Objectives: To examine whether high probability of exposure to influenza and influenza-like illnesses during pregnancy is associated with autism spectrum disorders.
Methods: The study included 5,487,491 children born in California between 1991 and 2001. The outcome was autism diagnosed before the child’s sixth birth date. Autism cases (n = 17,515) were identified from diagnoses recorded in databases of the California Department of Developmental Services in 1991 through 2008. Separately, we obtained individual level data on all admissions, statewide, for influenza and influenza-like illnesses (international code for diseases 480 – 488) from 1991 to 2002 from the Office of Statewide Health Planning and Development. Daily population rates of hospitalization for influenza and influenza like illnesses were calculated by county. These county rates were then assigned to each woman as a proxy of her level of exposure to influenza for several time periods during pregnancy assuming that high rates would lead to increased probability of infection. Multivariate logistic regression models were used to estimate odds ratios with their 95% confidence intervals for autism by rates of hospitalization.
Results: Maternal exposure to influenza defined as occurring any time during pregnancy was not associated with autism. However, maternal high probability of exposure to influenza during the first 8 weeks of pregnancy was associated with 8% (OR = 1.08 95% CI 1.03 – 1.13) increased risk of autism. No association was found with any other time window of pregnancy.
Conclusions: The results raise the possibility that early pregnancy may be a critical window when influenza infection or factors associated with influenza infection such as fever increases the risk of autism. Our results are similar to those previously reported on associations between maternal influenza infection and risk of schizophrenia.
See more of: Epidemiology
See more of: Prevalence, Risk factors & Intervention