Long COVID and Incident Multimorbidity in the United States: Evidence from a Nationally Representative Longitudinal Study

Background/Objectives: Long COVID has been associated with elevated risks of individual chronic conditions, but its association with the transition to multimorbidity remains unclear. This study aims to examine whether retrospective COVID-19 status was associated with incident multimorbidity among U.S. adults. Methods: We analyzed Panel 24 of the Medical Expenditure Panel Survey (MEPS; 2019–2022), including 4356 individuals free of multimorbidity at baseline. COVID-19 exposure was classified as Long COVID, COVID-19-recovered, or no COVID-19. Survey-weighted logistic regression estimated associations between retrospective COVID-19 status and incident cross-domain multimorbidity, and generalized estimating equations assessed healthcare expenditures, health-related quality of life, and inpatient utilization. Results: Incident MM occurred in 106 participants: 17 with Long COVID, 41 COVID-19-recovered, and 48 with no COVID-19. In the primary model (4239 participants; 105 events), Long COVID was associated with higher odds of incident MM than no COVID-19 (OR 2.34; 95% CI, 1.14–4.79); the estimate for COVID-19-recovered participants was OR 1.71 (95% CI, 1.01–2.92). Fully adjusted and Firth estimates were directionally consistent. Cardiometabolic plus respiratory MM predominated (79/106). COVID-status-by-year interactions were not significant for total expenditures, out-of-pocket expenditures, physical or mental health scores, or inpatient stays. Conclusions: Retrospectively classified Long COVID was associated with incident cross-domain MM recorded during follow-up, but temporal ordering cannot be established, and sparse events limit precision. Replication with prospectively timed exposure and diagnosis data is needed.