Long COVID can affect nearly every organ system, with sequelae (consequences) including respiratory system disorders, nervous system and neurocognitive disorders, mental health disorders, metabolic disorders, cardiovascular disorders, gastrointestinal disorders, musculoskeletal pain, and anemia. A wide range of symptoms is commonly reported, including fatigue, malaise, headaches, shortness of breath, anosmia (loss of smell), parosmia (distorted smell), muscle weakness, low fever, and cognitive dysfunction.
The exact nature of symptoms and the number of people who
experience long-term symptoms are unknown; these vary according to the
definition used, the population being studied, and the time period used in the
study. A survey by the UK Office for
National Statistics estimated that about 14% of people who
tested positive for SARS-CoV-2 experienced
one or more symptoms for longer than three months. A study from the
University of Oxford of 273,618 survivors of COVID-19, mainly from the United
States, showed that about 37% experienced one or more symptoms between three
and six months after diagnosis.
While studies into various aspects of long COVID are underway, as
of November 2021, the definition of the illness is still unclear, as is its
mechanism. Health systems in some countries and
jurisdictions have been mobilized to deal with this group of patients by
creating specialized clinics and providing advice. Overall, however, it is
considered by default to be a diagnosis of
exclusion.
A review suggests that global
prevalence of long COVID conditions after infection could be as high as 43%,
with the most common symptoms being fatigue and
memory problems.
World Health Organization clinical case definition
The World Health
Organization (WHO) established a clinical case
definition in October 2021, published in the journal The Lancet
Infectious Diseases:
post-COVID-19
condition occurs in individuals with a history of probable or confirmed
SARS-CoV-2 infection, usually 3 months from the onset, with symptoms that last
for at least 2 months and cannot be explained by an alternative diagnosis.
Common symptoms include, but are not limited to, fatigue, shortness of breath,
and cognitive dysfunction, and generally have an impact on everyday
functioning. Symptoms might be new onset following initial recovery from an
acute COVID-19 episode or persist from the initial illness. Symptoms might also
fluctuate or relapse over time.
Symptom
A multinational online survey with 3,762 participants with
illnesses lasting more than 28 days found that recovery takes longer than 35
weeks for 91% of them. On average, participants experienced 56 symptoms
(standard deviation ± 25.5) in nine organ systems. Symptoms varied over time,
and the most common symptoms after six months were fatigue, post-exertional
malaise, and cognitive dysfunction.
Symptom relapse occurred
in 86% of participants triggered by physical or mental effort or by stress. Three
groups of symptoms were identified: initial symptoms that peak in the first two
to three weeks and then subside; stable symptoms; and symptoms that increase
markedly in the first two months and then stabilize.
A study from the Office for National Statistics with 20,000 participants, including children
and adults, found that, in children who tested positive, at least one symptom
persisted after five weeks in 9.8% of children aged two to eleven years and in
13% of children aged 12 to 16 years. A 2022 University College London study in the UK, found that children ages 11–17 who had
a positive PCR test for COVID were more likely to have three or more symptoms
three months after their diagnosis compared to those with a negative test. A
study in Italy, which analyzed 129 children under the age of 18, examined
health data obtained via a questionnaire between September 2020 and 1 January
2021. 53% of the group experienced COVID-19 symptoms more than 120 days after
their diagnosis, and 43% were still impaired by the symptoms. Symptoms included
insomnia, fatigue, muscle pain, chest tightness and pain, nasal congestion,
tiredness, and difficulty concentrating. A case report of five
children in Sweden also reported symptoms (fatigue, heart palpitations, dyspnea,
headaches, muscle weakness, and difficulty concentrating) persisting for 6–8
months after diagnosis.
Epidemiology
In June 2022, a CDC study based on electronic
health records showed that "one in five COVID-19 survivors
aged 18–64 years and one in four survivors aged ≥65 years experienced at least
one incident condition that might be attributable to previous COVID-19" or
long COVID and analysis of private healthcare claims showed that of
78,252 patients diagnosed with 'long COVID', 75.8% had not been hospitalized
for COVID-19.
As of January 2021, the precise incidence was unknown. The
incidence declines over time as many people slowly recover. Some early studies
suggested that between 20% and 33% of people with COVID-19 experienced symptoms
lasting longer than a month. A telephone survey in the U.S. in the first
half of 2020 showed that about 35% of people who had tested positive for
SARS-CoV-2 experienced a range of symptoms that lasted longer than three weeks. As
of December 2020, the Office of
National Statistics in the UK estimated that, of all people
with a positive test for SARS-CoV-2,
about 21% experienced symptoms for longer than five weeks, and about 10%
experienced symptoms for longer than 12 weeks.
Although anyone who gets infected can develop
long COVID, people who become so sick that they require hospitalization take
longer to recover. A majority (up to 80%) of those who were admitted to the hospital with severe disease experience long-term problems including fatigue
and shortness of breath (dyspnoea). Patients with severe initial
infection, particularly those who required mechanical ventilation to help breathing, are also likely to develop post-intensive care syndrome following recovery.
Some people develop long-term neurological
symptoms despite never having been hospitalized for COVID-19; the first study
on this population was published in March 2021. Most frequently, these
non-hospitalized patients experienced "prominent and persistent 'brain
fog' and fatigue that affect their cognition and quality of life."
Predominance Symptoms in Long COVID
Fatigue describes a state
of tiredness that does not resolve with rest or sleep. In general usage,
fatigue is synonymous with extreme tiredness or exhaustion that normally
follows the prolonged physical or mental activity. When it does not resolve after
rest or sleep or occurs independently of physical or mental exertion, it may
be a symptom of a medical condition that may become severe or progressive.
Fatigue can be a feature of a mental disorder such as
depression; may be associated with conditions of chronic pain such as fibromyalgia; it may also feature in
conditions of chronic low-level inflammation, and be a disease-related symptom
in many other conditions. Fatigue often has no known cause, and is recognized
as being very complex in nature. Fatigability describes a susceptibility
to fatigue.
One study concluded about 50% of people who
have fatigue receive a diagnosis that could explain the fatigue after a year
with the condition. In those people who have a possible diagnosis,
musculoskeletal (19.4%) and psychological problems (16.5%) are the most common.
Definitive physical conditions were only found in 8.2% of cases.
Depression and other psychological conditions can
produce fatigue, so people who report fatigue are routinely screened for these
conditions, along with substance use disorders, poor diet, and lack of physical exercise, which paradoxically increases fatigue.
Clouding of consciousness (also known as brain fog or mental fog or brain fuzz) occurs when a person is slightly less wakeful or aware than normal. They are not as aware of time
or their surroundings and find it difficult to pay attention. People describe this subjective sensation as their mind being "foggy"
The emerging concept of sluggish
cognitive tempo has also been implicated in the expression of
'brain fog' symptoms.
Patients recovering from COVID-19 report experiencing 'brain
fog', which can reflect a wide variety of neurological and psychological symptoms linked to
COVID-19.
Many people with fibromyalgia experience cognitive
problems (known as "fibrofog" or "brainfog"), which
may involved impaired concentration, problems with short- and long-term memory, short-term memory
consolidation, working memory, impaired speed of
performance, inability to multi-task, cognitive overload, and diminished attention span. About 75% of fibromyalgia
patients report significant problems with concentration, memory,
and multitasking. A
2018 meta-analysis found that the largest
differences between fibromyalgia patients and healthy subjects were in inhibitory
control, memory, and processing speed. It
is hypothesized that the increased pain compromises attention systems, resulting in
cognitive problems.
In chronic fatigue
syndrome, also known as myalgic encephalomyelitis, the CDC's
recommended criteria for diagnosis include that one of the following
symptoms must be present:
·
Problems with thinking and memory (cognitive dysfunction,
sometimes described as "brain fog")
·
While standing or sitting upright; lightheadedness, dizziness,
weakness, fainting, or vision changes may occur (orthostatic
intolerance)
