Schizophrenia Not Linked to Prenatal Exposure to Influenza
No association was found between schizophrenia risk and prevalence of influenza three, four, or five months prior to birth, during any month prior to birth, or during the month of birth. "[O]ur study does not support the hypothesis that in utero [in the womb] exposure to influenza or other common infections may increase the risk of developing schizophrenia", writes Westergaard.
"I think this is an excellent paper. The investigators use the Danish Registry Data which has been developed over decades which is just now bearing fruit for schizophrenia research", Ezra Susser, MD, DrPH, tells WebMD. "They looked at things rarely examined in schizophrenia research: birth order, sibship size, space between siblings. As far as the small interval between siblings, you can't make too much of the findings yet but they're really intriguing."
"They tested the influenza hypothesis in a much better way than previous studies," he says. Susser, the head of the Epidemiology of Brain Disorders program at the New York State Psychiatric Institute and Columbia University, was not associated with the Westergaard research.
Other experts aren't so sure. "This study casts further doubt that influenza is an important infection in causing later cases of schizophrenia. However, I take serious exception to the conclusion that in utero infections are not important," E. Fuller Torrey, MD, tells WebMD. "Increasingly research, including our own, has shown that infections both in utero or in early childhood may well play a role in later development of both schizophrenia and bipolar disorder." Torrey, who also is not associated with the study, is from the developmental neurovirology laboratory of the Stanley Research Foundation for Research in Schizophrenia and Bipolar Disorder in Bethesda, MD.
"It's important to stress that there is no database in the world as good as the database they are using, which consists of the entire population of Denmark, to answer the kinds of questions they're asking", says Torrey. "However, the big problem with these influenza studies is that it doesn't tell you whether the mother [of the schizophrenia patient] actually had it or not. You're not going to be able to measure what's going on in utero by measuring the incidence of maternal symptoms or infections in the community." He suggests there may be women who have influenza but do not report it to the medical authorities or perhaps are asymptomatic or only mildly symptomatic.
Torrey adds, "Pregnancy is like a black box. It's conceivable that there's a whole series of things going on, including infections, and we only have the vaguest idea of what's going on. We can only measure the most extreme ends of the spectrum."