The proper treatment of curable sexually transmitted infections (STI) is one of the most important aspects in the control and prevention of disease and could be affected by patients’ psychological status. Depression often occurs after a stressful event, which might include STI. STI is subject to stigma1 2 and so is depression.3^–9 Depression might interfere with getting treatment by decreasing the patient’s support.6 Depressed patients are also more vulnerable to sickness; they tend to have increased lymphocyte apoptosis resulting in a decrease in the total number of T lymphocytes (CD3⁺), T helper cells (CD4) and natural killer cells (CD16⁺) compared with healthy individuals.10

It has been demonstrated that behavioural intervention can significantly reduce the number of unprotected sexual encounters as well as the incidence of STI.11 The existence of depression or mental disorders limits the success of behaviour counselling strategies for STI patients. To determine the association between STI and depression has important public health implications in the control and prevention of curable STI. In this study, we analysed data from a national survey and examined the prevalence of STI associated with depression in the Canadian general population and discuss potential mechanisms for the association.

METHODS

The present analysis was based on data from the Canadian Community Health Survey conducted by Statistics Canada between January and December 2003.12 The target population of the survey were household residents aged 12 years or older in all 10 provinces and three territories in Canada, excluding individuals living on Indian reserves or crown lands, clientele of institutions, full-time members of the Canadian armed forces and residents of certain remote regions.

The national survey used a multistage stratified sampling design, with each dwelling as the final sampling unit. In each household, some limited information was collected from all household members. One or two people per household were asked to complete an in-depth interview. A total of 134 072 persons aged 12 years or older participated in the survey, which represents 80.7% of the population selected. Only individuals 15–49 years of age were asked to complete the sexual behaviour module. Of 63 970 individuals aged 15–49 years, 56 913 answered “yes” to the question “Have you ever had sexual intercourse?” Among those who ever had sexual intercourse, 54 638 participants provided either a “yes” or “no” response to the question, “Have you ever been diagnosed with a sexually transmitted disease?” A comparison between people who did and did not answer the questions about sexual intercourse and STI showed no significant differences in sex, age, marital status, socioeconomic status, smoking, alcohol drinking, immigrant status and chronic conditions. The depression scale was included in an optional topic module and only those living in the provinces of Newfoundland, New Brunswick, Prince Edward Island, Ontario, Alberta and Yukon Territory were administered this optional province-wide module. The characteristics of the subjects living in these provinces were comparable to those living in provinces without the mental health module except for immigrant status. As a result, 21 560 subjects 15–49 years of age who had ever had sexual intercourse and lived in the above-mentioned provinces and territory were included in the current analysis.

For depression, the survey included a set of 27 questions about symptoms of depression based on an approach proposed by Kessler and Mroczek.13 These items were taken from the Composite International Diagnostic Interview, and were used in the survey to record major depressive episodes (MDE) experienced by respondents in the past 12 months.13 14 The Composite International Diagnostic Interview is a structured diagnostic instrument designed to represent the definitions and criteria of both the Diagnostic and Statistical Manual of Mental Disorders and the diagnostic criteria from research of the International Classification of Diseases, version 10.14 Depression scores range from zero to eight, indicating increasing probability of a depressive disorder. Scores of five or more were taken to identify a clinical MDE in the previous 12 months, which corresponds to a 90% likelihood of a positive diagnosis of MDE.12

Based on total household income adjusted for the number of household members, subjects were classified into low (<US$30 000 with one or two people; <US$40 000 with three or four people; <US$60 000 with five or more people), middle (US$30 000–59 999 with one or two people, US$40 000–79 999 with three or four people, US$60 000–79 000 with five or more people), or high-income groups (US$60 000+ with one or two people, US$80 000 with five or more people). Subjects were grouped into three educational categories: low education (not proceeding beyond secondary school), middle education (secondary school completed with or without some post-secondary education) and high education (post-secondary school certificate or diploma). Current smokers were respondents who had smoked at least 100 cigarettes during their lifetime and reported smoking cigarettes every day or almost every day at the time of the survey. Former smokers were those who reported smoking cigarettes daily in the past but were not smoking at the time of the survey. Otherwise, subjects were classified as non-smokers. Other variables included in the analysis were age, immigrant status (yes or no) and the number of chronic diseases they had.

The prevalence of depression was calculated according to a history of self-reported STI and other factors. A logistic regression model was used to examine the association between depression and STI history after taking confounding factors and effect modifiers into consideration. Model parameters were estimated by using the method of maximum likelihood and were tested for significance by using the Wald statistic. All the variance estimates accounted for the multiple stage and stratified survey design. A population weight was calculated for each participant by Statistics Canada, which can be explained as the number of people that he or she represented in the Canadian population. This weighting takes into account the patterns of missing data and the oversampling of some strata. The effect of the complex survey design on variance estimates is summarised as a design effect and the design effect is the ratio of an estimated variance based on the survey to a comparable estimate of variance from a simple random sample of the population. Standard errors were inflated by this average design effect.15 First, population weights were divided by the average weight for all subjects included in the analysis. The sum of these relative weights is the effective sample size. Next, we divided the relative weights by the square root of the average design effect. All the statistical analyses were conducted using SAS 9.1.

RESULTS

Of the individuals 15–49 years of age who had had sexual intercourse, the overall prevalences of STD and depression were 5.3% and 7.9%, respectively. Table 1 shows the crude prevalences of STD and depression according to individual characteristics. Women had higher prevalences of both STI and depression than men.

People who were married or had a common law relationship, lived in larger households, were non-smokers, had higher education or income or were non-immigrants, or those with no chronic conditions were at lower risk of depression (table 1). Single, widowed, divorced, or separated people or those who tended to live alone, were smokers, had lower income, were non-immigrants, had chronic diseases or were alcohol users were at higher risk of getting STI (table 1). There was no association between education and self-reported STI.

Table 2 shows the association between STI and depression stratified by individual characteristics in men before and after adjustments for other variables. STI history was significantly associated with depression in men younger than 35 years but the association was not significant in those aged 35 years or older (age and STI interaction p<0.01). The association tended to be stronger in men who had higher income (p<0.01). Overall, the adjusted odds ratio for STI associated with depression was 1.5 (95% CI 1.1 to 2.2) for men.

The association between STI and depression was relatively consistent across the strata of individual characteristics in women (table 3). There was an association between STI history and depression that was similar in young and older age groups. There were no noticeable variations in the relationship between STI and depression associated with personal characteristics. The adjusted odds ratio for STI associated with depression was 1.8 (95% CI 1.4 to 2.3) for women.

DISCUSSION

Our results from a national survey support the argument that there is an association between STI and depression. Although women have a slightly higher frequency of STI and depression than men, our data show that the association existed in both sexes. This association was, however, modified by some sociodemographic factors in men.

Whereas the significant association between STI and depression was observed in both age groups in women, it was only observed in men younger than 35 years but not in those aged 35 years and older. An STI has the most devastating effect on the stability and trust of long-term relationships. A possible reason for depression associated with STI in older women and not older men is because of shame due to double standards, in which promiscuity in women is accepted to a lesser degree by society compared with men.16 Related to the observations, single men had a significant association between STI and depression but not married or common law men. However, both single and married or common law women had a significant association. Perhaps this may also be explained by the double standard argument referred to above.

A history of STI was associated with developing depressive symptoms and a history of depression was associated with a new STI in boys but not in girls.17 This bidirectional association could also exist in young male adults. The different association between boys and girls could be due to the different ways of expressing psychological distress.18 Whereas girls with depressive disorders tend to exhibit classic symptoms of social withdrawal and diminished interest in pleasurable activities, boys with psychiatric symptoms are more prone to engage in acting out behaviours, which may include sexual behaviours that increase the risk of acquiring an STI.18

There were other factors impacting the association between STI and depression in men, whereas the association was relatively consistent in women. Income and education are important modifiers for the association in men, which was significant for those with high education or high income, but not for the low or middle education/income groups, although the interaction between STI and education was not statistically significant on a multiplicative scale. One explanation is that high education and income levels tend to be correlated with higher job positions, which are strong role models. Revealing that they have STI may result in embarrassment because STI is a taboo in society, with suggestions of immorality, which may jeopardise the high position they work so hard to maintain.19 Research suggests that the longer and more committed a person works to obtain something the harder they try to keep it, a phenomenon known as cognitive dissonance.20 As individuals with higher education will have worked harder than others with low education for a job, they may tend to be more depressed when they have been diagnosed with an STI out of embarrassment and fear of losing what they worked so hard to achieve because of the stigma associated with STI. Another argument is that men with higher education have more knowledge about STI, which may cause some men to be more embarrassed about knowing they were foolish to have unprotected sex and they know more about the potential dangers of STI, which may cause them to be depressed.

There tend to be stronger associations of STI with depression in former smokers than non-smokers and current smokers for men; this difference was not observed for women. Men more than women consider smoking as a good way to make friends, to look macho and for social bonding. Former smokers may lose these benefits of smoking when they have an STI and may feel depressed.21 Current smokers may see smoking as a way of looking macho for a positive impression and do not want to believe anything terrible would happen, therefore an STI may not worry them as much.22 In contrast, smoking in woman is generally related more to emotional problems than in men because “women more often use cigarettes as a buffer against negative feelings, whereas men appear to smoke more habitually, or to increase positive feelings”.23 Woman are more likely to smoke due to depression.24 People who quit smoking are more likely to be those who have a better understanding of the health hazards of smoking and care more about their health than current smokers. Having an STI may have a greater impact on their mental health.

Having an STI is associated with anxiety, with an odds ratio of 1.91 and there is also a strong association between depression and anxiety. After adjusting for depression the association between STI and anxiety was no longer significant. The association between STI and depression did not change when anxiety is included in the model, indicating that the STI and depression is not likely to be mediated through anxiety.

This study has several limitations. First, the data were self-reported; there is no means to ensure the truthfulness of the response. The second limitation is that we did not know how religion and other cultural backgrounds influenced the relationship between STI and depression. We suggest that cognitive dissonance, the uncomfortable tension that comes from holding two conflicting thoughts at the same time, or from engaging in behaviour that conflicts with one’s beliefs, may become a factor because in many traditional cultures and religions premarital sex is forbidden.25 The action of premarital sex conflicts with an individual’s beliefs of sex after marriage in many cultures. This tension in one’s mind may be the reason for depression in some people.

The third limitation is that we did not take into consideration the type of contraceptive used. Most of the time, it is the women who do not have a say in the type of contraceptive used because they may be abused by their partners. Research showed in a survey in 1998 that approximately one in four women has experienced some form of assault/rape by an intimate partner.26 Most abused women fear more violence for trying to negotiate for safe sex and are more likely to incur abuse for a request for a condom.27 This abuse usually results in fewer negotiations for safer sex, multiple sex partners, higher suicide rates, substance abuse, anxiety and depression.27 The abuse may thus be associated with the depression and the STI may be an independent consequence of the abuse and may not be associated with the depression. The fourth limitation is that sexual orientation was also not included in the study. Gay and bisexual men engage in risky sexual behaviours and are more likely to get STI.28 Due to stigma and homophobia these individuals may still feel inferior as they may be confused about their gender identity, which may lead to depression.28 Therefore, their depression is probably associated with stigma about the patient’s sexual orientation instead of having an STI. In addition, because of the cross-sectional nature of the study, we cannot assume a causal relationship between STI and depression. There is also a possibility that depressed people are more likely to catch an STI. As the survey asked questions about “ever” STI and “recent” depression, however, it is more reasonable in this discussion to assume that an STI results in depression.

Even with these limitations, the significance of our study revealed an association between STI and depression, and this association varied according to other factors including age, income, education and smoking status in men, but was relatively consistent among female subpopulations. STI health clinics should be aware of which groups of STI patients are likely to have depression. Outreach programmes should also be designed accordingly to tackle the depression problem among STI patients.