Two-year trajectories of COVID-19 symptoms and their association with illness perception: A prospective cohort study in Amsterdam, the Netherlands 6 189 This highlights that analysis of long COVID symptoms should account for non-linear symptom progression, to ensure that the presence of symptoms is not underestimated. Our study is not the first to explore the non-linear progression of specific long COVID symptoms. Using Markov models, a study based in France[20] found that the prevalence of approximately half (51%) of long COVID symptoms decreased over a one-year period, whereas the proportion of participants reporting parasthaesia and hair loss appeared to increase over the same period. The longer follow-up time of our cohort allowed us to examine symptom progression beyond the first year. This revealed a relapse in the proportion of participants reporting myalgia and dyspnoea between months 12-24 after illness onset despite an overall improvement in the first year, suggesting a non-linear course of long COVID symptoms may not be confined to the first year since illness onset. Symptom trajectories were also highly congruent with illness perception when adjusting for age, sex, initial COVID-19 severity, and timing of infection. These findings are in line with a previous longitudinal study that found higher B-IPQ scores at one year after COVID-19 among individuals with a greater number of long COVID symptoms, reduced physical performance and higher fatigue score[21]. Whilst we cannot proclaim a causal relationship, this association observed has two important implications. Firstly, in clinical practice, our findings imply that the B-IPQ – a rapid assessment tool – could be used to quantify long COVID severity in real-time, monitor individuals’ progression over time, or screen individuals for risk of developing more severe long COVID, as suggested by the association between the month 1 B-IPQ and belonging to a 24-month trajectory with a greater number of symptoms. Secondly, our findings help validate using the total mean number of long COVID symptoms as a measure of subjective experience of long COVID, including differentiation of long COVID severity. Indeed, individuals belonging to Trajectory 4 scored significantly higher on all domains of the B-IPQ except treatment control at months 6 and 12 of follow-up. Participants are likely to have demonstrated a negative perception of treatment control regardless of the total symptom trajectory due to the lack of treatment options for long COVID. In addition, we observed that individuals infected during the first wave tended to have more negative illness perception compared to those infected during subsequent waves, despite having lower odds of being allocated to Trajectory 4. This demonstrates that illness perception can be influenced by external factors, such as fear around COVID-19 during the first months of the pandemic[22]. Together, our findings infer that efforts to cultivate a more positive illness perception may help alleviate the impact of long COVID and that further investigation of utilising the B-IPQ in clinical practice is required.
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