Abstract
Background
Common infectious agents, such as Toxoplasma gondii (T. gondii) and several human herpes viruses, have been linked to increased risk of self-harm. As the infections may be prevented and treated, information on the possible association on common infections and suicidal outcomes may help prevent self-harm. We aimed to investigate the associations between self-harm and seropositivity to T. gondii, Epstein-Barr virus (EBV), Herpes Simplex virus Type 1 (HSV-1), and Cytomegalovirus (CMV). As depression is a major risk factor for suicidality, we also investigated whether being seropositive to the studied herpes viruses was associated with depressive symptoms.
Methods
IgM and IgG antibodies to T. gondii, EBV, HSV-1, and CMV were measured in a large Finnish population survey, the Health 2000 project, in year 2000. The 6250 participants were followed for 15 years via health care register and causes of death register. In addition, lifetime suicidal ideation and suicide attempts were assessed in a smaller subsample of 694 participants, based on systematically-evaluated self-report, medical records, and register data. The participants in the subsample were screened for possible psychotic symptoms or were controls; we controlled for this screen status in the regression models.
Results
We found no significant cross-sectional associations between baseline depressive symptom and the herpes infections, when controlling for background variables related to infection seropositivity. During the follow-up, 18 of the 6250 participants (0.3%) had either died by suicide or had a self-harm diagnosis. In Cox regression models, serological evidence of lifetime or acute infections was not found to be associated with these suicidal outcomes. In the subsample, 31% had had suicidal thoughts and 13% had attempted suicide. There were no significant associations between suicidal thoughts and infection seropositivity / antibody levels. However, those seropositive for IgG class antibodies for CMV, measuring latent infection, had fewer suicide attempts compared to those seronegative in multinomial logistic regression models adjusting for gender, age, education, childhood family size, regional residence, and screen status (OR for multiple attempts compared to no attempts =0.45, 95% confidence interval 0.22‒0.91, p=.026). Genders were investigated separately in post-hoc analyses and there were significant associations only in males: suicide attempts were associated negatively with CMV and positively with EBV. Looking separately at diagnosis groups, the CMV association was significant among those with a mood disorder and not among those with a psychotic disorder. C-reactive protein (CRP) measuring inflammation seemed to explain some but not all of the associations.
Discussion
In a large sample nationally representative of the whole Finnish adult population, antibodies to CMV, EBV, or HSV-1 were not associated with depressive symptoms. Seropositivity or antibody levels of T. gondii or herpes viruses were not associated with risk of subsequent death by suicide or intentional self-harm diagnoses at a 15 year follow-up. In the subsample consisting mostly of participants with severe mental disorders, in males, EBV antibody level was associated with a history of a suicide attempt and none of the other infection variables were associated with a heightened risk for suicidal thoughts or acts. We found a heightened risk for multiple suicide attempts in persons belonging to the CMV seronegative minority. This “protective effect” of being infected with CMV calls for further research.
Longitudinal associations between adolescents’ trajectory membership of depressive symptoms and suicidality in young adulthood: a 10-year cohort of Chinese Wenchuan earthquake survivors
