With over 500,000 confirmed cases of Covid-19 infection worldwide, there is one clear fact about SARS-CoV-2, that this new strain of corona virus has the potential to spread very strongly.
Now, a series of studies are slowly revealing the mystery that creates the level of infection of SARS-CoV-2. When is a person with Covid-19 most likely to spread the virus to others?
While we know that older people over the age of 60, people with underlying medical conditions, such as cardiovascular disease, diabetes, people with weakened immune systems, are the most vulnerable to the virus. But there were also cases of Covid-19 knocking out healthy adults, putting them in a critical state of pneumonia.
In addition, the virus can also infect a person without causing any symptoms. These first cases were confirmed in China in January, in a study published in the journal Science China Life Science. Although scientists did not know the prevalence of Covid-19 at the time, it did not show how widespread the symptoms were.
A study posted on Science magazine Last week analyzed the evolution of the Covid-19 epidemic in 375 cities in China from January 10 – when the disease broke out until January 23 – when preventive measures like travel restrictions were imposed. use.
In it, Dr. Jeffrey Shaman at Columbia University and his colleagues came to the conclusion that 86% of Covid-19 infections in China were asymptomatic or showed only very mild symptoms. .
Data of foreign nationals evacuated from Wuhan also give a similar rate of virus infections but no symptoms or mild symptoms.
Research shows that asymptomatic cases make a major contribution to the spread of SARS-CoV-2 virus in China, before blockade and travel restrictions are implemented.
Although the probability of infecting others with asymptomatic Covid-19 cases is only 55% of that for symptomatic patients, research shows that they are responsible for 79% of new Covid- 19 during this time.
The reason may be because the asymptomatic cases or mild symptoms are actually more common. And more likely they are still out.
If someone has Covid-19 infection with mild symptoms, Dr. Shaman thinks most of them will still go to work or hang out normally. “These people are the drivers of the disease and they are the facilitators of the spread of the disease“he said.
A project in Italy Also found many cases of asymptomatic Covid-19 infection. When the test was rolled out to people in a town called Vo – one of the places most heavily affected by the epidemic in Italy – 60% of those who tested positive had reported that they were not. have symptoms.
This is lower than the number found in China, but they are all at the same high level, Dr. Shaman said. “It is 1/10 in some societies, compared to 1/5 in other societies, but overall, you will probably have a much greater degree of confirmed cases.“he said.
According to the Centers for Disease Control and Prevention (CDC)Most people with Covid-19 have mild symptoms and progress slowly.
While people often hear that cough, fever, shortness of breath and fatigue may be signs of Covid-19, there are still other symptoms of the disease including runny or stuffy nose, sore throat, and pain. headache, muscle aches, diarrhea, nausea and vomiting.
Among confirmed confirmed infections, 19% of patients will progress to a serious or critical condition, usually pneumonia. Mortality varies depending on a number of factors, such as the average age of the population, the state of the national health care system and the extent to which minor cases are identified and included. statistical.
A study posted on Nature Medicine magazine Last week it was estimated that 1.4% of symptomatic Covid-19 cases in Wuhan had died. Rarely do children infected with the new corona virus develop serious or critical conditions. However, the irony is that healthy, mature people can still have severe pneumonia because of it.
“There are some young people who eventually need special care“, British government chief medical adviser Chris Whitty announced in a brief meeting on March 19.
According to a study posted on Annals of Internal Medicine, When someone is infected with Covid-19, their incubation period usually lasts from 2 to 14 days. Half of all cases had symptoms before the 6th day.
However, these figures were calculated using a confirmed 181 case study of Covid-19 infection, which means that it does not take into account very small or asymptomatic cases.
It is worth mentioning that a person infected with Covid-19 can begin to infect the virus to others, even if they have not manifested any symptoms. A study in China shows that the infection began about 2.5 days before the symptoms appear on the infected person, and reached its peak within the previous 15 hours.
But while we know that the SARS-CoV-2 virus is spread through coughs and sneezes of an infected person, how do people who have no symptoms, no coughs, or sneezes spread the disease to others?
People with Covid-19 with mild or asymptomatic symptoms may still have very high viral loads in their upper respiratory tract. That is, they can spread the virus through spitting, touching the mouth or nose and then touching the surfaces. Or they can spread the disease by talking, not necessarily coughing or sneezing.
As symptoms develop, a person’s viral load decreases and they become less infectious. However, people seemed to continue spreading the virus for about two weeks after they recovered from Covid-19, the virus appeared both in saliva. and their poop. This means that even if a person has no symptoms, they can still pass the virus on to others.
Airborne droplets are likely to be Covid-19’s main route of infection, but virus-contaminated surfaces may also contribute. Medical advice often states that the virus can survive for about 2 hours on surfaces, biologist William Keevil at the University of Southampton, UK.
But a study published in the journal New England Journal of Medicine Last week showed that this is a severity underestimation. SARS-CoV-2 virus can survive up to 14 hours on the surface of cardboard boxes and up to 3 days on plastic and stainless steel surfaces. It can also hover around in the air for at least 3 hours, inside aeresol droplets.
“The multi-day survival of new corona virus on touching surfaces is a hygiene risk.”, Keevil said. “It is difficult to avoid touching [vật hoặc bề mặt bị ô nhiễm] like door handles and push panels, bedside and stair railings, touch screens, etc. “.
Some studies also show evidence that SARS-CoV-2 virus can be transmitted from a patient’s stool, Elizabeth Halloran at the University of Washington said. This reinforces the importance of hand washing.
Keevil recommends washing your hands often, scrubbing with soap for at least 20 seconds or using an alcohol-based dry hand wash. You also need to avoid touching your eyes, nose and mouth.
All of these studies make it clear that advising only people with coughs or fever, even their families to quarantine themselves, will not prevent the spread of corona virus. That’s because of its monstrous ability to cause disease and hidden disease.
Some people infected with the virus have only mild symptoms. And they can even push the probability of infection to its peak before they even realize they are sick.