Children who acquired a TORCH infection in the womb were roughly three times more likely to be diagnosed with autism than children who did not, according to a Karolinska Institutet study published in JAMA Pediatrics this week. The same infections were linked to intellectual disability risk more than seven times higher, and up to 30 times higher for the most severe cases. Researchers stressed that the infections themselves are rare, transmitted from mother to fetus in only a small fraction of pregnancies, even as the relative risk they carry is large.
A tripled autism risk in a 3.7-million-person study
The research team, led by Karolinska PhD student Hugo Sjoqvist and senior researcher Reneé Gardner of the university’s Department of Global Public Health, tracked 3.7 million people born in Sweden between 1987 and 2021, identifying 975 who had been diagnosed with a congenital TORCH infection. Children in that group were approximately three times more likely to receive an autism diagnosis than the rest of the cohort, and more than seven times more likely to be diagnosed with an intellectual disability. Follow-up ran as long as three decades for the earliest births in the cohort, giving the team enough time to capture diagnoses that typically surface well after infancy.
For the most severe cases, the gap widened further: children with a congenital TORCH infection were up to 30 times more likely to be diagnosed with severe to profound intellectual disability, according to Karolinska Institutet’s own summary of the findings, which put the JAMA Pediatrics paper online this week. Sjoqvist described the dataset behind those figures as “the largest to date in this field,” based on “national register data covering almost the entire population of Sweden,” a framing echoed in ScienceDaily’s report on the findings.
Rare infections, outsized relative risk
TORCH is shorthand for a group of infections — toxoplasma, rubella, cytomegalovirus, herpesvirus and, in some classifications, syphilis — capable of crossing the placenta and reaching a developing fetus, unlike most infections a pregnant woman might pick up. Gardner was direct about how uncommon that crossing actually is: “It is unusual for these infections to be transmitted from mother to child,” she said, adding that the infections “account for a very small proportion of all cases of autism.”
That rarity showed up in the study’s population-level math. Despite the roughly threefold and sevenfold relative risks, congenital TORCH infections accounted for only about 0.034% of Sweden’s autism cases and 1.2% of its severe intellectual disability cases, meaning the vast majority of both conditions in the cohort had nothing to do with a prenatal infection.
Cytomegalovirus is the biggest driver
Among the TORCH pathogens, cytomegalovirus is by far the most common cause of congenital infection. The Centers for Disease Control and Prevention estimates that about 1 in 200 newborns in the United States is born with congenital cytomegalovirus, and roughly 1 in 5 of those infants will have birth defects or long-term health problems, making it the country’s leading infectious cause of birth defects. The CDC’s page on congenital infection lists hearing loss as the most common lasting effect, alongside possible brain, liver, spleen, lung and growth problems.
An NIH-hosted clinical reference on the TORCH complex puts overall congenital infection rates for the group at roughly 2 to 3 percent of all congenital anomalies, with maternal CMV and toxoplasmosis together affecting an estimated 2 to 10 births per 1,000 — figures that frame just how much smaller the 975-case Swedish sample is relative to the 3.7 million people studied.
Why researchers ran a sibling comparison
To test whether the elevated risk reflected the infections themselves rather than shared family or genetic factors, Gardner’s team compared outcomes among siblings, a design meant to control for characteristics that run in families regardless of any single pregnancy’s infection status. The elevated risks held up under that comparison, according to the Karolinska release, reinforcing the infection link rather than an unrelated family trait.
Gardner framed the public health case for the finding around prevention rather than alarm, noting that “some of them can be prevented, which makes them important from a public health perspective.” Cytomegalovirus has no approved vaccine, but rubella has been preventable through routine childhood immunization for decades, and toxoplasmosis risk can be reduced through food-safety and hygiene precautions during pregnancy.
The study leaves open how a fetal TORCH infection biologically shifts neurodevelopment, an area Sjoqvist’s team said future work — following the same Swedish registers forward — is positioned to pursue given the size and duration of the national data already assembled.
Sweden’s national health registers made the sibling design possible in a way few countries could replicate, since researchers needed birth, diagnosis and family-linkage records covering close to a full generation to find enough sibling pairs where only one child had a documented infection. That infrastructure is also why the 975 identified cases, though small next to 3.7 million total births, produced statistically stable risk ratios rather than estimates built on a handful of anecdotal cases.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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