Coronavirus disease 2019

COVID-19 (abbreviation for coronavirus disease 2019, also colloquially known as Corona or Covid in German-speaking countries) is a notifiable infectious disease. It is caused by the coronavirus SARS-CoV-2 and has a broad, nonspecific spectrum of symptoms. The virus was first described in Wuhan, People's Republic of China, in December 2019. It spread very rapidly worldwide and is the cause of the COVID-19 pandemic. As of June 14, 2021, more than 175 million COVID-infected people have been registered worldwide; the number of unreported cases in many countries is high. More than 3.8 million people have been registered as deaths related to COVID disease; again, the number of unreported cases is high.

Infection with SARS-CoV-2 occurs through droplet infection (inhalation of virus-laden aerosols), especially when staying in closed, (too) poorly ventilated rooms. The Robert Koch Institute (RKI) has not ruled out the possibility of smear infection through contaminated surfaces. In order to avoid infection, spatial distancing ("social distancing"), contact restriction, the wearing of a medical protective mask and hygiene measures are recommended.

There is much evidence to suggest that the spread of COVID-19 to become a global pandemic was facilitated in particular by "superspreading."

The incubation period of COVID-19 is on average five to six days; however, up to two weeks can pass between infection and the appearance of the first symptoms. Occasionally, the first symptoms appear within 24 hours of infection. It is particularly insidious that an infected person can be contagious days before the first symptoms appear, and even after they have subsided.

The course of the disease is non-specific and can vary greatly. According to RKI estimates, 55 to 85 % of infected persons have noticeable symptoms and/or show recognizable signs of disease (symptoms) or typical symptom combinations (syndrome) of a COVID-19 disease (manifestation index); the remaining infected persons are symptom-free and do not show any symptoms, i.e. they are asymptomatically ill (but can still potentially spread the virus). About 81% of registered cases have a mild course with fever or mild pneumonia, dry cough, and fatigue. Less common are a stuffy nose, headache, sore throat, aching limbs, conjunctivitis, diarrhea, vomiting, loss of taste and smell, skin rash, or discoloration of fingers or toes. In about 14% of cases, the course is more severe, and in about 5% it is so severe that patients require intensive care ventilation. In severe COVID, infected individuals develop bilateral pneumonia, suffer acute respiratory failure, and may also die. Pathological processes of the liver, central nervous system, kidneys, blood vessels and heart have also been observed.

Persistent post-disease symptoms, also called "Long COVID," are relatively common - both in those who are initially severely ill and in young, healthy people who are initially only mildly ill. They can lead to long-lasting chronic symptoms in many organ systems. In
contrast, no evidence of Long Covid
has been observed in
over 100,000 participants in COVID vaccination studies (as of December 2020). Long Covid is the subject of ongoing research.

COVID-19 has been the subject of intensive research since the beginning of the pandemic. The results are shared internationally. It is common practice to publish current studies online as preprints (rather than waiting for peer review, for example).

By the end of 2020, COVID vaccines had already been approved in the European Union and in some non-EU countries, and vaccination campaigns began. Science magazine declared the development of vaccines against SARS-CoV-2 at an unprecedented rate as the Scientific Breakthrough of the Year.

Designation

WHO established the acronym "COVID-19" as the official name on February 11, 2020. It comes from the English: CO for Corona, VI for Virus, D for Disease and 19 for the year of first description 2019.

Clinical symptoms and laboratory signs of disease

Differentiation from other viral diseases such as influenza on the basis of symptoms alone is "difficult to impossible". Other pathogens and diagnoses can also influence the clinical picture (see syndromes, comorbidity and multimorbidity), for example, cold viruses such as rhino-, entero- and mastadenoviruses, paramyxoviridae or other coronaviruses. They can be included or excluded by differential diagnosis with microbiological findings.

After an incubation period of typically 5 to 6 days (in rare cases up to 14 days), fever, muscle pain and dry cough may occur. Frequently, the disease also manifests itself with a general feeling of severe illness and also back pain.

In the further course, severe shortness of breath may develop due to an infection of the lower respiratory tract up to pneumonia. This may be accompanied by chest pain in the sense of pleurisy. The majority of patients showed the combination of a decrease in total white blood cell count, a decrease in lymphocyte count, and an increase in laboratory inflammatory parameters (such as CRP and ESR) typical of severe viral infections. Few affected individuals also suffer from rhinitis, nausea and diarrhea.

In the study by a group of British researchers, 59% of 1702 COVID patients who tested positive were found to have a loss of sense of smell (anosmia) and sense of taste (ageusia) compared to 18% in the virus-negative control group. In a smaller study by direct patient examination, approximately 70% of the patients studied showed this disease sign. At Johns Hopkins University, tissue samples from 23 COVID-19-free patients demonstrated the highest expression of the enzyme ACE2 in the area of the nose responsible for smelling, thus explaining the loss of smell upon infection.

Based on clinical observations and laboratory chemistry tests, a three-phase clinical picture is postulated. An early infection phase is followed after about five days by a phase in which the lung disease predominates. If the disease continues to progress, a phase occurs around the tenth day after the onset of symptoms, which is characterized by an excessive immune response with further increasing damage to the lungs and the heart muscle. In the last phase there is also an increase in troponin and BNP as an expression of the cardiac muscle damage and the loss of function of the organ. A diagnostic-therapeutic guideline of German pulmonary physicians comes to an almost identical assessment of this three-phase course, the early infection, the pulmonary manifestation, and the severe hyperinflammatory phase, with differentiated therapy recommendations for mechanical ventilation during the individual stages in each case.

In the report of the Chinese Center for Disease Control and Prevention (CCDC) on 44.415 cases from Wuhan, classification as mild disease is when there is no or only mild pneumonia; for severe disease, pneumonia, dyspnea, respiratory rate ≥ 30 breaths per minute, blood oxygen saturation ≤ 93%, and other clinical signs are typical; for critical disease, respiratory failure, septic shock, and/or multiple organ failure are to be expected. The case report noted 81% mild disease progression, 14% severe disease progression, and critical disease progression in 5%. Those with a mild course often have no symptoms or resolve within two weeks, according to the RKI. People with a severe course of the disease take between three and six weeks to recover from the disease.

The majority of hospitalizations of the first patients occurred after about one week of symptomatic illness due to deterioration of the condition. In those cases where intensive care treatment became necessary, its necessity arose after about ten days after symptom onset. In an epidemiologic study of 99 hospitalized cases, noninvasive ventilation was used in 13 patients, invasive ventilation in four patients, dialysis due to renal failure in nine patients, and extracorporeal lung assist (ECLA) in three patients. Clinical observations often described minor discomfort despite respiratory insufficiency measurable by equipment. Patients who were actually in need of ventilation due to low oxygen saturation were often relatively symptom-free before their condition deteriorated rapidly due to oxygen debt in the organism.

About 85% of severely ill COVID-19 patients develop lymphopenia, which is a deficiency of lymphocytes in the blood. In fatal cases, lymphopenia persists. The severely ill patients also often develop hypercytokinemia (cytokine storm). A cytokine storm results from an overreaction of the immune system. This overreaction is characterized by a marked increase in inflammation-related cytokines, such as interleukin-6, interleukin-8, interleukin-1β, and TNF-α. The increased release of these cytokines leads to an overproduction of immune cells, especially in the lung tissue. There, the immune cells release additional cytokines (co-coupling). This uncontrolled immune response leads to severe inflammatory diseases such as pneumonia, respiratory distress and airway inflammation.

Laboratory findings revealed very high ferritin levels as well as strongly elevated interleukin-6 or elevated levels of LDH, D-dimer and a persistent decrease in lymphocytes as factors for an unfavorable prognosis.

Cytokine storm and lymphopenia are grouped together as "lymphopenic community acquired pneumonia" (L-CAP). L-CAP is associated with severe disease progression, increased mortality, and misdirected immune response. It is thought that early recognition of this immunological phenotype may be useful to identify patients with severe courses in a timely manner.

According to a study evaluating the disease courses of the first 50 patients from the Heinsberg district, some of whom were treated with intensive care at the University Hospital Aachen, an increase in risk was found in patients with obesity (overweight) in addition to the known risk factors for a severe course. Lymphocytopenia was not observed in this small cohort of patients, but the severely ill patients all exhibited significant leukocytosis.

As in adults, symptoms in children include cough and fever, as well as gastrointestinal problems with or without diarrhea. In most cases, the disease progresses without symptoms or with only mild symptoms. In children with pre-existing conditions of the respiratory or cardiac system, infants and young children, severe courses requiring intensive medical treatment have been reported. MIS-C syndrome has been observed in children in several countries.