Correction to: Determinants of Influenza Mortality Trends: Age-Period-Cohort Analysis of Influenza Mortality in the United States, 1959-2016

First, we use Lexis surfaces based on Serfling models to highlight influenza mortality patterns as well as to identify lingering effects of early-life exposure to specific influenza virus subtypes (e.g., H1N1, H3N2).

Determinants of Influenza Mortality Trends: Age-Period-Cohort Analysis of Influenza Mortality in the United States, 1959-2016

This study examines the roles of age, period, and cohort in influenza mortality trends over the years 1959-2016 in the United States. First, we use Lexis surfaces based on Serfling models to highlight influenza mortality patterns as well as to identify lingering effects of early-life exposure to specific influenza virus subtypes (e.g., H1N1, H3N2). Second, we use age-period-cohort (APC) methods to explore APC linear trends and identify changes in the slope of these trends (contrasts). Our analyses reveal a series of breakpoints where the magnitude and direction of birth cohort trends significantly change, mostly corresponding to years in which important antigenic drifts or shifts took place (i.e., 1947, 1957, 1968, and 1978). Whereas child, youth, and adult influenza mortality appear to be influenced by a combination of cohort- and period-specific factors, reflecting the interaction between the antigenic experience of the population and the evolution of the influenza virus itself, mortality patterns of the elderly appear to be molded by broader cohort factors. The latter would reflect the processes of physiological capital improvement in successive birth cohorts through secular changes in early-life conditions. Antigenic imprinting, cohort morbidity phenotype, and other mechanisms that can generate the observed cohort effects, including the baby boom, are discussed.

The first wave of the 1918 influenza pandemic among soldiers of the Canadian expeditionary force

OBJECTIVES

This article evaluates the evidence for the presence of the first, mild wave of the 1918 influenza pandemic among soldiers in the Canadian Expeditionary Force (CEF).

METHODS

Death records for soldiers in the CEF who died in Canada in 1917 and 1918 were extracted from the Commonwealth War Graves Commission and record-linked to the Canada War Graves Registers, Circumstances of Casualty database. Monthly mortality rates from pneumonia and influenza (P&I) were compared with mortality rates from all other causes for 1917 and 1918, and by region for 1918.

RESULTS

The herald wave of influenza was present among CEF soldiers in 1918. P&I mortality was significantly higher in March and April 1918 than during the same period in 1917. P&I mortality rates varied across the country and were significantly higher among soldiers who died in the Maritime region of Canada. In March, Maritime P&I mortality was significantly higher than its counterpart in the West; in April it was significantly higher than P&I mortality in both the Central and Western regions.

CONCLUSIONS

The CEF findings suggest that local, geographic heterogeneity characterized the first wave of the 1918 influenza pandemic in Canada and illustrate the ways in which well-established, historical patterns of cross-border social contact with the United States, coupled with the special conditions created by warfare, disproportionately funnelled influenza into particular regions. Identification of the mild first wave among soldiers in the CEF calls for more research on the civilian experience of both waves of influenza in Canada.

Age-specific mortality during the 1918 influenza pandemic: unravelling the mystery of high young adult mortality

The worldwide spread of a novel influenza A (H1N1) virus in 2009 showed that influenza remains a significant health threat, even for individuals in the prime of life. This paper focuses on the unusually high young adult mortality observed during the Spanish flu pandemic of 1918. Using historical records from Canada and the U.S., we report a peak of mortality at the exact age of 28 during the pandemic and argue that this increased mortality resulted from an early life exposure to influenza during the previous Russian flu pandemic of 1889-90. We posit that in specific instances, development of immunological memory to an influenza virus strain in early life may lead to a dysregulated immune response to antigenically novel strains encountered in later life, thereby increasing the risk of death. Exposure during critical periods of development could also create holes in the T cell repertoire and impair fetal maturation in general, thereby increasing mortality from infectious diseases later in life. Knowledge of the age-pattern of susceptibility to mortality from influenza could improve crisis management during future influenza pandemics.

Lost in transition: influenza in the British army in the 1830s and 1840s

This paper uses surgeons' reports from the 1830s and 1840s to investigate routine regimental medical care by focusing on a familiar, non-fatal disease. The regimental reports are used to describe the classification of influenza and the use of antiphlogistic regimen to treat the disease. Also discussed is how the surgeons reconciled the rapid spread of influenza with the predominant causation beliefs of the time. Furthermore, the patterns of influenza morbidity in the early middle 19th century are discussed, adding to the understanding of the historical epidemiology of this genetically variable virus.

Social contexts, syndemics, and infectious disease in northern Aboriginal populations

Until the last half of the 20th century, infectious diseases dominated the health profile of northern North American Aboriginal communities. Research on the 1918 influenza pandemic exemplifies some of the ways in which the social context of European contact and ensuing economic developments affected the nature of infectious disease ecology as well as the frequency and severity of the problem. To understand these impacts it is necessary to consider the web of interactions among multiple pathogens, the biology of the human host, and the social environment in which people lived. At the very least, an understanding of the history of the impact of infectious diseases on northern North American communities requires attention not only to potential interactions among cocirculating pathogens, but their links to key social, historical, and economic factors that exacerbated their adverse effects and contributed to excess mortality.

Simulating the effect of quarantine on the spread of the 1918-19 flu in central Canada

Quarantine is often proposed and sometimes used to control the spread of infectious diseases through a human population. Yet there is usually little or no information on the effectiveness of attempting to quarantine humans that is not of an anecdotal or conjectural nature. This paper describes how a compartmental model for the geographic spread of infectious diseases can be used to address the potential effectiveness of human quarantine. The model is applied to data from the historical record in central Canada around the time of the 1918-19 influenza epidemic. Information on the daily mobility patterns of individuals engaged in the fur trade throughout the region prior to, during, and immediately after the epidemic are used to determine whether rates of travel were affected by informal quarantine policies imposed by community leaders. The model is then used to assess the impact of observed differences in travel on the spread of the epidemic. Results show that when mobility rates are very low, as in this region, quarantine practices must be highly effective before they alter disease patterns significantly. Simulation results suggest, though, that effectiveness varies depending on when the limitation on travel between communities is implemented and how long it lasts, and that a policy of introducing quarantine at the earliest possible time may not always lead to the greatest reduction in cases of a disease.

Modeling the influence of settlement structure on the spread of influenza among communities

Several factors play critical roles in the geographic spread of infectious diseases, including the movement of people between communities and the social and economic structure of groups of communities. A mathematical model has been developed to examine the individual and shared impact of these factors. This model was applied to the spread of the 1918-1919 influenza epidemic in three Aboriginal communities in central Canada. Previously published results from simulations of the model used parameter estimates for mobility patterns that were derived from historical documents from the study communities, especially Hudson's Bay Company post journals. We have termed this model the Frontier pattern. In this paper we extend that work to consider the consequences of three additional travel scenarios, which represent idealized trade and travel relationships between different communities. The three patterns include (a) the Central Marketplace scenario, an idealization of relations between a central community and its satellites in which a single central community satisfies all needs of the satellite communities; (b) the Sister Towns scenario, which allows travel among all communities and overemphasizes communication between satellites so that the ramifications of small town interactions are easier to observe; and (c) the Circuit scenario, which represents a hypothetical trade network that is a series of unidirectional dyad relationships linking all communities within a region. Results from simulations of the four mobility patterns are compared to assess the potential impact different social and economic relationships among communities may have had on the geographic spread of the 1918 influenza epidemic in central Canada and in other regions. These results reinforce conclusions that show that variation in patterns of mobility significantly influences the timing of epidemic peaks but only minimally alters the number of cases within a community. In addition, comparisons of the different models indicate that a central location in the social and political hierarchy of a region may be more important in influencing patterns of epidemic spread than just a central location with regard to travel patterns. Furthermore, who was actually travelling and where they were travelling had important consequences for epidemic spread. Am. J. Hum. Biol. 12:736-748, 2000. Copyright 2000 Wiley-Liss, Inc.

Investigating the weaning process in past populations

The 19th century St. Thomas'Anglican churchyard in Belleville, Ontario, Canada is associated with a large and well-preserved infant skeletal collection (n = 149) and good-quality parish records that document interments in the graveyard (1821-1874). By using a combination of historical demographic and stable nitrogen isotope analyses on the parish records and skeletal remains, respectively, a general pattern of extended nursing for about 14 months, introduction of foods other than breast milk by around 5 months of age, and variation in breast-feeding and weaning behaviours were detected for St. Thomas' infants. The results demonstrate that it is possible to go beyond the concept of weaning age to explore the weaning process in past populations when appropriate and large samples of documentary and skeletal data are available.

Structured epidemic models and the spread of influenza in the central Canadian subarctic

Patterns of transmission of infectious diseases within and among populations are strongly affected by population structure, which can either facilitate or limit interactions among people from different groups. Results from several theoretical studies show that nonrandom mixing among subgroups can affect the time when an infectious disease is introduced to the population, the speed of propagation of the disease, and the severity of an epidemic. Because many of these models focus on the effects of population structure, they are functionally similar to models used to describe the genetic structure of a population. One major difference between genetic models and epidemic models is that genetic models, with a time scale of the order of generations, incorporate migrations (or permanent movement) among subgroups, whereas epidemic models, with a time scale of the order of days or weeks, must incorporate short-term mobility among subgroups. Such mobility can be included in models for epidemic spread by explicitly incorporating the process by which residents from different locations interact with one another. We present a derivation of a mobility model for epidemic processes and apply it to the spread of the 1918-1919 influenza epidemic among the Cree and Métis people associated with three Hudson's Bay Company posts in the central Canadian Subarctic. The model distinguishes mobility from population effects. Results indicate that social organization (population effects) and social responses to the epidemic were more important than movement patterns (mobility) in explaining the differential impact of this virgin soil epidemic on the three study communities.

Changing patterns of mortality seasonality among the western James Bay Cree

Anglican Church of Canada burial records from 1851-1964 for the Moose Factory First Nation are analysed for mortality seasonality. The 113-year study period is subdivided into three death cohorts (1851-1906, 1914-1945 and 1946-1964) that broadly reflect the late 19th century, early 20th century, and the post-WWII periods, respectively. The data are partitioned into three age groups: infants (< 1), children (1-14), and adults (15+) to determine whether the hazards of death by season varied by age. The results show a clear and statistically significant pattern of seasonal mortality in the 19th century cohort for all three age groups, with a marked peak in mortality in the summer and a smaller peak in winter deaths (chi 2 = 84.82, df = 11, p < 0.001). By the early 20th century, the seasonal pattern disappears and the risks of death are consistent throughout the annual cycle (chi 2 = 16.5, df = 11, p = 0.124). It is argued that changes in the social and economic fabric of life, associated with the decline of the fur-trade, stimulated an epidemiologic transition among the Moose Factory Cree by the early 20th century, well in advance of WWII, the event normally used to mark both the onset of the phenomenon and improved health care delivery to the region.