More than a quarter of health care workers who reported mild cases of Covid-19 had one or more long-term symptoms that lasted for at least two months, according to a research letter in JAMA.

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Study details

For the study, Charlotte Thålin of the department of clinical sciences at Danderyd Hospital in Sweden and colleagues assessed data collected as part of the Covid-19 Biomarker and Immunity (COMMUNITY) study, which "investigates long-term immunity after mild Covid-19." According to Medscape, the study enrolled health care professionals between Apr. 15, 2020, and May 8, 2020, taking blood tests at the time of enrollment and again every four months.

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The researchers enrolled a cohort of 323 hospital employees who had mild cases of Covid-19. Participants in this cohort were "seropositive for SARS-CoV-2 anti-spike IgG," according to the research letter, and reported either no symptoms or mild symptoms. Those who tested seropositive and reported severe symptoms were excluded. This cohort had a median age of 43 years, and 83% of them were women.

The researchers also enrolled 1,072 employees who did not contract Covid-19 during the study in the control group. The control group, with a median age of 47, was 86% female.

Eight months following enrollment, the study participants used a smartphone app to self-report the existence, duration, and severity of 23 predefined symptoms. According to Medscape, the researchers relied on the Sheehan Disability Scale to determine respondents' functional impairment.

Most common long-term symptoms

Overall, the study found that 26% of the Covid-19 cohort reported at least one moderate-to-severe symptom that lasted for at least two months, with just 9% of the control cohort reporting the same. By eight months, 14.9% of the Covid-19 cohort and 3.4% of the control cohort reported at least one moderate-to-severe symptom.

The top 10 most common moderate-to-severe symptoms were:

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• Anosmia (loss of smell)
  • Covid-19 cohort: 14.6% at two months and 9% at eight months
  • Control cohort: 0.6% at two months and 0.1% at eight months

• Fatigue
  • Covid-19 cohort: 8.4% at two months and 4% at eight months
  • Control cohort: 5.3% at two months and 1.5% at eight months

• Ageusia (loss of taste)
  • Covid -19 cohort: 7.7% at two months and 3.7% at eight months
  • Control cohort: 0.6% at two months and 0.1% at eight months

• Dyspnea (labored breathing)
  • Covid-19 cohort: 4.3% at two months and 1.9% at eight months
  • Control cohort: 1.1% at two months and 0.3% at eight months

• Sleeping disorder
  • Covid-19 cohort: 3.1% at two months and 2.2% at eight months
  • Control cohort: 2% at two months and 0.8% at eight months

• Headache
  • Covid-19 cohort: 2.8% at two months and 1.5% at eight months
  • Control cohort: 3.2% at two months and 1% at eight months

• Palpitations
  • Covid-19 cohort: 2.5% at two months and 0.6% at eight months
  • Control cohort: 1.7% at two months and 0.7% at eight months

• Concentration impairment
  • Covid-19 cohort: 2.2% at two months and 0.6% at eight months
  • Control cohort: 1.1% at two months and 0.2% at eight months

• Muscle or joint pain
  • Covid-19 cohort: 1.9% at two months and 0.6% at eight months
  • Control cohort: 1.8% at two months and 0.4% at eight months

• Memory impairment
  • Covid-19 cohort: 1.5% at two months and 0.3% at eight months
  • Control cohort: 1% at two months and 0.3% at eight months

According to the researchers, 11% of the Covid-19 cohort at eight months said at least one symptom negatively affected their personal or professional life, compared with just 2% of the control group. Specifically, the researchers found that: 

• 15% of the Covid-19 participants said their long-term symptoms disrupted their social life, compared with 6% of the control cohort

• 12% of the Covid-19 participants said their long-term symptoms disrupted their home life, compared with 5% of the control cohort

• 8% of Covid-19 participants said their long-term symptoms disrupted their professional life, compared with 4% in the control cohort

The researchers acknowledged several limitations to the study, including potential recall bias and the subjective rating of symptoms.

Comments

Thålin said while previous research has identified severe long-term symptoms among those who were hospitalized with Covid-19, "there is limited data on the long-term effects after mild Covid-19, and these studies are often hampered by selection bias and [are] without proper control groups."

The latest findings, however, demonstrate that "[e]ven if you are young and previously healthy, a mild Covid-19 infection may result in long-term consequences." She added that while the loss of smell and taste, in particular, "may seem trivial, [they] have a negative impact on work, social, and home life in the long run."

Separately, David Putrino, director of rehabilitation innovation at Mount Sinai Health System, said the study "tracks with a lot of the other work we're seeing." However, he pointed out that the share of people with long-term symptoms may be underestimated in the study because the antibodies used to identify those in the Covid-10 cohort "are not an entirely reliable biomarker. So what the researchers are using here is the most conservative measure of who may have had the virus."

Lekshmi Santhosh, physician faculty lead at the University of California-San Francisco's Post-COVID OPTIMAL Clinic, said the findings "ad[d] to the growing body of literature showing that people recovering from COVID have reported a diverse array of symptoms lasting for months after initial infection." She called for "more research…to investigate the mechanisms underlying these persistent symptoms" (McNamara, MedScape, 4/9; Havervall et al., JAMA, 4/7).