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159. The ecological effects of individual exposures and nonlinear disease dynamics in populations

Author

Koopman, J S and Longini, I M

Subjects
Research Article
Abstract

To describe causally predictive relationships, model parameters and the data used to estimate them must correspond to the social context of causal actions. Causes may act directly upon the individual, during a contact between individuals, or upon a group dynamic. Assuming that outcomes in different individuals are independent puts the causal action directly upon individuals. Analyses making this assumption are thus inappropriate for infectious diseases, for which risk factors alter the outcome of contacts between individuals. Transmission during contact generates nonlinear infection dynamics. These dynamics can so attenuate exposure-infection relationships at the individual level that even risk factors causing the vast majority of infections can be missed by individual-level analyses. On the other hand, these dynamics amplify causal associations between exposure and infection at the ecological level. The amplification and attenuation derive from chains of transmission initiated by exposed individuals but involving unexposed individuals. A study of household exposure to the only vector of dengue in Mexico illustrates the phenomenon. An individual-level analysis demonstrated almost no association between exposure and infection. Ecological analysis, in contrast, demonstrated a strong association. Transmission models that are devoid of any sources of the ecological fallacy are used to illustrate how nonlinear dynamics generate such results.

Published
1994

175. Transmission Model Analysis of Nontypeable Haemophilus Influenzae.

Author

Hillier, Frederick S., Brandeau, Margaret L., Sainfort, François, Pierskalla, William P., Koopman, James S., Lin, Ximin, Chick, Stephen E., and Gilsdorf, Janet R.

Abstract

The effects of immunity stimulated by natural colonization with Nontypeable Haemophilus influenzae (NTHi) were assessed using population models of transmission and data from the literature on NTHi colonization prevalence by age, NTHi acute otitis media (AOM) incidence by age, NTHi antibody levels, and colonization duration. The models allowed both contact patterns and immunity to influence colonization and disease patterns by age. To fit the data, the models required colonization to stimulate immunity affecting both transmission (susceptibility and contagiousness) and pathogenicity (AOM given colonization). Model analysis demonstrated that immunity affecting transmission influenced AOM incidence in the first year of life from 4.6 to 39.5 times as much as immunity reducing pathogenicity. This differential decreased with age until age three and then rose again. It was important, however, across all age groups. The conclusion that immunity affecting transmission had larger effects on AOM incidence than immunity affecting pathogenicity was robust to model form and to reasonable variation in the data. Because sensitivity to NTHi strain interactions and age patterns of infection by strain could not be assessed and because data on the distribution of NTHi strains across all ages are deficient, this conclusion must still be viewed as tentative. Nonetheless, these results make it imperative that trials of potential NTHi vaccines be designed to insure accurate assessment of effects on transmission. The models presented here provide the basis for the construction of discrete individual simulation models for use in designing the most informative and powerful vaccine trials. [ABSTRACT FROM AUTHOR]

Published
2005
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176. Microbial Risk Assessment for Drinking Water.

Author

Hillier, Frederick S., Brandeau, Margaret L., Sainfort, François, Pierskalla, William P., Chick, Stephen E., Soorapanth, Sada, and Koopman, James S.

Abstract

Infectious microbes can be transmitted through the drinking water supply. Recent research indicates that infection transmission dynamics influence the public health benefit of water treatment interventions, although some risk assessments currently in use do not fully account for those dynamics. This chapter models the public health benefit of two interventions: improvements to centralized water treatment facilities, and localized point-of-use treatments in the homes of particularly susceptible individuals. A sensitivity analysis indicates that the best option is not as obvious as that suggested by an analysis that ignores infection dynamics suggests. Deterministic and stochastic dynamic systems models prove to be useful tools for assessing the dynamics of risk exposure. [ABSTRACT FROM AUTHOR]

Published
2005
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177. CHAPTER 7: MASS-ACTION AND SYSTEM ANALYSIS OF INFECTION TRANSMISSION.

Author

Koopman, James S.

Abstract

Chapter 7 of the book "Ecological Paradigms Lost: Routes of Theory Change" is presented. It examines the mass-action paradigm for epidemiology in the context of theory change advancing a science than can analyze population in more detailed and informative ways. It outlines ways in which the directions that theory change can take are determined by the model forms used to analyze infection transmission through populations. It relates the requirements for assessing the robustness of model assumptions.

Published
2005

178. TRANSMISSION MODEL ANALYSIS OF NONTYPEABLE HAEMOPHILUS INFLUENZAE.

Author

Koopman, James S., Ximin Lin, Chick, Stephen E., and Gilsdorf, Janet R.

Subjects
IMMUNITY, HAEMOPHILUS diseases, INFECTION, VACCINES, BACTERIA, INFECTIOUS disease transmission
Abstract

The effects of immunity stimulated by natural colonization with Nontypeable Haemophilus influenzae (NTHi) were assessed using population models of transmission and data from the literature on NTHi colonization prevalence by age, NTHi acute otitis media (AOM) incidence by age, NTHi antibody levels, and colonization duration. The models allowed both contact patterns and immunity to influence colonization and disease patterns by age. To fit the data, the models required colonization to stimulate immunity affecting both transmission (susceptibility and contagiousness) and pathogenicity (AOM given colonization). Model analysis demonstrated that immunity affecting transmission influenced AOM incidence in the first year of life from 4.6 to 39.5 times as much as immunity reducing pathogenicity. This differential decreased with age until age three and then rose again. It was important, however, across all age groups. The conclusion that immunity affecting transmission had larger effects on AOM incidence than immunity affecting pathogenicity was robust to model form and to reasonable variation in the data. Because sensitivity to NTHi strain interactions and age patterns of infection by strain could not be assessed and because data on the distribution of NTHi strains across all ages are deficient, this conclusion must still be viewed as tentative. Nonetheless, these results make it imperative that trials of potential NTHi vaccines be designed to insure accurate assessment of effects on transmission. The models presented here provide the basis for the construction of discrete individual simulation models for use in designing the most informative and powerful vaccine trials. [ABSTRACT FROM AUTHOR]

Published
2004

179. MICROBIAL RISK ASSESSMENT FOR DRINKING WATER.

Author

Chick, Stephen E., Soorapanth, Sada, and Koopman, James S.

Subjects
BACTERIA, RISK assessment, DRINKING water, SEWAGE purification, ORNSTEIN-Uhlenbeck process, INFECTION
Abstract

Infectious microbes can be transmitted through the drinking water supply. Recent research indicates that infection transmission dynamics influence the public health benefit of water treatment interventions, although some risk assessments currently in use do not fully account for those dynamics. This chapter models the public health benefit of two interventions: improvements to centralized water treatment facilities, and localized point-of-use treatments in the homes of particularly susceptible individuals. A sensitivity analysis indicates that the best option is not as obvious as that suggested by an analysis that ignores infection dynamics suggests. Deterministic and stochastic dynamic systems models prove to be useful tools for assessing the dynamics of risk exposure. [ABSTRACT FROM AUTHOR]

Published
2004

185. Determining the Anaerobic Threshold in Postpolio Syndrome: Comparison With Current Guidelines for Training Intensity Prescription.

Author

Voorn, Eric L., Gerrits, Karin H., Koopman, Fieke S., Nollet, Frans, and Beelen, Anita

Abstract

Abstract: Objectives: To determine whether the anaerobic threshold (AT) can be identified in individuals with postpolio syndrome (PPS) using submaximal incremental exercise testing, and to compare current guidelines for intensity prescription in PPS with the AT. Design: Cohort study. Setting: Research laboratory. Participants: Individuals with PPS (N=82). Interventions: Not applicable. Main Outcome Measures: Power output, gas exchange variables, heart rate, and rating of perceived exertion (RPE) were measured in an incremental submaximal cycle ergometry test. Two independent observers identified the AT. Comparison of current guidelines for training intensity prescription in PPS (40%–60% heart rate reserve [HRR] or RPE of 12) with the AT was based on correlations between recommended heart rate and the heart rate at the AT. In addition, we determined the proportion of individuals that would have been recommended to train at an intensity corresponding to their AT. Results: The AT was identified in 63 (77%) of the participants. Pearson correlation coefficients between the recommended heart rate and the heart rate at the AT were lower in cases of 40% HRR (r=.56) and 60% HRR (r=.50) than in cases of prescription based on the RPE (r=.86). Based on the RPE, 55% of the individuals would have been recommended to train at an intensity corresponding to their AT. This proportion was higher compared with 40% HRR (41%) or 60% HRR (18%) as criterion. Conclusions: The AT can be identified in most individuals with PPS offering an individualized target for aerobic training. If the AT cannot be identified (eg, because gas analysis equipment is not available), intensity prescription can best be based on the RPE. [Copyright &y& Elsevier]

Published
2014
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186. GERMS

Author

Adams, Andrew L., primary, Koopman, James S., additional, Chick, Stephen E., additional, and Yu, Peter J., additional

Published
1999
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192. Authors?? Reply

Author

Jacquez, John A., primary, Koopman, James S., additional, Simon, Carl P., additional, and Longini, Ira M., additional

Published
1995
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195. The dynamics of methicillin-resistant Staphylococcus aureus exposure in a hospital model and the potential for environmental intervention.

Author

Plipat, Nottasorn, Spicknall, Ian H., Koopman, James S., and Eisenberg, Joseph N. S.

Subjects
INFECTION prevention, STAPHYLOCOCCUS aureus, METHICILLIN resistance, HYGIENE, CLEANING, MEDICAL personnel
Abstract

Background Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of healthcareassociated infections. An important control strategy is hand hygiene; however, noncompliance has been a major problem in healthcare settings. Furthermore, modeling studies have suggested that the law of diminishing return applies to hand hygiene. Other additional control strategies such as environmental cleaning may be warranted, given that MRSApositive individuals constantly shed contaminated desquamated skin particles to the environment. Methods We constructed and analyzed a deterministic environmental compartmental model of MRSA fate, transport, and exposure between two hypothetical hospital rooms: one with a colonized patient, shedding MRSA; another with an uncolonized patient, susceptible to exposure. Healthcare workers (HCWs), acting solely as vectors, spread MRSA from one patient room to the other. Results Although porous surfaces became highly contaminated, their low transfer efficiency limited the exposure dose to HCWs and the uncolonized patient. Conversely, the high transfer efficiency of nonporous surfaces allows greater MRSA transfer when touched. In the colonized patient's room, HCW exposure occurred more predominantly through the indirect (patient to surfaces to HCW) mode compared to the direct (patient to HCW) mode. In contrast, in the uncolonized patient's room, patient exposure was more predominant in the direct (HCW to patient) mode compared to the indirect (HCW to surfaces to patient) mode. Surface wiping decreased MRSA exposure to the uncolonized patient more than daily surface decontamination. This was because wiping allowed higher cleaning frequency and cleaned more total surface area per day. Conclusions Environmental cleaning should be considered as an integral component of MRSA infection control in hospitals. Given the previously under-appreciated role of surface contamination in MRSA transmission, this intervention mode can contribute to an effective multiple barrier approach in concert with hand hygiene. [ABSTRACT FROM AUTHOR]

Published
2013
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196. Model Analysis of Fomite Mediated Influenza Transmission.

Author

Jijun Zhao, Eisenberg, Joseph E., Spicknall, Ian H., Li, Sheng, and Koopman, James S.

Subjects
INFLUENZA, PATHOGENIC microorganisms, MICROORGANISMS, COMMUNICABLE diseases, RESPIRATORY infections, VIRUS diseases
Abstract

Fomites involved in influenza transmission are either hand- or droplet-contaminated. We evaluated the interactions of fomite characteristics and human behaviors affecting these routes using an Environmental Infection Transmission System (EITS) model by comparing the basic reproduction numbers (R0) for different fomite mediated transmission pathways. Fomites classified as large versus small surface sizes (reflecting high versus low droplet contamination levels) and high versus low touching frequency have important differences. For example, 1) the highly touched large surface fomite (public tables) has the highest transmission potential and generally strongest control measure effects; 2) transmission from dropletcontaminated routes exceed those from hand-contaminated routes except for highly touched small surface fomites such as door knob handles; and 3) covering a cough using the upper arm or using tissues effectively removes virus from the system and thus decreases total fomite transmission. Because covering a cough by hands diverts pathogens from the dropletfomite route to the hand-fomite route, this has the potential to increase total fomite transmission for highly touched small surface fomites. An improved understanding and more refined data related to fomite mediated transmission routes will help inform intervention strategies for influenza and other pathogens that are mediated through the environment. [ABSTRACT FROM AUTHOR]

Published
2012
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