“This higher risk held if they were hospitalized for an infection at any given age before the onset of schizophrenia,” said lead investigator Philip R. Nielsen, a Ph.D. candidate at the National Centre for Register-based Research, Aarhus University, Denmark.
The findings also showed an increased risk for schizophrenia if the child’s father had been hospitalized for infection.
“These are serious infections requiring hospitalization, so it is only the more severe cases of infections that are implicated here, and the fact that we found raised risk if the father had a history of being hospitalized for infection indicates that there may be some familial susceptibility to infection and subsequent schizophrenia risk,” Nielsen said.
“We know that we are dealing with a multifactorial etiology in the case of schizophrenia, so infection is probably not a single causal factor. The association between childhood infection and schizophrenia may be due to inflammatory responses affecting the brain, or genetic and environmental risk factors in certain families,” Nielsen said.
The research was presented at the 14th International Congress on Schizophrenia Research (ICOSR).
Although several studies have reported links between maternal infections during pregnancy and schizophrenia, few studies have investigated infections in children, and their results have been inconclusive, Nielsen said.
In the new study, researchers pulled data from two population-based registers — the Danish Psychiatric Central Register and the Danish National Hospital Register — and selected all individuals born in Denmark between 1981 and 2000, which totaled 843,390 individuals.
They then identified 3,409 individuals who had entered a hospital for the first time with schizophrenia between the years 1991 and 2010. Of these, 1549 were exposed to an infection during their childhood that required hospitalization.
Those who were hospitalized for infection during childhood were almost 50 percent more likely to develop schizophrenia than individuals who were not. Bacterial infection was associated with the highest risk. Viral infections increased the risk by 40 percent.
“There are several schools of thought in terms of the infection-based hypothesis of the link between infection and schizophrenia,” said Emily G. Severance, Ph.D., a schizophrenia expert at Johns Hopkins University School of Medicine in Baltimore, Md., who was not involved in the study.
“Perhaps it is something that occurs prenatally that affects the development of the neurons in the developing brain, or perhaps it happens postnatally, as in this study, when the brain is still developing. Infection could also disrupt synaptic connections,” Severance said. “There are a number of different risk factors associated with the immune system and schizophrenia.”