Infections during childhood may contribute to a later diagnosis of intellectual disability (ID) and autism spectrum disorder (ASD), according to a new study.

While infections that occur during pregnancy are established causes of life-long behavioural and intellectual disabilities, few studies have investigated the relationship between infections in childhood and ID and ASD. The researchers therefore set out to fill this gap.

To do this, the authors of the study used data from a register-based cohort of more than 550,000 individuals born between 1987 and 2010, all of whom lived in Stockholm County. The researchers then followed the individuals from birth to their 18th birthday or December 31 2016.

The authors considered potential confounders such as family socioeconomic factors, obstetric complications, and parental histories of treatment for infection.

Childhood infections were overrepresented in individuals who were later diagnosed with an intellectual disability 

Of the 556,732 children included in the study, around half (50.8%) had at least one registered infection before age 18. The severity of these infections differed significantly between those who received specialised care for infection and those who did not.

Among those who were not diagnosed with an infection during childhood, 5,803 (2.1%) were diagnosed with ASD and 2,051 (0.7%) with ID. In comparison, of those who were diagnosed with one or more infection during childhood, 8,802 (3.1%) were diagnosed with ASD and 4,465 (1.6%) with ID.

While central nervous system (CNS) infections were rare compared to non-CNS infections, both types of infections were overrepresented in individuals with the investigated outcomes, particularly those with ID, as well as ID and ASD.

The study's findings cannot conclude that childhood infections are strongly associated with a later diagnosis of ASD 

The results suggest that specialised care for infections during childhood is common among individuals diagnosed with ID and/or ASD.

The researchers note, however, that: “It may be that children who are later diagnosed with ID or ASD have a higher liability to severe infections that contribute to the associations observed here but infections are not causing ID or ASD.

“It may also be that such an increased liability leads to increased exposure to severe infections, during critical periods, which adversely affect neurodevelopment.”

They conclude: “Based on our analysis of the timing of infections and diagnoses of ASD and ID in this study, including careful consideration of potential confounding by shared familial factors, we suggest that infections during early childhood contribute to risk of a later diagnosis of ID, including ID co-occurring with ASD.”

They note that the study's findings indicate "weak but significant" associations between childhood infection and autism spectrum disorder without an intellectual disability diagnosis, and more research will need to be done in future studies to determine this association.