamydia test at home, we might have reached a broader part of the population than those seeking the health care service believing they are at risk.
Conclusion and recommendations
Young Norwegian men and women have their sexual debut at an early age and the majority do not use condom when having casual sex. We found a chlamydia prevalence of 5.5% in our population. The probability of infection increased with a greater number of partners, and among men the odds of infection increased if their home municipality lacked a youth clinic. For women having a previous chlamydia diagnosis increased the probability of infection while having previously consulted their family doctor decreased the odds of infection.
Only a very low proportion of the men in our sample had ever visited their local youth clinic. Our results indicate the importance of having a visible youth clinic in each municipality. It also suggests targeting women with a previous chlamydia diagnosis.