Toward characterizing brain fog in long COVID: correlates and impact on measurement metrics

Brain fog is reported in 20–30% of patients with Long COVID. This study extends prior research linking brain fog to a limited set of psychosocial factors by examining a broader range of factors. We also examine how brain fog may impact the reliability and validity of self-reported measures.

This longitudinal cohort study utilized baseline (May–July 2020) and follow-up 3 (January–April 2023) data to compare individuals who strongly endorsed (n = 107) or strongly rejected (n = 374) having brain fog. We examined group differences in demographics, COVID-specific stressors, perspective changes, cognitive-appraisal processes, and the psychometric functioning of the PROMIS-10 Physical Health scale.

Individuals with and without brain fog differed with respect to various demographic characteristics, occupational complexity, and financial strain. Those with brain fog had worse baseline cognitive health; more comorbidities; higher levels of COVID-specific and general stressors; lower levels of social support and salutogenic health habits; and worse perceptions of social-norm changes. They were increasingly focused inward and tended to focus on the negative, to compare themselves to external standards, and to focus less on getting better or adjusting to their situation. Measurement-metric differences included lower item means, factor loadings, and explained variance in the unidimensional factor model; worse fit indices; and non-significant trends of lower item-total correlations and internal consistency reliability. There was evidence of measurement non-invariance and DIF for the fatigue item.

Brain fog is associated with varied demographic and psychosocial factors. Individuals with brain fog demonstrated “noisy” measurement, which may have important health outcomes research implications.