Season of Birth and Schizophrenia in Northeast Brazil: Relationship to Rainfall

Abstract: Although the association of schizophrenia and winter birth has been replicated many times in the Northern hemisphere, studies in the Southern hemisphere have been less consistent in their findings. A study from NE Brazil indicated the period between May and July, 3 months after the peak in rainfall, as a risk period for schizophrenia birth. We report findings from a random selection of charts (N = 1789) from the only public inpatient psychiatric facility in Ceara, Brazil (2° to 5° S). We compared the seasonality of birth in the schizophrenia group (N = 406) to multiple control groups: (1) psychosis not otherwise specified (N = 868), (2) other psychiatric diagnoses (N = 515), and (3) the average monthly birth rate in the general population. Patients with schizophrenia had a significantly greater risk of being born in the risk period compared with any of the control groups. There is a significant association between rainfall in a month and schizophrenia births 3 (p = 0.03) and 4 months (p = 0.01) later. This study corroborates findings of a significant seasonality in schizophrenia births in northeast Brazil.