Brief report Birth month and depressive and suicidal symptoms in an elderly Australian sample born in the Southern or Northern Hemisphere Jon J. Pfaff a , Rebecca A. Bernert b , Daniel L. Hollar b , Tracy K. Witte b , Katherine A. Merrill b , Jeremy W. Pettit c , Osvaldo P. Almeida a , Thomas E. Joiner Jr. b, ⁎ a Unit of Geriatric Psychiatry, University of Western Australia, Perth, Australia b Department of Psychology, Florida State University, Tallahassee, FL 32306-1270, USA c Department of Psychology, University of Houston, Houston, TX, USA Received 3 February 2005; received in revised form 24 October 2005; accepted 20 April 2006 Abstract We examined the relationship between season of birth and depressive and suicidal symptoms among 859 elderly outpatients. Date and country of birth were recorded for each participant. Those in utero during the Northern or Southern Hemisphere flu peak were expected to show the highest depressive and suicidal symptoms. Hypotheses were partially supported. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Season of birth; Suicidal symptoms; Depressive symptoms 1. Introduction Research suggests that prenatal influenza exposure may constitute a neurodevelopmental risk factor for mental disorders in adult offspring. Specifically, reports indicate a significant association between in utero exposure to in- fluenza, particularly during the second trimester of gestation, and an increased risk for schizophrenia and major depression (Mednick et al., 1988; Machon et al., 1997). To some extent, however, evidence regarding this association remains mixed (Morgan et al., 1997). CNS development is well underway during the se- cond trimester of gestation. Neural organization entails a cascade of simultaneously occurring events during prenatal development (e.g. cell proliferation, migration, differentiation, death; axonal, dendritic outgrowth); the disruption of such processes is thought to result in either irregularly positioned neurons or fewer neurons, giving rise to altered neural functioning and abnormal behaviors (Nowakowski and Hayes, 1999). Preliminary research supports the proposed link. In mice, for example, in- fluenza exposure during the prenatal period affects the development of neurotransmitter systems and CNS mor- phology (Fatemi et al., 1998). In a previous report (Joiner et al., 2002), we de- monstrated a significant association between birth month (corresponding to peak flu season during the second trimester) and elevated levels of depressive and suicidal symptoms. This connection emerged in a sample of young adults born in either the Northern or Southern Psychiatry Research 144 (2006) 217 – 219 www.elsevier.com/locate/psychres ⁎ Corresponding author. Tel.: +1 850 644 1454; fax: +1 850 644 7739. E-mail address: joiner@psy.fsu.edu (T.E. Joiner). 0165-1781/$ - see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.psychres.2006.04.019