Testing the influenza-tuberculosis selective mortality hypothesis with Union Army data

Abstract

Using Cox regression, this paper shows a weak association between having tuberculosis and dying from influenza among Union Army veterans in late nineteenth-century America. It has been suggested elsewhere [Noymer, A. and M. Garenne (2000). The 1918 influenza epidemic's effects on sex differentials in mortality in the United States. Population and Development Review 26(3), 565-581.] that the 1918 influenza pandemic accelerated the decline of tuberculosis, by killing many people with tuberculosis. The question remains whether individuals with tuberculosis were at greater risk of influenza death, or if the 1918/post-1918 phenomenon arose from the sheer number of deaths in the influenza pandemic. The present findings, from microdata, cautiously point toward an explanation of Noymer and Garenne's selection effect in terms of age-overlap of the 1918 pandemic mortality and tuberculosis morbidity, a phenomenon I term "passive selection". Another way to think of this is selection at the cohort, as opposed to individual, level.

Fig. 1

Age mortality profile, influenza and pneumonia, 1917 and 1918, United States death registration area. Data from U.S. Department of Health, Education, and Welfare (1956).

Fig. 2

Age-standardized death rate, tuberculosis, 1900–1940, United States death registration area. Source: U.S. Department of Health, Education, and Welfare (1956).

Fig. 3

Smoothed hazard graph from model 6 (Table 4). The solid curve represents the hazard of influenza death among the tuberculous, and the dashed curve among the non-tuberculous. See text for discussion.