A recent hypothesis postulates that obsessive-compulsive disorder and other mental illnesses may result from throat infections by streptococcal bacteria (strep throat); however, data in the literature has been controversial. A new study published in JAMA Psychiatry investigate the risk of mental disorders following strep throat infections and found that individuals with streptococcal infections had an increased risk for mental disorders and OCD.
Obsessive-compulsive disorder (OCD) is a mental disorder characterized by the need to perform certain routines repeatedly. These ritualistic actions often include counting things, checking things (such as whether a door is locked) or hand-washing. Often, these activities take up hours of the day and negatively impact the individual’s life. While the cause for OCD is unknown, there may be environmental and genetic components involved.
In recent years, childhood OCD and other tic disorders have been associated with throat infections by streptococcus bacteria (‘strep throat’). This hypothesis led to a term that encompasses mental disorders linked to streptococcal infection: Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infection (PANDAS). The suggested mechanism for this is molecular mimicry, whereby antibodies that the body makes to target streptococcal bacteria cross-react within the basal ganglia area of the brain. This is thought to occur because the antibodies and some neuronal proteins are similar in structure. This hypothesis has been supported by imaging studies which suggest inflammation in these parts of the brain in individuals with PANDAS. Additionally, some studies have found that immunotherapy has a positive effect on children with OCD/PANDAS.
Despite this, the PANDAS hypothesis is controversial as most studies are small and have many limitations, and a number of studies have not confirmed the hypothesis. In fact, some studies have found that streptococcal infections do not worsen neuropsychiatric symptoms in individuals with PANDAS.
A new study published in JAMA Psychiatry investigated the risk of mental disorders in children who had previous streptococcal throat infections. They monitored 1,067,743 children under the age of 18 for seventeen years. Of the children, approximately 349,982 had a positive result for a streptococcal test at least once.
The results of the study showed that children with streptococcal infections were at an increased risk for any mental disorder, particularly for OCD and tic disorders, compared to those without strep throat occurrences. Additionally, the risk for any mental disorder was elevated in those who experienced streptococcal infections. However, even individuals with a non-streptococcal infection were at an increased risk for developing mental disorders compared to those with no infections, indicating that the association may not be specific to streptococci.
The strengths of the study include the large cohort which was followed for seventeen years, making selection bias unlikely. Additionally, information on streptococcal tests were registered prospectively as they occurred, making recall bias unlikely as well. A limitation of the study is that some individuals may have had a streptococcal infection but did not receive a test to confirm the diagnosis; also that some individuals may have undiagnosed OCD or another mental disorder.
In conclusion, the study found that both individuals with streptococcal and non-streptococcal throat infections had an increased risk of mental disorders. However, the risk of mental illness and OCD was greatest in individuals with previous streptococcal infections. These findings support the PANDAS hypothesis but could also lead to alternative hypotheses.
Written By: Neeti Vashi, BSc