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Facts about the SARS-CoV-2 virus and COVID-19 disease

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The SARS-CoV-2 coronavirus was discovered in January 2020. New knowledge about the outbreak, the disease and risks will be regularly updated.

Foto: CDC, Alissa Eckert
Foto: CDC, Alissa Eckert

The SARS-CoV-2 coronavirus was discovered in January 2020. New knowledge about the outbreak, the disease and risks will be regularly updated.


About the virus

The coronavirus family includes many different viruses that can cause respiratory infection. Many coronaviruses only cause colds, while others can cause more serious illness and in some cases, death.

The novel coronavirus SARS-CoV-2 was first discovered in January 2020. It has some genetic similarities to the SARS virus (Severe Acute Respiratory Syndrome) which also belongs to the coronavirus family. The virus that causes MERS (Middle East Respiratory Syndrome) is another coronavirus. 

Coronaviruses are also detected in animals. In rare cases, these coronaviruses can develop so they can transmit from animals to humans and between humans, as seen during the SARS epidemic in 2002. The infection probably came from bats via civet cats and other animals.  and , where dromedary camels were the source of infection for the MERS virus discovered in 2012.

The new coronavirus is believed to come from bats and was transmitted to humans in the end of 2019, either directly or via other animals, but this has not been determined. There is no documentation that mutations (changes in genetic material) that have appeared since the virus was discovered have had any effect on the virus' ability to cause disease.

Research indicates that coronaviruses (including current information about the new virus) can survive on surfaces from a few hours to several days. This will vary under different conditions, such as type of surface, temperature, sunlight and air humidity. We know less about the virus transmits further from different surfaces.

Transmission

SARS-CoV-2 is mainly spread by droplet and contact transmission with near contact (1).

As with colds and influenza, the virus is transmitted from the respiratory tract of a sick person in three ways;

  • Droplet transmission: When someone who is contagious coughs, sneezes, or talks/sings, small droplets that contain virus are flung into the air. The droplets fall down quickly, usually within a metre, but people who stand close enough can breathe in the virus, or it comes into contact with the mucosa of their eyes, nose or mouth.
  • By direct contact. The person who is sick has the virus on their hands from their own saliva or airway secretions and transmits it by contact with others, for example, when shaking hands. They then transfer the virus from their hands to the mucosa of their eyes, nose or mouth.
  • By indirect contact. The virus is transmitted onto objects or surfaces (e.g. door handles, keyboards, telephones etc) by sneezing or coughing, or when the sick person has the virus on their hands, and then others touch the contaminated object/surface.

A systematic review from the Norwegian Institute of Public Health shows that it is difficult to gather sufficient evidence for how many of the COVID-19 patients were infected by each of the transmission routes.  There is still insufficient knowledge to be certain about what role airborne transmission plays in transmission of SARS-CoV-2 outside the healthcare sector. However, it can be summarised that there is currently no evidence that airborne transmission plays a key role in the transmission of COVID-19. Healthcare personnel should nevertheless use protection against airborne transmission when aerosol-generating procedures are used in hospitals.

The virus has been detected in faeces (stools), blood and urine, but it has none been shown that anyone has been infected by contact with these bodily fluids.

Current knowledge indicates that transmission mainly occurs from sick people with symptoms, or just before symptoms arise (1-2 days) (presymptomatic carriers). Some people can be infected by SARS-CoV-2 without developing symptoms, but lead to further transmission of others (asymptomatic carriers). It is not yet clear how often this happens, but it can be assumed to account for a small amount of transmission.

More about transmission 

Droplets smaller than 100 micrometres (µm) easily evaporate, depending on temperature and air humidity, and create very small droplets, called aerosols. Aerosols smaller than 5 µm can remain suspended in the air for a long time. Some medical procedures, known as aerosol-generating procedures, increase the risk of generating aerosols. Some studies have shown a few examples of aerosol transmission outside the healthcare service, where people were indoors and had not maintained the recommended distance over a longer period. This could mean that aerosols could reach the airways or hands of others that contain enough viable virus to infect others. 

Several studies show that SARS-CoV-2 tends to transmit between people who are near to each other. Indirect transmission, when the virus has landed on a surface (fomites) can occur, although this research is carried out in a laboratory or hospital, and it is unclear to what degree such indirect contact transmission is important to transmission in society. A mathematical model study indicates that contributions from indirect contact transmission can be much lower than for direct contact, but these results are uncertain. 

Infection from food, water and animals

Currently, there are no known cases of infection via food produced in Norway or imported, or from water and animals. Based on current knowledge of coronaviruses, infection via food and water is considered unlikely. So far, no information has emerged of transmission between animals and humans. In the Netherlands and Denmark, SARS-CoV-2 has been detected in mink that are believed to be have been infected by keepers. Infection of mink or other animals does not appear to have a role in transmission of the virus. It is nevertheless important that people with COVID-19 or people in quarantine do not go to work as keepers and have close contact with mink.

In the case of swimming pools, the chlorine content of the pool water will be sufficient to inactivate coronaviruses and other viruses. However, physical contact in changing rooms and by the pool could lead to transmission as with any other close contact. 

Wastewater surveillance 

Research activities are ongoing, both internationally and nationally, to look at the possibilities for  COVID-19 surveillance by analysing wastewater. Testing of SARS-CoV-2 in wastewater is also offered by some laboratories in Norway. At present, we have insufficient knowledge to assess the value of this type of surveillance and the Norwegian Institute of Public Health does not recommend implementing this type of testing in municipalities until more knowledge is available. Test capacity in Norway is now good and it is recommended that anyone with symptoms of COVID-19 is tested, see: Test criteria. Currently, this is our most important tool to detect infection early.

How contagious is it? (R0)

Calculations from China estimate that a person infected with coronavirus infects 2-3.6 others on average (2-4). In comparison, a person with influenza will infect 1-2 people. The calculations for coronavirus are currently very uncertain and will probably be lower in Norway because we have a lower population density and have implemented measures to limit transmission. 

Incubation

The incubation time (from infection until symptoms appear) is estimated by WHO to be 5-6 days but this can vary from 0 to 14 days.

Symptoms and disease

The new coronavirus causes respiratory infections, ranging from mild symptoms to severe disease and, in rare cases, death.

Some people may have COVID-19 without developing symptoms. This is especially true for children and younger adults. It is unclear to what extent people without symptoms can transmit the disease.

Usually, people who become ill initially experience upper respiratory tract symptoms (sore throat, cold symptoms, mild cough), as well as feeling generally unwell and having muscle pain. Stomach pains may be present and diarrhoea may occur in some cases. The loss of the senses of smell and taste have been reported in several countries.

The course of the disease varies widely between individuals. Currently, the typical courses appear to be:

  • Mild course: This applies to the majority of people who become sick. Symptoms pass within one to two weeks. These people rarely need treatment from the healthcare service.
  • Moderate course: After 4-7 days of mild symptoms, some people may develop pneumonia with breathing difficulties, worsening cough and rising fever. Some will need to be admitted to hospital. X-ray examination of the lungs may show changes consistent with viral pneumonia (pulmonary infiltrates)
  • Severe course: As for the moderate course, but these people also need intensive care treatment. They may have symptoms for 3-6 weeks. As for other serous infections, different complications can arise with severe COVID-19, including lung damage, cardiovascular disease and coagulation disturbances (5-8). Some people who become seriously ill may die. 

Information about risk factors for severe disease is currently limited. Admission to hospital, intensive care treatment and death are more common among the elderly and people with underlying diseases, particularly among the elderly with underlying diseases, but can also occur among people without known risk factors.

There is no specific treatment or vaccine for the disease.

 

More about the symptoms of COVID-19

It appears that SARS-CoV-2 mainly infects upper and lower respiratory tract cells and causes respiratory tract infection with symptoms such as cough, fever and sore throat. Most people who get COVID-19 only develop these symptoms.

A minority enter a more severe phase with breathing difficulties and symptoms of systemic disease that are probably caused by the body's immune response to the infection. There is a good basis to assume that SARS-CoV-2 also infects the gastrointestinal tract, and related symptoms are frequently reported.

We are learning more about the symptoms of COVID-19. Much of the knowledge is based on patients admitted with severe disease. These account for about 20 per cent of all people who develop symptoms and probably do not reflect the overall clinical presentation.

The most frequently reported symptoms of COVID-19 are fever (22-83 %) and cough (25-70 %) (9). In addition, the following are frequently reported: muscle aches (7-31%), fatigue / weakness (13-20%), headaches (18-43%), altered sense of taste and smell (2-54%), runny nose (6- 28%), chills (2-15%) and sore throat (6-30%) (10-13).

These mild symptoms are often reported when people with COVID-19 are identified by screening or follow-up of close contacts. Therefore, these symptoms are probably present among all cases of COVID-19 disease that cause symptoms, but the milder symptoms may go unnoticed when a person has other, more severe symptoms.

Shortness of breath (dyspnoea) is frequently reported (15-40 %) and is an indication of severe disease that often requires hospitalisation. The proportion that develops shortness of breath appears to be small if mild cases are included in the calculation (11).

Gastrointestinal symptoms such as pain, nausea / vomiting and diarrhoea have been reported in 2-40 % of cases. In one meta-study of 4243 patients, 17.6 % of patients had gastrointestinal symptoms (14), which may be the first and, in some cases, the only obvious symptom of the disease (15, 16).

Neurological symptoms other than headache and changes in senses of taste and smell. These may include dizziness, altered mental state, ataxia and tremor. Cases of diarrhoea and haemorrhagic strokes, encephalopathy and Guillain-Barré are also linked to SARS-CoV-2 infection (15, 17, 18).

There have been no certain findings of the virus in the central nervous system, and the mechanisms behind these neurological symptoms are unclear.

In addition, symptoms have been reported for most organ systems such as the eye (e.g., conjunctivitis), skin (rash), heart (myocarditis, arrhythmias, infarction) and kidneys (acute kidney damage) associated with the disease (9, 15, 19, 20).

Coagulation disorders

Coagulation disorders appear to occur frequently in seriously ill COVID-19 patients, but are also described among patients with mild disease. This may explain symptoms such as blood clots in the lungs (pulmonary embolism) and deep vein thrombosis, and also some of the neurological and cardiovascular symptoms described above. (9, 13-16, 21).

Silent hypoxia

There is an increase in the number of reports of COVID-19 patients with hypoxia without dyspnoea or other symptoms of hypoxia. The clinical significance of this is currently unknown, but frequent measurement with an oximeter may be considered in COVID-19 patients at risk of a severe course (for example, in a hospital). Patients with silent hypoxemia should be assessed by a doctor for possible causes, such as pulmonary embolism.

Symptoms of COVID-19 among the elderly

High age is the most certain risk factor for severe disease and death from COVID-19.

Elderly patients often have an atypical clinical presentation with many diseases (22) and this also applies to COVID-19 (23, 24). In addition to the symptoms mentioned above, there are a number of atypical symptoms that occur among the elderly with COVID-19, such as delirium (acute onset of cognitive failure and altering emotions and behaviour), confusion (new-onset or deterioration), tendency to fall (new-onset or deterioration), lethargy and weakness (new-onset or deterioration), generally poorer function level, weight loss, decreased appetite. Elderly people with dementia have a significantly increased risk of delirium with infections. These symptoms may overshadow other and more common symptoms of infection, such as respiratory problems (24).

The reason why older people more often present with atypical symptoms may be age-related changes in the immune system, temperature regulation may be poorer, and the ability to remember and recall symptoms may be impaired. Elderly people also more often have underlying chronic conditions that can affect the clinical presentation, e.g., strokes and other neurological disorders can impair the cough reflex (25).

Therefore, COVID-19 should be considered as a differential diagnosis among the elderly, even with atypical and / or mild symptoms.

Symptoms that are particularly important to be alert for in this group are tachypnea (rapid breathing), tachycardia (rapid heartbeat), hypotension (low blood pressure) and low-grade fever (above 37.5 °C).

The assessment of elderly patients should be made by people who are familiar with the patient’s normal functional level so that changes can be detected quickly; Here, both health professionals and relatives can play a role. An early diagnosis will ensure the best possible treatment and prevent the spread of infection, especially in hospital and nursing homes.

Symptoms among children

Children appear to have a similar clinical presentation to adults, but the proportion with severe disease is much lower. Most have symptoms of colds, such as cough, fever and sore throat, which last from several days to a week.

Fever (41-48 %) and cough (39-48 %) are the two most common symptoms. A sore throat was observed among 46 % in one study. Other relatively frequently reported symptoms are diarrhoea (7-9 %), nausea / vomiting (6 %), lethargy (7.6 %), mucus and runny nose (7.6 %). Other rarer symptoms include stuffy nose, headache, abdominal pain and shortness of breath (26, 27).

Multisystemic Inflammatory Disease in Children (Kawasaki-like disease)

At the end of April 2020, British health authorities reported that an increasing number of children were admitted to intensive care with symptoms similar to Kawasaki disease. Kawasaki disease is an acute condition with inflammation of the blood vessels in different parts of the body and usually affects children under 5 years.

The condition is characterised by fever lasting for more than 5 days, rash, mucosal changes on the lips and mouth, eye inflammation without pus, swollen lymph nodes on the neck and swollen / red hands and feet. The most serious complication of Kawasaki disease is that some of the children may develop aneurisms on their coronary arteries. There is no test to confirm the disease, and the diagnosis is based on the composite clinical presentation.

Kawasaki disease is rare. In Norway, 10-20 children under 5 years of age are detected annually. These children are hospitalised due to fever and poor general condition. Kawasaki disease is not contagious, but is probably triggered by an infection among children with unknown genetic risk or vulnerability. The treatment consists of giving immunoglobulin, anti-inflammatory medication and treatment to relieve symptoms. The prognosis is good, and most children recover completely within 1-2 weeks.

Among children / adolescents who have had Kawasaki-like disease during the pandemic, coronavirus has been detected in some, but not in others. The average age of those who become ill is higher than that of normal Kawasaki disease; some adolescents have also become ill. The clinical presentation is different from Kawasaki in that there are more often gastrointestinal symptoms and abnormally low blood pressure. Patients have received the same treatment as for Kawasaki disease. Most of them are in recovery or are discharged from hospitals. The association with the coronavirus is uncertain, but paediatricians, NIPH, European Centre for Disease Control (ECDC) and the World Health Organization (WHO) are following the situation closely.

On 15th May 2020, the ECDC and WHO issued their definition of the condition, i.e., which combined symptoms can give suspicion of this syndrome. There is no test to confirm this Kawasaki-like disease. Both probably cause an overreaction in the immune system in connection with, or after, an infection. WHO calls the syndrome “Multisystem inflammatory syndrome in children and adolescents temporally related to COVID-19”, while ECDC calls it “Paediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2 infection”.

ECDC and WHO stress that COVID-19 mainly causes mild illness among children, and that it is extremely rare for children to become seriously ill. The most important advice for parents is the same as always: they should seek medical attention when a child with a fever has a poor general condition and they are concerned for their child, for whatever reason.

ECDC and WHO's assessments can be found here:

References

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Facts

Coronavirus

SARS-CoV-2 is the name of the virus that is causing the outbreak of COVID-19 disease.

The virus is related to another coronavirus that caused the SARS outbreak in 2002/2003 but is not the same virus.