Association between severe childhood infections and subsequent risk of OCD is largely explained by shared familial factors

• Published in: BMJ mental health 2024-10, Vol.27 (1), p.e301203
• Main Authors: Pol-Fuster, Josep, Kuja-Halkola, Ralf, Fernández de la Cruz, Lorena, Brikell, Isabell, Chang, Zheng, D’Onofrio, Brian M, Larsson, Henrik, Lichtenstein, Paul, Beucke, Jan C, De Schipper, Elles, Mataix-Cols, David
• Format: Article
• Language: English
• Subjects: Bacterial infections; Child & adolescent psychiatry; Letter; Obsessive compulsive disorder; PSYCHIATRY; Siblings; Teenagers; Viral infections
• ISSN: 2755-9734; 2755-9734
• DOI: 10.1136/bmjment-2024-301203

While some population-based studies have shown an association between infections and OCD, a common limitation of these studies is the lack of control for familial confounding, making causal inference impossible.5 6 A recent genetically informative population-based study concluded that the association between severe childhood infections and subsequent OCD may be largely explained by familial confounding.6 However, the coverage of infections was incomplete because this study restricted the exposure period to the first 3 years of life and only focused on very severe infections requiring hospitalisation.7 The current sibling-controlled cohort study aimed to further investigate the association between childhood infections recorded before age 12 years (the typical age of onset of childhood OCD) and the subsequent risk of OCD, including infections treated in both inpatient and specialised outpatient settings. OCD was defined as the first recorded instance of a diagnosis (ICD-9: 300D; ICD-10: F42) in the NPR after the age of 6 years, hence minimising the risk of diagnostic misclassification.1 Table 1 Distribution of study cohort characteristics No record of OCD (n=2201 394) n (%) OCD (n=24 992) n (%) Sex Male 1133 683 (51.5) 10 488 (42.0) Female 1067 711 (48.5) 14 504 (58.0) Birth year 1987–1991 554 395 (25.2) 7734 (31.0) 1992–1996 522 442 (23.7) 6863 (27.5) 1997–2002 522 552 (23.7) 6687 (26.8) 2003–2008 602 005 (27.4) 3708 (14.8) Any infection*†‡ 608 851 (27.7) 7059 (28.2) Bacterial infections† 391 302 (17.8) 4472 (17.9) Viral infections‡ 336 176 (15.3) 3939 (15.8) *Swedish International Classification of Diseases, 9th edition (ICD-9) codes: 466A 466B 478B 478C. To examine the association between childhood infections and the subsequent risk of OCD, we performed Cox proportional hazards regression analyses with first infection as time-varying exposure and age as the underlying time scale to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.