News · Brain & Mental Health
Congenital CMV and other TORCH infections tied to 3 times the autism risk
Infections passed from mother to baby during pregnancy are rare, and doctors have long known they can injure a developing brain. A study of 3.7 million Swedes puts numbers on autism and intellectual disability.
- An observational study of 3,666,002 people born in Sweden in 1987 to 2021, 975 with a congenital TORCH infection.
- TORCH covers toxoplasmosis, syphilis, rubella, cytomegalovirus (CMV) and herpes simplex, passed from mother to baby.
- Affected children had about 3 times the risk of autism and 7 times the risk of intellectual disability.
- Comparisons with their own brothers and sisters gave similar or stronger results.
- These infections are rare, and only babies with diagnosed, symptomatic infections were counted.
Some infections can pass from a pregnant woman to her baby, and a few can harm a growing brain. Doctors group the main ones as TORCH: toxoplasmosis, syphilis, rubella, cytomegalovirus (CMV) and herpes simplex. How much they add to autism across a whole population has been hard to measure, because they are rare.
A study in JAMA Pediatrics used Swedish national registers covering 3.7 million births. Children born with a diagnosed TORCH infection had about three times the risk of autism, and the link held up when they were compared with their own siblings.
What autism is and where infections fit in
MedlinePlus describes autism spectrum disorder (ASD) as a neurological and developmental disorder that begins early in childhood and lasts throughout a person’s life. On its causes it is candid: the causes of ASD are not known, though research suggests that both genes and environment play important roles.
Infections before birth are one of the environmental factors with the strongest biological case. The authors describe congenital TORCH infections as established causes of severe fetal injury, but note that their population-level contribution to neurodevelopmental and psychiatric outcomes had not been pinned down.
How the Swedish TORCH study worked
The researchers linked Sweden’s health, birth, school and death records for everyone born there from 1987 to 2021. They followed them to the end of 2023. Among 3 666 002 individuals born in Sweden, 975 had a clinically diagnosed congenital TORCH infection.
They compared those children with everyone else, and then with their own brothers and sisters. Siblings share much of their genes and upbringing. A link that holds up within families is less likely to come from family background.
What happened to autism and intellectual disability
The risks were raised for both conditions. Congenital TORCH infections were associated with increased risks of intellectual disability, at about seven times the usual rate, and of autism, at about three times. Within families, the gaps were similar or larger.
The pattern had a gradient. Risk climbed with the severity of intellectual disability, and autism accompanied by intellectual disability showed a much stronger link than autism without it. Affected teenagers also had lower school grades at 16, suggesting effects below the threshold of a diagnosis. There was no consistent link with obsessive-compulsive disorder, and the link with ADHD weakened within families.
Why these infections matter despite being rare
For one family the numbers are stark. Across Sweden, though, these infections touched fewer than one birth in 3,000, so they explain only a small part of autism overall. What they offer is a cause that can partly be prevented or treated.
The authors put it plainly: the findings underline the importance of preventing specific vertically transmitted infections, meaning those passed from mother to baby. Rubella is largely prevented by vaccination, syphilis is found by routine screening in pregnancy and treated, and CMV is the most common of the group, with prevention resting mostly on hygiene.
What a register study of infections cannot show
The study counted only infections that were diagnosed because they caused symptoms. Sweden does not screen newborns for these infections, so babies with silent infections, which are common with CMV, were not included, and their risk may be different.
About 200 infections were diagnosed after the first year of life, sometimes after hearing loss or another problem prompted testing. That could inflate the links, but the authors report that leaving those cases out did not change the results. Register data also record diagnoses rather than how each child actually functions, and the findings come from one country’s health system.
What this changes for pregnancy care
For people who are pregnant or planning a pregnancy, the practical steps are the familiar ones: keep rubella vaccination up to date before pregnancy, attend routine screening, and ask about CMV. Advice on handwashing after contact with young children’s saliva and diapers, and on food and cat litter hygiene, targets the most common routes.
For health systems, the study strengthens the case for looking harder at CMV in particular, including whether wider newborn testing would help children get earlier support. It does not suggest that autism in general comes from infections.
People also ask
What did the study find?
Congenital TORCH infections were associated with intellectual disability (hazard ratio 7.22, 95% CI 6.14 to 8.49) and autism (3.10, 2.55 to 3.76), with similar or greater estimates in sibling comparisons (11.28 and 3.19). Risk rose with severity, from 3.01 for mild to 23.51 for severe to profound intellectual disability, and was higher for autism with intellectual disability (6.23) than without (1.97). School grades at 16 were 1.50 points lower.
What does TORCH stand for?
Toxoplasmosis, other infections such as syphilis, rubella, cytomegalovirus and herpes simplex. They are infections a mother can pass to her baby during pregnancy or birth.
How common are these infections?
Diagnosed cases are rare: 975 among more than 3.6 million births in this study. Many CMV infections at birth cause no symptoms and are never diagnosed, and those were not counted here.
Does this mean infections cause most autism?
No. The causes of autism are not fully known and involve genes and environment. These infections affect very few babies, so they explain a small share of autism overall even though the risk for an affected child is raised.
Why compare siblings?
Brothers and sisters share much of their genetics and home environment. If the link holds up within families, it is less likely to be explained by those shared factors.
What can pregnant people do?
Ask your midwife or doctor about screening and prevention. Standard advice includes careful handwashing, especially after contact with young children, and food and pet hygiene. This is general information rather than medical advice.