{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,7]],"date-time":"2026-08-07T17:24:36Z","timestamp":1786123476426,"version":"build-2736575974"},"reference-count":28,"publisher":"American Medical Association (AMA)","issue":"6","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JAMA Netw Open"],"abstract":"\n Importance<\/jats:title>\n There were well-documented changes in health care use during the COVID-19 pandemic. Little is known about whether there were any associated decreases in claims-based comorbidity ascertainment that might have relevance to health services and policy research.<\/jats:p>\n <\/jats:sec>\n \n Objective<\/jats:title>\n To quantify differences in claims-based comorbidity assessment in Medicare beneficiaries pre\u2013 vs post\u2013COVID-19.<\/jats:p>\n <\/jats:sec>\n \n Design, Setting, and Participants<\/jats:title>\n This cross-sectional study analyzed data from the 30 Chronic Conditions Warehouse 1- or 2-year lookback claims algorithms to ascertain each comorbidity with exact date ranges for all fee-for-service (FFS) and Medicare Advantage (MA) beneficiaries. Data were analyzed from April 2025 to April 2026.<\/jats:p>\n <\/jats:sec>\n \n Exposures<\/jats:title>\n The first quarter (Q1) of 2019 and 2022 were evaluated as pre\u2013 and post\u2013COVID-19, respectively.<\/jats:p>\n <\/jats:sec>\n \n Main Outcomes and Measures<\/jats:title>\n The main outcomes were comorbidities per beneficiary and association between each comorbidity and mortality in 2019 vs 2022. The changes in prevalence of each comorbidity between 2019 and 2022 were analyzed and fit models within disjoint population subgroups were combined via multilevel meta-analysis models to determine whether each comorbidity\u2019s association with mortality changed over time.<\/jats:p>\n <\/jats:sec>\n \n Results<\/jats:title>\n This study included 59\u202f514\u202f042 beneficiaries in 2019 (32\u202f351\u202f732 females [54.4%]; 50\u202f814\u202f834 aged 65 years or older [85.4%]) and 63\u202f202\u202f599 beneficiaries in 2022 (34\u202f377\u202f560 females [54.4%]; 55\u202f197\u202f435 aged 65 years or older [87.3%]). The mean number of coded comorbidities per beneficiary decreased from 3.85 to 3.62 for FFS and 4.54 to 4.39 for MA (\u22120.15) between 2019 and 2022. In FFS, 19 comorbidities (63.3%) decreased, 2 (6.7%) were unchanged, and 9 (30%) increased. In MA, 14 comorbidities (46.7%) decreased, 7 (23.3%) were unchanged, and 9 (30%) increased. In multivariable analyses pooled across FFS and MA, 11 comorbidities (36.7%) were more positively associated with mortality, and 4 (13.3%) were more negatively associated with mortality in Q1 2022 than in Q1 2019.<\/jats:p>\n <\/jats:sec>\n \n Conclusions and Relevance<\/jats:title>\n Coded levels of many comorbidities in Medicare were lower postpandemic than prepandemic, and the association of these codes with mortality changed. This suggests that across the COVID-19 pandemic comorbidity capture was affected by utilization changes, and the association between comorbidities and mortality changed as a result. Analyses that include immediately pre\u2013 or post\u2013COVID-19 data and condition inferences on membership in utilization-based disease groups, or use claims-based risk adjustment, may be subject to bias.<\/jats:p>\n <\/jats:sec>","DOI":"10.1001\/jamanetworkopen.2026.17766","type":"journal-article","created":{"date-parts":[[2026,6,12]],"date-time":"2026-06-12T15:30:18Z","timestamp":1781278218000},"page":"e2617766","source":"Crossref","is-referenced-by-count":1,"title":["Chronic Conditions and Mortality in Medicare Beneficiaries Before and After the COVID-19 Pandemic"],"prefix":"10.1001","volume":"9","author":[{"given":"R. J.","family":"Waken","sequence":"first","affiliation":[{"name":"Division of Biostatistics, Institute for Informatics, Data Science, and Biostatistics, Washington University School of Medicine, St Louis, Missouri"},{"name":"Center for Advancing Health Services, Policy & Economics Research, Washington University, St Louis, Missouri"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Fengxian","family":"Wang","sequence":"additional","affiliation":[{"name":"Center for Advancing Health Services, Policy & Economics Research, Washington University, St Louis, Missouri"},{"name":"Cardiology Division, Department of Medicine, Washington University School of Medicine, St Louis, Missouri"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jose F.","family":"Figueroa","sequence":"additional","affiliation":[{"name":"Department of Health Policy and Management, Harvard T.H. Chan School of Public Health, Boston, Massachusetts"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rishi K.","family":"Wadhera","sequence":"additional","affiliation":[{"name":"Richard A. and Susan F. Smith Center for Outcomes Research, Boston, Massachusetts"},{"name":"Division of Cardiovascular Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Khavya","family":"Avula","sequence":"additional","affiliation":[{"name":"Center for Advancing Health Services, Policy & Economics Research, Washington University, St Louis, Missouri"},{"name":"Cardiology Division, Department of Medicine, Washington University School of Medicine, St Louis, Missouri"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"E. John","family":"Orav","sequence":"additional","affiliation":[{"name":"Division of General Internal Medicine and Primary Care, Department of Medicine, Brigham and Women\u2019s Hospital, Boston, Massachusetts"},{"name":"Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Anne M.","family":"Butler","sequence":"additional","affiliation":[{"name":"Infectious Diseases Division, Department of Medicine, Washington University School of Medicine, St Louis, Missouri"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karen E","family":"Joynt Maddox","sequence":"additional","affiliation":[{"name":"Center for Advancing Health Services, Policy & Economics Research, Washington University, St Louis, Missouri"},{"name":"Cardiology Division, Department of Medicine, Washington University School of Medicine, St Louis, Missouri"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"10","published-online":{"date-parts":[[2026,6,12]]},"reference":[{"issue":"3","key":"zoi260502r1","doi-asserted-by":"publisher","first-page":"267","DOI":"10.1016\/j.jacc.2021.10.045","article-title":"Rural-urban disparities in outcomes of myocardial 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