|The long-term impact of historical influenza pandemics on mental health 1872-1930|
Previous research has studied whether influenza infection may have long-term effects. Studies have linked long-term effects of pandemics to indicators of mental health, intelligence, functional limitations, socioeconomic status, and mortality. Despite clear impact of the Russian Influenza of 1889-90 and Spanish influenza of 1918-20 on mental health, as indicated by a large body of anecdotes from contemporary observers, there are very few empirical studies on the long-term historical association between influenza and mental health. Here, a flow-chart model showing the effects the two pandemics had on mental health is first given. Second, annual correlates of first-time asylum hospitalizations of individuals with mental disease linked to influenza and the corresponding influenza mortality in the non-institutionalized Norwegian population 1872-1929 will be analyzed.
Results shows that the number of first time hospitalized patients with mental diseases caused by influenza, compared to normal situations (respectively 1872-1889 and 1901-1917), increased by a an average annual factor of 2.6 in the 5 years following the Russian influenza 1890-1894 in 1889 and by an average annual factor of 7.2 in the 6 years following the Spanish influenza 1918-1924. The analysis cannot determine the part played by social isolation, individual pain and depression of illness from influenza, fear and discomfort, or the interactions of these factors, in explaining the excess hospitalizations. However, the analysis also shows that inter-pandemic seasonal influenza has an effect on the hospitalization rates, although much smaller compared to pandemics. The mental-health effect of seasonal influenza should mainly be a product of individual experience of influenza illness.