OBJECTIVES: This study investigates the impact of COVID-19 on national disease dynamics amidst the ongoing pandemic, aiming to understand the implications for future outbreaks.

METHODS: National insurance open data from South Korea were utilized for interrupted time series (ITS) analyses. The dataset covered monthly patient counts from January 2010 to August 2022. For the ITS analysis, five variables were considered: time, a COVID-19 dummy variable, time after COVID-19, an Omicron dummy variable, and time after Omicron. The outcome variables consisted of the number of patients per month. A generalized linear square model with AR1 correlation was employed, accounting for autoregression. To determine the impact of a specific disease, a positive impact was defined if both dummy variable and time coefficients were significantly positive, and a negative impact if both coefficients were significantly negative.

RESULTS: Among the analyzed 1,649 ITS models, six diseases (e.g., "absent, scanty and rare menstruation", "hyperaldosteronism", “maternal infectious and parasitic disease”, “other and unspecified infectious disease”, and “other sepsis”) showed a positive COVID-19 impact on prevalence, while 22 diseases (e.g., “acute pancreatitis”, “failure and rejection of transplanted organ”, “Cushing’s syndrome”, “paraplegia”, “schizoaffective disorders”, and “disturbances of smell and taste”) exhibited a negative impact (p<0.05).

CONCLUSIONS: The impact of COVID-19 on diseases is influenced by factors such as direct virus effects and policy measures. Diseases negatively associated with COVID-19 may be influenced by policies that hindered access to medical services. Consequently, patients with these diseases may not seek hospital care regardless of the severity of symptoms, suggesting a potentially unfavorable prognosis for affected individuals in the future. These findings highlight the need for careful consideration of clinical strategies and policy interventions to mitigate the adverse effects of future pandemics. By leveraging the knowledge gained from this study, we can strive to develop more effective and targeted policies in anticipation of future outbreaks.