breathing difficulties.[5] People with the COVID-19 infection may have different symptoms, and their symptoms may change over time. Three common clusters of symptoms have been identified: one respiratory symptom cluster with cough, sputum, shortness of breath, and fever; a musculoskeletal symptom cluster with muscle and joint pain, headache, and fatigue; and a cluster of digestive symptoms with abdominal pain, vomiting, and diarrhea.[5] In people without prior ear, nose, or throat disorders, loss of taste combined with loss of smell is associated with COVID-19 and is reported in as many as 88% of symptomatic cases.[6][7][8]
Published data on the neuropathological changes related with COVID-19 have been limited and contentious, with neuropathological descriptions ranging from moderate to severe
]
Proportion of asymptomatic SARS-CoV-2 infection by age. About 44% of those infected with SARS-CoV-2 remained asymptomatic throughout the infection.[11]
At least a third of the people who are infected with the virus do not develop noticeable symptoms at any point in time.[11][12][13] These asymptomatic carriers tend not to get tested and can still spread the disease.[13][14][15][16] Other infected people will develop symptoms later (called "pre-symptomatic") or have very mild symptoms and can also spread the virus.[16]
As is common with infections, there is a delay between the moment a person first becomes infected and the appearance of the first symptoms. The median delay for COVID-19 is four to five days[17] possibly being infectious on 1-4 of those days.[18] Most symptomatic people experience symptoms within two to seven days after exposure, and almost all will experience at least one symptom within 12 days.[17][19]
Most people recover from the acute phase of the disease. However, some people continue to experience a range of effects, such as fatigue, for months, even after recovery.[20] This is the result of a condition called long COVID, which can be described as a range of persistent symptoms that continue for weeks or months at a time.[21] Long-term damage to organs has also been observed after the onset of COVID-19. Multi-year studies are underway to further investigate the potential long-term effects of the disease.[22]
The Omicron variant became dominant in the U.S. in December 2021. Symptoms with the Omicron variant are less severe than they are with other variants.[23]
Overview
Symptoms of COVID-19
Some less common symptoms of COVID-19 can be relatively
kidney failure
.
Some symptoms usually appear sooner than others, with deterioration usually developing in the second week.
muscle pain, and that nausea and vomiting usually appear before diarrhea.[26][non-primary source needed] This contrasts with the most common path for influenza where it is common to develop a cough first and fever later.[26] Impaired immunity in part drive disease progression after SARS-CoV-2 infection.[27] While health agency guidelines tend to recommend isolating for 14 days while watching for symptoms to develop,[28] there is limited evidence that symptoms may develop for some patients more than 14 days after initial exposure.[29]
The frequency of symptoms predominating for people with different variants may differ from what was observed in the earlier phases of the pandemic.
Delta
People infected with the Delta variant may mistake the symptoms for a bad cold and not realize they need to isolate. Common symptoms reported as of June 2021 have been headaches, sore throat, runny nose, and fever.[30][medical citation needed][31]
epidemiologist Tim Spector said in mid-December 2021 that the majority of symptoms of the Omicron variant were the same as a common cold, including headaches, sore throat, runny nose, fatigue and sneezing, so that people with cold symptoms should take a test. "Things like fever, cough and loss of smell are now in the minority of symptoms we are seeing. Most people don't have classic symptoms." People with cold symptoms in London (where Covid was spreading rapidly) are "far more likely" to have Covid than a cold.[32]
A unique reported symptom of the Omicron variant is
Fever is one of the most common symptoms in COVID-19 patients. However, the absence of the symptom itself at an initial screening does not rule out COVID-19. Fever in the first week of a COVID-19 infection is part of the body's natural immune response; however in severe cases, if the infections develop into a cytokine storm the fever is counterproductive. As of September 2020, little research had focused on relating fever intensity to outcomes.[37]
Some symptoms, such as difficulty breathing, are more common in patients who need hospital care.
Shortness of breath tends to develop later in the illness. Persistent anosmia or hyposmia or ageusia or dysgeusia has been documented in 20% of cases for longer than 30 days.[6][7]
As of July 2020, the ECDC reported a prevalence rate of ~68% for nasal obstruction, ~63% for cough, ~60% for rhinorrhoea or runny nose.[5] A June 2020 systematic review reported a 54–61% prevalence of dry cough and 22–28% for productive cough.[2]
Presence of Sars-CoV-2 virus RNA in the lung. Covid-19 lung showed virus replication in the desquamated lung epithelial cells. Ubiquitin C positive control (Left), COVSPIKE (middle), and dap B negative control (right).[42]
Cardiovascular
Coagulopathy is established to be associated with COVID-19 in those patients in critical state.
blood clots show with high risk in COVID-19 patients in some studies.[44]
Other
cardiovascular complications may include heart failure, arrhythmias, and heart inflammation.[45][46][47][48][49] They are common traits in severe COVID-19 patients due to the relation with the respiratory system.[50]
Hypertension seems to be the most prevalent risk factor for myocardial injury in COVID-19 disease. It was reported in 58% of individuals with cardiac injury in a recent meta-analysis.[51]
Several cases of
myocardium.[53][54]Endomyocardial biopsy [EMB] remains the gold standard invasive technique in diagnosing myocarditis; however, due to the increased risk of infection, it is not done in COVID-19 patients.[citation needed
As of July 2020, the ECDC reported a prevalence rate of ~70% for headache.[5] A June 2020 systematic review reported a 10–16% prevalence of headache.[2] However, headache could be mistaken for having a random relationship with COVID-19; there is unambiguous evidence that COVID-19 patients who had never had a recurrent headache suddenly get a severe headache daily because of SARS-CoV-2 infection.[58]
This symptom, if it is present at all, often appears early in the illness.[63] Its onset is often reported to be sudden. Smell usually returns to normal within a month. However, for some patients it improves very slowly and is associated with odors being perceived as unpleasant or different from they originally did (parosmia), and for some people smell does not return for at least many months.[64] It is an unusual symptom for other respiratory diseases, so it is used for symptom-based screening.[63][64]
Loss of smell has several consequences. Loss of smell increases
fire hazards due to inability to detect smoke. It has also been linked to depression. If smell does not return, smell training is a potential option.[64]
It is sometimes the only symptom to be reported, implying that it has a neurological basis separate from nasal congestion. As of January 2021, it is believed that these symptoms are caused by infection of sustentacular cells that support and provide nutrients to sensory neurons in the nose, rather than infection of the neurons themselves. Sustentacular cells have many Angiotensin-converting enzyme 2 (ACE2) receptors on their surfaces, while olfactory sensory neurons do not. Loss of smell may also be the result of inflammation in the olfactory bulb.[64]
A June 2020 systematic review found a 29–54% prevalence of olfactory dysfunction for people with COVID-19,[63] while an August 2020 study using a smell-identification test reported that 96% of people with COVID-19 had some olfactory dysfunction, and 18% had total smell loss.[64] Another June 2020 systematic review reported a 4–55% prevalence of hyposmia.[2] As of July 2020, the ECDC reported a prevalence rate of ~70% for loss of smell.[5]
A disturbance in smell or taste is more commonly found in younger people, and perhaps because of this, it is correlated with a lower risk of medical complications.[63]
Loss of taste and chemesthesis
In some people, COVID-19 causes people to temporarily experience changes in how food tastes (dysgeusia or ageusia).[63][64] Changes to chemesthesis, which includes chemically triggered sensations such as spiciness, are also reported. As of January 2021, the mechanism for taste and chemesthesis symptoms were not well understood.[64]
A June 2020 systematic review found a 24–54% prevalence of gustatory dysfunction for people with COVID-19.
ECDC reported a prevalence rate of ~54% for gustatory dysfunction.[5]
Other neurological and psychiatric symptoms
Other neurological symptoms appear to be rare, but may affect half of patients who are hospitalized with severe COVID-19. Some reported symptoms include
As of September 2020, it was unclear whether these symptoms were due to direct infection of brain cells, or of overstimulation of the immune system.[67]
A June 2020 systematic review reported a 6–16% prevalence of vertigo or dizziness, 7–15% for confusion, and 0–2% for ataxia.[2]
Blood clots and bleeding
Patients are at increased risk of a range of different blood clots, some potentially fatal, for months following COVID infection. The Guardian wrote, "Overall, they [a Swedish medical team] identified a 33-fold increase in the risk of pulmonary embolism, a fivefold increase in the risk of DVT (deep vein thrombosis) and an almost twofold increase in the risk of bleeding in the 30 days after infection. People remained at increased risk of pulmonary embolism for six months after becoming infected, and for two and three months for bleeding and DVT. Although the risks were highest in patients with more severe illness, even those with mild Covid had a threefold increased risk of DVT and a sevenfold increased risk of pulmonary embolism. No increased risk of bleeding was found in those who experienced mild infections." Anne-Marie Fors Connolly at Umeå University said, "If you suddenly find yourself short of breath, and it doesn't pass, [and] you've been infected with the coronavirus, then it might be an idea to seek help, because we find this increased risk for up to six months."[68]
chilblain-like lesions often occur only in younger patients and do not appear until late in the disease or during convalescence.[71] Certain genetic polymorphisms (in the TREX1 gene) have been linked to susceptibility towards developing COVID-toe.[72] A June 2020 systematic review reported a 0–1% prevalence of rash in COVID-19 patients.[2]
There are three stages, according to the way COVID-19 infection can be tackled by pharmacological agents, in which the disease can be classified.[75] Stage I is the early infection phase during which the domination of upper respiratory tract symptoms is present. Stage II is the pulmonary phase in which the patient develops pneumonia with all its associated symptoms; this stage is split with Stage IIa is without hypoxia and Stage IIb having hypoxia. Stage III is the hyperinflammation phase, the most severe phase, in which the patient develops acute respiratory distress syndrome (ARDS), sepsis and multi-organ failure.[75]
A similar stereotyped course was postulated to be: the first phase of an incubation period, a second phase corresponding to the viral phase, a third phase corresponding to the state of inflammatory pneumonia, a fourth phase corresponding to the brutal clinical aggravation reflected by acute respiratory distress syndrome (ARDS), and finally, in survivors, a fifth phase potentially including
lung fibrosis, and persisting in the form of "post-covid" symptoms.[76]
Following the infection, children may develop multisystem inflammatory syndrome, also called paediatric multisystem inflammatory syndrome. This has symptoms similar to Kawasaki disease, which can possibly be fatal.[77][78][79]
Around 10% to 30% of non-hospitalised people with COVID-19 go on to develop long COVID. For those that do need hospitalisation, the incidence of long-term effects is over 50%.[80] Long COVID is an often severe multisystem disease with a large set of symptoms. There are likely various, possibly coinciding, causes.[80] Organ damage from the acute infection can explain a part of the symptoms, but long COVID is also observed in people where organ damage seems to be absent.[81]
By a variety of mechanisms, the lungs are the organs most affected in COVID‑19.
DLCO, even in asymptomatic people, but with the suggestion of continuing improvement with the passing of more time.[82] After severe disease, lung function can take anywhere from three months to a year or more to return to previous levels.[85]
The risks of
cognitive deficit, dementia, psychotic disorders, and epilepsy or seizures persists at an increased level two years after infection.[86]
Post-COVID Condition
Longer-term effects of COVID-19 have become a prevalent aspect of the disease itself. These symptoms can be referred to as many different names including post-COVID-19 syndrome, long COVID, and long haulers syndrome. An overall definition of post-COVID conditions (PCC) can be described as a range of symptoms that can last for weeks or months.[21] Long COVID can be present in anyone who has contracted COVID-19 at some point; typically, it is more commonly found in those who had severe illness due to the virus.[21][87]
Symptoms
Long COVID can attack a multitude of organs such as the lungs, heart, blood vessels, kidneys, gut, and brain.[88] Some common symptoms that occur as a result are fatigue, cough, shortness of breath, chest pains, brain fog, gastrointestinal issues, insomnia, anxiety/depression, and delirium.[89] A difference between acute COVID-19 and PCC is the effect that it has on a person's mind. People are found to be dealing with brain fog and impaired memory, and diminished learning ability which has a large impact on their everyday lives.[87][90] A study that took a deeper look into these specific symptoms took 50 SARS-CoV-2 laboratory-positive patients and 50 SARS-CoV-2 laboratory-negative patients to analyze the variety of neurologic symptoms present during long COVID. The most frequent symptoms included brain fog, headache, numbness, dysgeusia (loss of taste), anosmia (loss of smell), and myalgias (muscle pains) with an overall decrease in quality of life.[87]
^"Considerations for quarantine of contacts of COVID-19 cases". World Health Organization. WHO recommends that all contacts of individuals with a confirmed or probable COVID-19 be quarantined in a designated facility or at home for 14 days from their last exposure.
. Notably, these incubation periods longer than 14 days were registered not only in sporadic cases, but in a substantial proportion reaching... 5.0% out of 339, 7.7% out of 104... patients with traced contacts
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