Introduction
Obsessive-compulsive disorder (OCD) is only moderately heritable1 2, but surprisingly little is known about potential environmental risk factors contributing to its aetiology.3 4
A potential environmental risk factor that has gathered considerable attention is infections, hypothesised to be causally related to OCD through postinfectious autoimmune processes. 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…
