Interactions arising from sequential viral and bacterial infections may play important roles in the epidemiological outcome of many respiratory pathogens. Influenza virus has been implicated in the pathogenesis of several respiratory bacterial pathogens commonly associated with pneumonia. However, studies focusing on different scales of resolution have painted an inconsistent picture. Individual-scale animal experiments have unequivocally demonstrated an association, whereas the support in population-level epidemiological studies remains variable and unclear. We use multiple sources of epidemiological data which vary in the time periods they cover and the scales at which they are collected, and a mechanistic transmission model, both within a likelihood-based inference framework to characterize the nature, timing, and magnitude of this interaction. We find support for a strong but short-lived interaction, with influenza infection increasing susceptibility to pneumococcal (and other bacterial) pneumonia by ~100-fold, in line with our understanding from animal challenge experiments. The population-level impact of such an interaction can be modest during non-pandemic seasonal influenza periods (which may in turn make it difficult to detect), but can be substantially larger during pandemic periods (and also more detectable). We argue that these seemingly inconsistent observations at different scales can be explained by this proposed interaction: a strong but short-lived susceptibility enhancement of pneumonia following influenza.
Sourya Shresthra of the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health will present a noon seminar entitled "Characterizing the Role of Influenza in the Epidemiology of Pneumonia."