Background: SARS-CoV-2 is straining health care systems globally. The burden on hospitals during the pandemic could be reduced by implementing prediction models that can discriminate patients who require hospitalization from those who do not. The COVID-19 vulnerability (C-19) index, a model that predicts which patients will be admitted to hospital for treatment of pneumonia or pneumonia proxies, has been developed and proposed as a valuable tool for decision-making during the pandemic. However, the model is at high risk of bias according to the "prediction model risk of bias assessment" criteria, and it has not been externally validated.

Objective: The aim of this study was to externally validate the C-19 index across a range of health care settings to determine how well it broadly predicts hospitalization due to pneumonia in COVID-19 cases.

Methods: We followed the Observational Health Data Sciences and Informatics (OHDSI) framework for external validation to assess the reliability of the C-19 index. We evaluated the model on two different target populations, 41,381 patients who presented with SARS-CoV-2 at an outpatient or emergency department visit and 9,429,285 patients who presented with influenza or related symptoms during an outpatient or emergency department visit, to predict their risk of hospitalization with pneumonia during the following 0-30 days. In total, we validated the model across a network of 14 databases spanning the United States, Europe, Australia, and Asia.

Results: The internal validation performance of the C-19 index had a C statistic of 0.73, and the calibration was not reported by the authors. When we externally validated it by transporting it to SARS-CoV-2 data, the model obtained C statistics of 0.36, 0.53 (0.473-0.584) and 0.56 (0.488-0.636) on Spanish, US, and South Korean data sets, respectively. The calibration was poor, with the model underestimating risk. When validated on 12 data sets containing influenza patients across the OHDSI network, the C statistics ranged between 0.40 and 0.68.

Conclusions: Our results show that the discriminative performance of the C-19 index model is low for influenza cohorts and even worse among patients with COVID-19 in the United States, Spain, and South Korea. These results suggest that C-19 should not be used to aid decision-making during the COVID-19 pandemic. Our findings highlight the importance of performing external validation across a range of settings, especially when a prediction model is being extrapolated to a different population. In the field of prediction, extensive validation is required to create appropriate trust in a model.


©Jenna M Reps, Chungsoo Kim, Ross D Williams, Aniek F Markus, Cynthia Yang, Talita Duarte-Salles, Thomas Falconer, Jitendra Jonnagaddala, Andrew Williams, Sergio Fernández-Bertolín, Scott L DuVall, Kristin Kostka, Gowtham Rao, Azza Shoaibi, Anna Ostropolets, Matthew E Spotnitz, Lin Zhang, Paula Casajust, Ewout W Steyerberg, Fredrik Nyberg, Benjamin Skov Kaas-Hansen, Young Hwa Choi, Daniel Morales, Siaw-Teng Liaw, Maria Tereza Fernandes Abrahão, Carlos Areia, Michael E Matheny, Kristine E Lynch, María Aragón, Rae Woong Park, George Hripcsak, Christian G Reich, Marc A Suchard, Seng Chan You, Patrick B Ryan, Daniel Prieto-Alhambra, Peter R Rijnbeek. Originally published in JMIR Medical Informatics (http://medinform.jmir.org), 05.04.2021. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR Medical Informatics, is properly cited. The complete bibliographic information, a link to the original publication on http://medinform.jmir.org/, as well as this copyright and license information must be included.

Cite as

Reps, J., Kim, C., Williams, R., Markus, A., Yang, C., Salles, T., Falconer, T., Jonnagaddala, J., Williams, A., Fernández-Bertolín, S., DuVall, S., Kostka, K., Rao, G., Shoaibi, A., Ostropolets, A., Spotnitz, M., Zhang, L., Casajust, P., Steyerberg, E., Nyberg, F., Kaas-Hansen, B., Choi, Y., Morales, D., Liaw, S., Abrahão, M., Areia, C., Matheny, M., Aragón, M., Park, R., Hripcsak, G., Reich, C., Suchard, M., You, S., Ryan, P., Prieto-Alhambra, D. & Rijnbeek, P. 2021, 'Implementation of the COVID-19 vulnerability index across an international network of health care data sets: Collaborative external validation study', JMIR Medical Informatics, 9(4), article no: e21547. https://doi.org/10.2196/21547

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Last updated: 16 June 2022
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