A group of rare infections passed from mother to child during pregnancy roughly triples a child’s risk of an autism diagnosis, according to the largest study of its kind, published Sept. 23 in JAMA Pediatrics. Researchers stress the infections remain uncommon and explain only a small share of all autism cases, but for the children affected, the added risk is substantial.
The study, led by Hugo Sjoqvist and Renee M. Gardner at Sweden’s Karolinska Institute, tracked nearly 3.7 million people born in Sweden between 1987 and 2021 using national health records, comparing outcomes for the 975 who were diagnosed with a congenital TORCH infection against the general population, including sibling comparisons to rule out shared family factors. TORCH is shorthand for toxoplasmosis, “other” infections, rubella, cytomegalovirus and herpes, all of which can cross the placenta and affect a developing fetus.
Children with a TORCH infection were about three times more likely to be diagnosed with autism than their peers, the study found, and roughly seven times more likely to have an intellectual disability. For severe to profound intellectual disability, the risk climbed 30-fold. Close to one in five children born with a TORCH infection went on to develop autism. Despite those steep relative risks, the infections are rare enough that they account for less than 0.04 per cent of autism cases and about 1.2 per cent of severe intellectual disability cases in the study population.
“This study is the largest to date in this field and is based on national register data covering almost the entire population of Sweden,” Sjoqvist said. Gardner added that while TORCH infections “account for a very small proportion of all cases of autism in the population,” the children who are affected show “a clearly elevated risk.”
The findings land in the middle of an unresolved debate among Canadian doctors over how aggressively to screen for these same infections. Canada does not test pregnant women for toxoplasmosis or cytomegalovirus as a matter of routine. Standard prenatal bloodwork, as laid out by Public Health Ontario and mirrored in most provinces, screens only for HIV, syphilis, rubella immunity and hepatitis B. A 2023 clinical review in the Journal of Obstetrics and Gynaecology Canada went further, explicitly recommending against routine toxoplasmosis screening for most of the country, arguing it would trigger costly follow-up tests without improving outcomes, though the same review said first-trimester cytomegalovirus screening can be worthwhile for identifying risk.
Newborn screening for congenital cytomegalovirus, meanwhile, is a patchwork across the country. Alberta, Saskatchewan, Manitoba and Ontario test every newborn’s blood spot for the virus, while British Columbia, New Brunswick and Nova Scotia test only babies who fail a hearing screen or already show symptoms. Quebec has explicitly rejected universal newborn screening, citing insufficient evidence it improves outcomes and a risk of over-diagnosing infections that would never have caused harm.
The Swedish data does not settle that argument, since it does not evaluate whether earlier detection through screening actually changes a child’s outcome. But it adds fresh weight to the case that these infections deserve more attention where they are found, even as most of the country continues to leave testing to clinical judgment rather than routine protocol.
The autism question also lands against a shifting backdrop at home. The Public Health Agency of Canada’s most recent national survey found one in 50 Canadian children and youth aged one to 17, or two per cent, had an autism diagnosis, a figure the agency itself says likely undercounts the true prevalence. Service-access data from British Columbia put the rate even higher, at one in 37 children by 2020, up from one in 66 in 2015.
None of that broader rise is explained by TORCH infections, which the Swedish researchers say remain a minor contributor to autism overall. What the study does offer is a rare, population-scale answer to a narrower question that has followed families of children with congenital infections for decades: how much did this specific illness shape what came next. For most of the roughly 3.7 million people in the study, the answer was little to nothing. For the 975 who had a TORCH infection, the odds shifted considerably.
Via JAMA Pediatrics and CP24. Read the original: CP24, “TORCH infections linked to ‘very small portion’ of autism cases: study”
