Does depression lead to influenza? - A systematic literature analysis

Background: Depressive disorders affect approximately 18.8 million patients annually. Influenza, a preventable infectious disease, leads to 50 million new cases each year and up to 40,000 deaths annually. It is believed that depressive symptoms somatize and can lead to decreased immune function. This hypothesis has little or no in vivo evidence. The purpose of this study was to investigate evidence in the literature of a correlation between depression and infection with influenza.

Methodology: The databases PsycINFO, MEDLINE, IPA, and EMBASE were searched with search terms and keywords for "influenza" and "depression" or any derivation. Articles included in the search were required to be in English and conducted in human subjects.

Results: Our search identified 799 unique articles that related depression and influenza. After an abstract review, full article evaluation, and inclusion/exclusion criteria were applied, 10 articles remained. Of the 10 articles evaluated, 70% of the papers concluded no difference in hemagluttinin levels between depressed and non-depressed patients.

Conclusion: We believe this systematic review is the first to investigate the correlation of influenza infection and depression. Our search resulted in little scientific evidence and, therefore, the risk of influenza in patients with depression cannot be determined.