Birth Seasonality and Schizophrenia

In Reply.—  We recently reported that the exaggerated winter birthrate for schizophrenics was strongest in those patients who never married and were born during winters following years with high pneumonia, influenza, or diphtheria rates.¹ We noted that the reason for this relationship is unclear but the data have suggested that these diseases may increase the risk for schizophrenia. Dr Ulwelling believed that our data (1) contradict the view that infectious diseases increase the risk for schizophrenia, (2) indicate that summer diseases protect against schizophrenia, and (3) support his theory that the winter birthrate excess is specific to affective disorders. He discounted the possibility that infectious diseases predispose the fetus to schizophrenia because most babies born in these winters were conceived after prior-year outbreaks ended. However, we believe that this observation does not argue against the existence of such relationships; rather, it suggests that any such connections are subtle or complex.In