ORLANDO – Infections before the age of 4 are linked to the risk of nonaffective psychosis (NAP) in adulthood, according to a study presented at the annual congress of the Schizophrenia International Research Society. Researchers also found that a lower IQ seems to make the psychosis risk more likely.
It’s well-established in the literature that infections are tied to schizophrenia and that a premorbid IQ deficit is linked as well. Researchers looked to a huge data pool from the Swedish population to try to better define these risks.
“We know that there is an association between infection and schizophrenia,” said, head of the inflammation and psychiatry research group at the University of Cambridge (England). “We know that there is premorbid IQ deficit in schizophrenia. So, we wanted to know, is there a sensitive period during childhood when exposure to infection is more harmful?”
Researchers analyzed data for 647,000 people in the Swedish population who were born between 1973 and 1997, and conscripted for military service through 2010. Exposure to infection was considered to be any hospitalization with any serious infection between birth and age 13. IQ measurements were taken during military conscription at the age of 18. And researchers looked for risk of nonaffective psychosis from the age of 18 on.
There was a significant increase in risk of nonaffective psychosis in adulthood among those who’d had an infection, with a hazard ratio of 1.16 (95% confidence interval, 1.08-1.24). But when researchers broke down this risk into smaller age spans, they found that only infection between birth and 1 year old (HR, 1.19; 95% CI, 1.06-1.33) and between age 2 and 4 (HR, 1.11; 95% CI, 1.02-1.22) was linked with a significantly elevated risk of NAP. Researchers also saw a link between infection and IQ.
Researchers assessed whether familial factors could be confounding this link. They looked at rates of NAP among those with an early infection and no early infection in the general population and found that it was no different statistically than among full siblings with an early infection, compared with those with no early infection. In other words, the infection-psychosis risk was the same – whether someone was a close family member or not.
Dr. Khandaker said the findings more definitively establish a link between infection and psychosis risk and suggest that the early years are when children are at their most vulnerable.
“The association between adult nonaffective psychosis with premorbid IQ and childhood infection are not explained by shared familial confounding,” he said. “So these associations could be causal.”
When they looked at the role of IQ and the link between infection and psychosis risk, researchers found an interaction: With every 1-point decrease in IQ score, there was a corresponding increased risk of NAP among those with childhood infections (odds ratio, 1.006; P = .02).
“Childhood infections,” Dr. Khandaker said, “increase psychosis risk partly by interfering with neurodevelopment, and partly by exaggerating the effects of cognitive vulnerability to psychosis.”
Dr. Khandaker disclosed no relevant financial relationships.