Social impact of brain fog and analysis of risk factors: Long COVID in Japanese population

Abstract

Objective: To reveal the clinical features and assess risk factors linked to brain fog and its societal implications, including labor productivity, providing valuable insights for the future care of individuals who have experienced coronavirus disease 2019 (COVID-19).

Methods: We analyzed a comprehensive cohort dataset comprising 1,009 patients with COVID-19 admitted to Japanese hospitals. To assess brain fog, we analyzed patients who responded to a questionnaire indicating symptoms such as memory impairment and poor concentration.

Results: The prevalence of brain fog symptoms decreased 3 months posthospitalization but remained stable up to 12 months. Neurological symptoms such as taste and smell disorders and numbness at hospitalization correlated with a higher frequency of identifying brain fog as a long COVID manifestation. Our findings indicated that advanced age, female sex, a high body mass index, oxygen required during hospitalization, chronic obstructive pulmonary disease, asthma, and elevated C-reactive protein and elevated D-dimer levels were risk factors in patients exhibiting brain fog. Additionally, we demonstrated the negative impact of brain fog on labor productivity by presenteeism scores.

Interpretations: This study clarified the clinical characteristics of patients experiencing brain fog as a long COVID manifestation, specifically emphasizing neurological symptoms during hospitalization and their correlation with brain fog. Additionally, the study identified associated risk factors for its onset and revealed that the emergence of brain fog was linked to a decline in labor productivity.

Figure 1

Trends of patients who had brain fog, memory impairment, and poor concentration as sequelae at 3, 6, and 12 months. The trends in patients with brain fog, memory impairment, and poor concentration are shown (A). The red area represents patients with symptoms, the blue area represents those without symptoms, and the white area represents cases in which information is missing. The blue curve illustrates the progression in individuals who remained asymptomatic during their hospital stay, whereas the red curve represents individuals who developed symptoms during hospitalization. Furthermore, we showed the distribution of patients with overlapping symptoms during hospitalization at 3, 6, and 12 months (B). The gray area represents patients with memory impairment, and the blue area represents those with poor concentration. The numbers within each circle indicate the number of patients. MI, memory impairment; PT, poor concentration.

Figure 2

Pattern of symptoms during hospitalization in patients with brain fog at either 3, 6, or 12 months. The percentages in this figure indicate how frequently patients, who had a combination of two symptoms observed during hospitalization, experienced brain fog at 3, 6, and 12 months postdiagnosis. Symptoms refer to a combination of 24 symptoms assessed during hospitalization.

Figure 3

Risk factors for having brain fog symptoms between 3, 6, and 12 months. Odds ratios (ORs) were analyzed for patients with brain fog, memory impairment, or poor concentration using risk factors identified in previous reports. BMI, body mass index; COPD, chronic obstructive pulmonary disease; CI, confidence interval; ICU, intensive care unit.

Figure 4

Brain fog causes a decrease in presenteeism values at 3, 6, and 12 months. Comparison of absolute and relative presenteeism in patients with persistent symptoms (red) and those with recovered symptoms (dark blue) at 3, 6, and 12 months after diagnosis. The horizontal dashed line represents the median, while the dotted lines indicate the upper and lower 25th percentiles. Patients with brain fog tend to have lower presenteeism scores than those without.