Do infected people release coronavirus without symptoms?
Can a new coronavirus infection spread to infected people without symptoms of disease. Mathematical models say so. It is well known that people with mild symptoms can carry a high viral load and be viral spreaders.
Until recently, it was thought that the SARS-CoV-2 virus was mostly spread by people who already had symptoms. But empirical data put this hypothesis into question - both the study of real cases and mathematical modeling say that the opposite can be true.
Despite all precautions, the epidemic is spreading and gaining momentum. Many have begun to wonder - maybe asymptomatic virus carriers are spreading the infection too? This would explain the difficulty in containing it: when a person has no symptoms, the person concerned is more tempted not to follow the safety rules of the epidemic, and medical staff have less opportunity to identify and isolate the patient.
The Internet is flooded with all kinds of information that confuse the number of infections from asymptomatic carriers (this is the indicator in question) with the number of people who have the disease in principle with little or no symptoms. It comes to the assertion that 50-75% of patients do not show significant symptoms.
No epidemiological data are available for such claims. We don't know how many people actually have the disease asymptomatically. We can only judge this indicator by specific cases or build mathematical models that predict this number. But judging by the experts in an interview for CNN, the index is probably higher than we thought.
In Massachusetts, for example, patients reported that at least 82 of the known patients had been infected by someone who was not yet symptomatic.
Symptoms of COVID-19 The most common symptoms of a new coronavirus infection:
an increase in body temperature,
fatigue,
dryer,
dry cough. A number of patients, according to WHO, may have various pains, stuffy noses, runny nose, pharyngitis (inflammation of the mucous membrane of the throat and tonsils) or diarrhoea. These symptoms tend to develop gradually and are mildly affected. Some infected people do not develop any symptoms or feel unwell. Approximately one in six cases of COVID-19 develops severe symptoms with respiratory failure. Older persons as well as persons with existing somatic diseases such as arterial hypertension, heart disease or diabetes are more likely to develop severe symptoms. If you have a high body temperature, cough, breathing problems or mental confusion, you should consult a doctor.
On Tuesday, the director of the Institute of Medical Virology in Frankfurt, Professor Sandra Ciesek, tested the passengers of one plane that flew from Israel to Germany, a total of 24 people. Seven of them had a positive coronavirus test. Four of them had no symptoms, but the viral load, calculated from smears taken from patients without symptoms, was higher than three with characteristic symptoms. (Viral load, a measure of the severity of a viral infection, is calculated by estimating the number of viral particles in a certain amount of body fluid, in this case the lung secret. A higher load means that someone is more likely to spread the infection to other people). The results of the study have not yet been officially published, but they have been posted online, which, however, is typical for articles on the new coronavirus available at the moment, as the process of pre-publication of the official review takes a long time.
Another study not yet published, but released on MedRxiv presents mathematical models to predict the number of people infected by people without symptoms. It uses January and February epidemiological data from the Chinese city of Tianjin and Singapore and tells us that many people were infected at the presymptomatic stage. On Saturday, a joint Belgian-Danish study showed that 48% to 66% of 91 people infected in Singapore had picked up the virus from people with no symptoms. For the Tianjin (135 cases), this is the path of infection typical of 62-77% of those infected.
Canadian, Danish and Singaporean researchers, based on the same data, suggested that the average infection was further transmitted 2.55-2.87 days before symptoms appeared.
The American Centers for Disease Control and Prevention (CDC) are still of the opinion that the disease is mostly spread by people with symptoms.
So far, it is useful to know that people with moderate manifestation of the disease (there are) can accurately have a high viral load, which makes the COVID-19 epidemic different from the SARS outbreak in 2002-2003, when the pathogen was spread by patients with a pronounced clinical picture.