Impact of prior/concurrent exposure to infectious diseases on variability in the 1918-19 flu epidemic on Newfoundland [abstract]

Abstract only availableBetween 1918 and 1920 nearly 2000 people on the island of Newfoundland died from influenza, pneumonia, and related illnesses. Deaths were recorded from all parts of the island, but there is substantial regional variability in both timing and impact. One factor that may influence regional patterns of spread of an epidemic, but that is underappreciated, is the importance of prior and concurrent exposure to other infectious diseases. This paper discusses the possible impact on flu patterns of both exposure to a 1916 measles epidemic and its complications. Initial analysis of 1918-20 mortality suggested that widespread exposure to the 1916 measles epidemic may have reduced mortality during the flu epidemic, but further analyses failed to support the hypothesis. These analyses did indicate additional factors that may have obscured the ability to detect such an interaction, the most important of which were a significant difference in the size of the two epidemics and population size differences among communities. We describe here new studies focusing on these issues. This study highlights the importance of considering the co-circulation of multiple pathogens and potential interactions between acute and chronic conditions when trying to understand the impact of human infectious diseases.Government of Canada-Canada Studies Faculty Research Grant Program, University of Missouri McNair Scholars Program, MU Research Council, UM Research Board

Modeling and analyzing HIV transmission: the effect of contact patterns

A compartmental model is presented for the spread of HIV in a homosexual population divided into subgroups by degree of sexual activity. The model includes constant recruitment rates for the susceptibles in the subgroups. It incorporates the long infectious period of HIV-infected individuals and allows one to vary infectiousness over the infectious period. A new pattern of mixing, termed preferred mixing, is defined, in which a fraction of a group's contacts can be reserved for within-group contacts, the remainder being subject to proportional mixing. The fraction reserved may differ among groups. In addition, the classic definition of reproductive number is generalized to show that for heterogeneous populations in general the endemic threshold is [beta]DcY, where cY is the mean number of contacts per infective. The most important finding is that the pattern of contacts between the different groups has a major effect on the spread of HIV, an effect inadequately recognized or studied heretofore.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27021/1/0000009.pd

Population Structure and the Spread of Disease

A model for the spread of disease in a population consisting of several interacting subpopulations is developed and analyzed. The model considers two different types of interactions between individuals; interac- tions between individuals within a subpopulation because of geographic proximity, and interactions between individuals of the same or different subpopulations because of attendance at common social functions. A sta­bility analysis is performed on the equilibria of the model, which shows that there are two possible stable states. One stable state consists of a population composed solely of susceptible individuals with no disease present. The second stable state occurs at an interior point where there are susceptible, infective, and recovered individuals present at all times. The condition for maintenance (or extinction) of the disease is found to be given by a simple inequality relating the removal rate of infectives to the infection rate of susceptibles.Three idealized patterns of social interaction are studied. These in­clude completely random mixing, complete isolation of all groups, and local clustering of some of the groups with others randomly mixing. In addition, results are discussed in relation to a particular type of social interaction, attendance of preschool children at day care centers. The analysis shows that the threshold for disease maintenance is more easily exceeded in cen­ters that are members of a small local cluster than in randomly mixing centers, but that the spread of the disease throughout the population occurs more rapidly when the initial case attends a randomly mixing center. These analytical results are compared with data on the spread of hepatitis A among pre-school children in Albuquerque, New Mexico

“We didn't get much schooling because we were fishing all the time”: Potential impacts of irregular school attendance on the spread of epidemics

Objectives: Especially in traditional, rural, and low-income areas, children attend school irregularly. School-based interventions are common mitigation strategies for infectious disease epidemics, but if daily attendance is not the norm, the impact of schools on disease spread might be overestimated. Methods: We use an agent-based model of an early 20th century Newfound- land community to compare epidemic size and duration in three scenarios: (1) all school-aged children attend school each weekday, (2) students aged 10–15 have a chance of engaging in adult activities each day, and (3) students aged 10–15 have a chance of being reassigned to adult roles at the start of each simulation and thus never attend school. Results: As the probability of not attending school increases, epidemics become smaller and peak earlier. The change in final size is larger with perma- nent reassignment (35% at baseline, 18% at maximum reassignment) than with daily nonattendance (35% vs. 22%). For both scenarios, the peak occurs 3 days earlier with maximum absence compared to the baseline. Benefits extend beyond the reassigned agents, as all school-aged agents are more likely to escape infection with increasing reassignment, and on average, 3–6 additional agents (2.6%–5.3%) escape infection compared to the baseline. Conclusions: This study demonstrates that absenteeism can have important impacts on epidemic outcomes. Thus, socioeconomic and other reasons for nonattendance of school, as well as how rates vary in different contexts, must be considered in models predicting epidemic outcomes or evaluating public health interventions in the face of major pandemics

Geographic Spread of Measles on the Island of Dominica, West Indies

Because of the short incubation period of most acute infectious diseases, short-term and daily mobility are more important than permanent and seasonal migration for the spread of these diseases. Yet most studies of population mobility focus on permanent or semipermanent change of residence. Here, we describe the results from a field study conducted on the island of Dominica, West Indies, during the summers of 1989 and 1990 and the winter of 1991. The study was designed to collect data on short-term mobility rather than migration. These mobility data are linked with data on the patterns of measles transmission during a 1984 epidemic. Three-hundred five individuals from all parts of the island were interviewed about their daily travel patterns, their travel off the island, and the travel of members of their immediate family. In addition to these respondents, interviews were conducted with representatives of most of the major occupations that involve travel in the course of a workday. Data were also collected on the number and type of motor vehicles traveling along various routes on the island and on travel of native residents to the capital city, Roseau, to buy or sell at the major weekly market. Analysis of the interviews shows that travel within the island is clearly nonrandom. For example, almost everyone interviewed traveled to Roseau at least once a month, but 40% of the respondents had never been to any of the major villages in the Grand Bay Health District, which is only about a half-hour from Roseau. Patterns of disease transmission have been directly affected by these mobility patterns. The measles epidemic in 1984 apparently did not reach the Grand Bay Health District, even though all other areas of the island experienced significant rates of infection. Analysis of reasons for the relative isolation of the Grand Bay Health District indicates the importance of transportation patterns, as well as social, cultural, and geographic factors, to the disease transmission patterns throughout the island

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 Metis 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 o f this virgin soil epidemic on the three study communities

Applications of Agent-Based Modelling Techniques to Studies of Historical Epidemics: The 1918 Flu in Newfoundland and Labrador

The purpose of this article is twofold. First, the study addresses questions related to the spread and impact of the 1918 influenza pandemic in a small Newfoundland community, focusing on the role of large social institutions including an orphanage, school, and churches. Records indicate, for example, that residents of the orphanage in St. Anthony, our study community, experienced an increased risk of infection at different times during the epidemic than did members of the general community. Further, archival sources show that a variety of public health measures including closure of public gathering spaces were implemented throughout Newfoundland, but evidence suggests that the success of these measures varied. Second, this paper presents an argument for the important role computer simulation models can play in historical research, which is demonstrated using results from simulations focusing on social, demographic, and cultural factors, including behaviours and interactions of community residents. These examples highlight how modelling techniques can be used in historical research to address gaps in archival sources and help direct future research paths, and to test counterfactual scenarios to identify important factors influencing observed outcomes.L’objectif du présent article est double. D’une part, il traite de questions liées à la propagation et à l’incidence de la pandémie de grippe de 1918 dans une petite collectivité de Terre-Neuve. Il s’attarde au rôle des grandes institutions sociales, y compris l’orphelinat, l’école et les églises. Des sources indiquent, par exemple, que les résidents de l’orphelinat de St. Anthony, agglomération à l’étude, ont été exposés à des risques plus grands que les membres de la collectivité en général à divers moments de l’épidémie. Qui plus est, les archives révèlent que différentes mesures de santé publique, y compris la fermeture des lieux de rassemblement, ont été mises en oeuvre dans tout Terre-Neuve, mais des données suggèrent que ces mesures n’ont pas connu le même succès partout. D’autre part, l’article soutient l’importance des modèles de simulation informatisés pour la recherche en histoire. Pour ce faire, il utilise les résultats de simulations articulées autour de facteurs sociaux, démographiques et culturels, y compris le comportement des résidents de la collectivité et leurs interactions. Ces exemples mettent en lumière comment les techniques de modélisation servent à la recherche en histoire pour combler les lacunes des sources archivistiques et orienter les recherches futures ainsi que pour tester des scénarios contrefactuels afin de dégager des facteurs importants qui agissent sur les résultats observés

Environmental Context, Social Interactions, and the Spread of HIV

This issue was undated. The date given is an estimate.51 pages, 1 article*Environmental Context, Social Interactions, and the Spread of HIV* (Sattenspiel, Lisa; Castillo-Chavez, Carlos) 51 page