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  1. Article ; Online: Comparison of machine learning methods for estimating case fatality ratios: An Ebola outbreak simulation study.

    Forna, Alpha / Dorigatti, Ilaria / Nouvellet, Pierre / Donnelly, Christl A

    PloS one

    2021  Volume 16, Issue 9, Page(s) e0257005

    Abstract: Background: Machine learning (ML) algorithms are now increasingly used in infectious disease epidemiology. Epidemiologists should understand how ML algorithms behave within the context of outbreak data where missingness of data is almost ubiquitous.: ... ...

    Abstract Background: Machine learning (ML) algorithms are now increasingly used in infectious disease epidemiology. Epidemiologists should understand how ML algorithms behave within the context of outbreak data where missingness of data is almost ubiquitous.
    Methods: Using simulated data, we use a ML algorithmic framework to evaluate data imputation performance and the resulting case fatality ratio (CFR) estimates, focusing on the scale and type of data missingness (i.e., missing completely at random-MCAR, missing at random-MAR, or missing not at random-MNAR).
    Results: Across ML methods, dataset sizes and proportions of training data used, the area under the receiver operating characteristic curve decreased by 7% (median, range: 1%-16%) when missingness was increased from 10% to 40%. Overall reduction in CFR bias for MAR across methods, proportion of missingness, outbreak size and proportion of training data was 0.5% (median, range: 0%-11%).
    Conclusion: ML methods could reduce bias and increase the precision in CFR estimates at low levels of missingness. However, no method is robust to high percentages of missingness. Thus, a datacentric approach is recommended in outbreak settings-patient survival outcome data should be prioritised for collection and random-sample follow-ups should be implemented to ascertain missing outcomes.
    MeSH term(s) Computer Simulation ; Data Interpretation, Statistical ; Datasets as Topic ; Disease Outbreaks ; Hemorrhagic Fever, Ebola/epidemiology ; Hemorrhagic Fever, Ebola/mortality ; Humans ; Machine Learning ; Models, Statistical ; Research Design ; Survival Analysis
    Language English
    Publishing date 2021-09-15
    Publishing country United States
    Document type Comparative Study ; Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2267670-3
    ISSN 1932-6203 ; 1932-6203
    ISSN (online) 1932-6203
    ISSN 1932-6203
    DOI 10.1371/journal.pone.0257005
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Spatiotemporal variability in case fatality ratios for the 2013-2016 Ebola epidemic in West Africa.

    Forna, Alpha / Dorigatti, Ilaria / Nouvellet, Pierre / Donnelly, Christl A

    International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases

    2020  Volume 93, Page(s) 48–55

    Abstract: Background: For the 2013-2016 Ebola epidemic in West Africa, the largest Ebola virus disease (EVD) epidemic to date, we aim to analyse the patient mix in detail to characterise key sources of spatiotemporal heterogeneity in the case fatality ratios (CFR) ...

    Abstract Background: For the 2013-2016 Ebola epidemic in West Africa, the largest Ebola virus disease (EVD) epidemic to date, we aim to analyse the patient mix in detail to characterise key sources of spatiotemporal heterogeneity in the case fatality ratios (CFR).
    Methods: We applied a non-parametric Boosted Regression Trees (BRT) imputation approach for patients with missing survival outcomes and adjusted for model imperfection. Semivariogram analysis and kriging were used to investigate spatiotemporal heterogeneities.
    Results: CFR estimates varied significantly between districts and over time over the course of the epidemic. BRT modelling accounted for most of the spatiotemporal variation and interactions in CFR, but moderate spatial autocorrelation remained for distances up to approximately 90 km. Combining district-level CFR estimates and kriged district-level residuals provided the best linear unbiased predicted map of CFR accounting for the both explained and unexplained spatial variation. Temporal autocorrelation was not observed in the district-level residuals from the BRT estimates.
    Conclusions: This study provides new insight into the epidemiology of the 2013-2016 West African Ebola epidemic with a view of informing future public health contingency planning, resource allocation and impact assessment. The analytical framework developed in this analysis, coupled with key domain knowledge, could be deployed in real time to support the response to ongoing and future outbreaks.
    MeSH term(s) Africa, Western/epidemiology ; Epidemics ; Hemorrhagic Fever, Ebola/epidemiology ; Hemorrhagic Fever, Ebola/mortality ; Humans ; Spatial Analysis
    Language English
    Publishing date 2020-01-28
    Publishing country Canada
    Document type Journal Article
    ZDB-ID 1331197-9
    ISSN 1878-3511 ; 1201-9712
    ISSN (online) 1878-3511
    ISSN 1201-9712
    DOI 10.1016/j.ijid.2020.01.046
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Case Fatality Ratio Estimates for the 2013-2016 West African Ebola Epidemic: Application of Boosted Regression Trees for Imputation.

    Forna, Alpha / Nouvellet, Pierre / Dorigatti, Ilaria / Donnelly, Christl A

    Clinical infectious diseases : an official publication of the Infectious Diseases Society of America

    2019  Volume 70, Issue 12, Page(s) 2476–2483

    Abstract: Background: The 2013-2016 West African Ebola epidemic has been the largest to date with >11 000 deaths in the affected countries. The data collected have provided more insight into the case fatality ratio (CFR) and how it varies with age and other ... ...

    Abstract Background: The 2013-2016 West African Ebola epidemic has been the largest to date with >11 000 deaths in the affected countries. The data collected have provided more insight into the case fatality ratio (CFR) and how it varies with age and other characteristics. However, the accuracy and precision of the naive CFR remain limited because 44% of survival outcomes were unreported.
    Methods: Using a boosted regression tree model, we imputed survival outcomes (ie, survival or death) when unreported, corrected for model imperfection to estimate the CFR without imputation, with imputation, and adjusted with imputation. The method allowed us to further identify and explore relevant clinical and demographic predictors of the CFR.
    Results: The out-of-sample performance (95% confidence interval [CI]) of our model was good: sensitivity, 69.7% (52.5-75.6%); specificity, 69.8% (54.1-75.6%); percentage correctly classified, 69.9% (53.7-75.5%); and area under the receiver operating characteristic curve, 76.0% (56.8-82.1%). The adjusted CFR estimates (95% CI) for the 2013-2016 West African epidemic were 82.8% (45.6-85.6%) overall and 89.1% (40.8-91.6%), 65.6% (61.3-69.6%), and 79.2% (45.4-84.1%) for Sierra Leone, Guinea, and Liberia, respectively. We found that district, hospitalisation status, age, case classification, and quarter (date of case reporting aggregated at three-month intervals) explained 93.6% of the variance in the naive CFR.
    Conclusions: The adjusted CFR estimates improved the naive CFR estimates obtained without imputation and were more representative. Used in conjunction with other resources, adjusted estimates will inform public health contingency planning for future Ebola epidemics, and help better allocate resources and evaluate the effectiveness of future inventions.
    MeSH term(s) Epidemics ; Guinea ; Hemorrhagic Fever, Ebola/epidemiology ; Humans ; Liberia/epidemiology ; Sierra Leone
    Language English
    Publishing date 2019-08-06
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1099781-7
    ISSN 1537-6591 ; 1058-4838
    ISSN (online) 1537-6591
    ISSN 1058-4838
    DOI 10.1093/cid/ciz678
    Database MEDical Literature Analysis and Retrieval System OnLINE

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