In a recent study published in the journal Nature CommunicationsThe researchers examined the natural history of long COVID in a general population cohort.
Understanding the natural history and scale of long COVID is essential for health and social planning. Most studies report the prevalence of long COVID at a single time point after infection, and there is limited information on temporal changes in long COVID. Furthermore, studies with serial outcome measures have been restricted to selected population subsets and specific outcomes or have lacked a comparison group. Additionally, while long COVID may remain stable in some people, it may progress, decline, or relapse in others.
Study: Natural history of long COVID in a nationwide population-based cohort study. Image Credit: Lightspring/Shutterstock
The study and the findings.
The present study examined the trajectory of long COVID in a general population cohort. The researchers used serial questionnaire data from the “Long COVID in Scotland study.” Of more than four million questionnaires, 9% were completed by 288,173 people. Of these, the team included people who consented to linking records necessary to obtain test results.
The team excluded people recruited beyond the six-month follow-up, people with asymptomatic infections, and subjects with self-reported positive test results who were not registered in the database. Therefore, of the 160,781 eligible subjects, 80,332 had a symptomatic, laboratory-confirmed coronavirus 2 (SARS-CoV-2) infection, and the remainder never had an infection.
Among infected individuals, 12,947 provided six- and 12-month follow-up questionnaire data, and 4,196 completed six- and 18-month follow-up questionnaires; the corresponding figures for uninfected subjects were 11,026 and 1,711, respectively. Six months after infection, 49.5% of subjects reported complete recovery, 43.6% reported partial recovery, and 6.9% did not recover. At 12 months, the corresponding figures were 50.8%, 41.8% and 7.4%, respectively.
Among those with partial recovery at six months, 21% and 22% improved at 12 and 18 months, while 8% and 10% reported deterioration, respectively. Among people who had not recovered by six months, 404 improved somewhat by 12 months and 28 recovered completely. Notably, 16% of subjects who fully recovered at six months reported deterioration at 12 months.
Socioeconomic deprivation and preinfection depression were more prevalent among subjects who reported impaired recovery between six and 12 months. Furthermore, among people who did not fully recover by six months, improvement was more likely among the wealthier, but less likely among people with pre-infection depression and older people.
Similarly, among those with partial or complete recovery at six months, deterioration in recovery status at 12 months was more likely among people with depression and less likely among older and wealthier subjects. The percentage of people reporting at least one of the 26 symptoms remained unchanged over time among the infected group, but increased in the uninfected group.
The prevalence of new and persistent symptoms at 12 and 18 months compared to six months was higher among previously symptomatic subjects than among uninfected subjects. There was a significant decrease in the prevalence of confusion (brain fog) and altered smell/taste between six and 12 months after infection. Notably, this reduction was specific to participants with improvements in recovery status.
Confusion was significantly more prevalent six months after infection among subjects with a history of anxiety or depression. Additionally, infected subjects reported significant increases in the prevalence of dry and productive cough from six to 12 months. However, uninfected subjects also reported these symptoms more frequently over time.
Higher prevalence of dry cough was associated with younger age and more pre-existing conditions, especially anxiety or depression. A higher prevalence of productive cough was associated with pre-existing respiratory disease and male sex. Of note, late-onset cough was specific to people who reported deterioration in recovery. The prevalence of hearing problems increased in both groups between six and 12 months, but was significantly higher in the infected group.
The higher prevalence of cough and hearing problems between six and 18 months was significant compared to the uninfected group. The mean EuroQoL-5D visual analogue scale (EQ-5D VAS) score decreased marginally six to 12 months after infection. However, a similar decrease was also observed in the uninfected group. In particular, symptomatic infection was associated with a much greater decrease in VAS score.
Taken together, the study reported the long trajectory of COVID in the general population in relation to changes in symptoms and quality of life in people who were never infected. The findings highlight no significant changes in self-reported recovery status or the percentage of people with symptoms beyond six months. However, 12% of subjects reported deterioration and an equivalent proportion had improvements in recovery. Confusion and altered smell/taste resolved over time in some people, while others had a delayed cough or hearing problems.