A new study finds that hospital-diagnosed bacterial infections in pregnancy are associated with a higher risk of autism spectrum disorders.

Researchers from the Kaiser Permanente Division of Research report their findings in the Journal of Autism and Developmental Disorders.

The study brings new evidence on the role of infection in autism spectrum disorders (ASDs) and suggests further areas to explore.

For their analysis the researchers matched records of 407 children with autism and 2,075 children who did not have autism. The children were born between 1995 and 1999 and were members of the Kaiser Permanente health plan for at least 2 years following their birth.

Senior author and research scientist Dr. Lisa A. Croen says they found:

Infections diagnosed in a hospital setting were more common among mothers of children who developed an ASD compared with mothers of children who did not develop an ASD.”

She explains that though infections in pregnant women are common, they found most were not tied to increased risk for autism:

“Only bacterial infections diagnosed in the hospital were associated with an increased risk.”

Their analysis showed pregnant women with bacterial infections diagnosed in the hospital (such as of the genitals, urinary tract and amniotic fluid) had a 58% higher risk of delivering a child with ASD.

Although not very common in the group they studied, having an infection diagnosed during a hospital stay that occurred in the second trimester of pregnancy was linked to a three-fold increase of having children who developed ASD.

Lead author and research fellow Dr. Ousseny Zerbo says:

“Infections diagnosed in an inpatient setting may represent more severe infections, and these were associated with increased risk of ASD.”

Although it is not clear how infection in the mother affects risk of the child developing autism, Dr. Zerbo says animal studies suggest it could be something to do with how the expectant mother’s immune system reacts to infection. It may interfere with brain development in the fetus.

For instance, a recent study of mice and rats found that viral infection disrupts neural development in offspring, increasing risk of autism.

Dr. Zerbo says their study shows most infections in pregnancy are not linked to autism, but he cautions there does appear to be some increased risk and advises:

“It would be prudent for pregnant women to contact their doctor if they suspect an infection.”