Associations between symptoms and of symptoms with activity in long covid: an intensive longitudinal study

Long covid (post-acute covid syndrome) is a common consequence of SARS-CoV-19 regardless of initial illness severity. Affected individuals describe multiple symptoms which vary between and within individuals. Few studies of long covid have addressed current models of interoception such as the Embodied Predictive Interoceptive Coding (EPIC) model of symptoms. Objectives To examine the extent, patterns and correlations of within-person variation in symptoms. We hypothesised that weak or inconsistent correlations between symptoms would be indicative of disordered interoception. Methods Intensive longitudinal study of 74 adults with self-reported long covid for more than 6 months. Data collection involved a smartphone app with 5 daily entries over 14 days and continuous wearing of a wrist accelerometer. Data items included 7 symptoms (visual analog scales) and perceived demand in the preceding period (Likert scales). Analysis used within-person correlations of symptoms pairs and personal symptom networks derived from graphical vector autoregression. Results Physical symptoms showed substantial within-person variability. Fatigue and overall unwellness were strongly corrrelated in all participants, but other correlations varied substantially between individuals. There were no consistent clusters of correlation patterns. Fatigue and unwellness showed weak relationships to subjective demand and no relationship to objective physical activity. Symptom networks . showed low autocorrelation between symptoms, inconsistent contemporaneous, associations between individuals and very few directed (temporal lagged) associations. Conclusion Symptoms of long covid vary within individuals over short time scales, with little apparent relationship to activity, and few common patterns of symptom correlation. This suggests that disturbed interoception may be compounding other pathophysiological mechanisms.1