As sweeping efforts to contain theCOVID-19 pandemic go into effect around the globe, researchers are starting toget hints of just when patients are most contagious.

People infected with the SARS-CoV-2virus, which causes the disease, may test positive for the virus both beforeand after they have symptoms. But a new study of nine people who contracted thevirus in Germany suggests that people are mainly contagious before they havesymptoms and in the first week of the disease.

Infectious viruses were isolated fromabout 17 percent of nose and throat swabs and more than 83 percent of phlegmsamples during that first week, researchers report March 8 in a study posted atmedRxiv.org.

Patients produced thousands to millionsof viruses in their noses and throats, about 1,000 times as much virus as producedin SARS patients, Clemens Wendtner, director of infectious disease and tropicalmedicine at Munich Clinic Schwabing, a teaching hospital, and his colleaguesfound. That heavy load of viruses may help explain why the new coronavirus isso infectious.

Headlines and summaries of the latest Science News articles, delivered to your inbox

Scientists identified these nine peoplesome time after they had been exposed to the coronavirus, so researchers dontknow for sure when exactly people begin giving off virus. After the eighth dayof symptoms, however, the researchers could still detect the viruss geneticmaterial, RNA, but they could no longer find infectious viruses. Thats anindication that antibodies that the bodys immune system makes against SARS-CoV-2are killing viruses that get out of cells, Wendtner says.

The study brings an important point tolight; finding RNA or pieces of a virus in a swab or sample is no guaranteethat the virus is live, or infectious, says Ali Khan, dean of the College ofPublic Health at the University of Nebraska Medical Center in Omaha. Some ofit is discouraging news because when you are mildly [ill] or just [getting]sick, youre putting out a whole lot of virus, which explains why were seeingso much transmission within our communities, says Kahn, was not involved in thestudy.

But theres encouraging news, too.Plummeting numbers of infectious virus after antibody production turns onmeans that after about 10 days or so, youre not likely to be infecting otherpeople, Khan says. Other studies also suggest that people with very mild orasymptomatic infections dont shed as much virus and arent as likely to infectother people as people with more severe cases, he says.

Wendtner and colleagues put the nine patientsthrough tests every morning during their hospital stay, collecting blood,urine, stool, nasal and throat swabs and asking the people to cough up sputum,or phlegm. We were learning with the patients because we did not know whenwould be the best and safest time to discharge them, Wendtner says.

The high levels of virus shedding fromthe nose and throat happened very early in infection by the time of testing,most patients upper airway virus production had already peaked. As theinfection progresses, the virus moves deeper into the lungs, the findingssuggest.

The team never found evidence of thevirus in blood or urine and has stopped collecting those samples from a secondwave of 23 COVID-19 patients now being treated at the hospital. Researchersdid detect viral RNA in feces, but no infectious virus there. That suggeststhat the virus isnt spread through stool, an unknown until now.

All nine patients are employees ofWebasto, an auto supplier in Stockdorf. They caught the virus from a malecoworker, who became known as Patient 1. He originally got the virus from abusiness colleague from Shanghai who came to Germany in January for aseries of meetings (SN: 1/31/20). BothPatient 1 and his Shanghai colleague transmitted the virus before developingsymptoms, the first documented cases of asymptomatic spread.

As health officials tested otheremployees of the company, they found the study participants and placed them inisolation at the Munich clinic. In one case, Patient 1 sneezed during a meetingwith one person, Wendtner says. That was enough for infection. In othercases, they had simple business meetings, sitting together for 60 minutes, 90minutes [at a table or] in front of a computer, with no physical contact justone handshake, thats all, Wendtner says. The infectivity is quite high.

Most had coughs, but only two developeda fever, the most common symptom reported in other studies. Most symptoms were mild and one person neverdeveloped any at all. One patient developed severe pneumonia.

Two of the nine had runny noses,previously reported as a rare symptom of COVID-19. Another four had stuffynoses and reported that they couldnt smell or taste anything. In all of ourpatients, it cleared up, but it was a little bit annoying for two weeks or so,Wendtner says. They could order anything they wanted [to eat], but [if] youcant taste it, it doesnt matter.

A temporary lack of smell or taste also affectedsome SARS patients in 2003, he says. That symptom may indicate that in additionto causing swelling in the nose, the virus may infect nerve cells responsiblefor identifying odors, he says.

Patients in the study started makingantibodies against the virus about six to 12 days after symptoms started. Onceantibody production kicked in, researchers still found high levels of viral RNAin phlegm and in nose and throat swabs, but patients were no longer giving offinfectious virus.

The early and extreme contagiousness of the virus tell us that gatherings of people should be avoided, Wendtner says. But the results also may suggest that isolation periods could be shorter for people who have RNA but no virus. Researchers thought that because tests could still detect RNA for up to weeks after symptoms had cleared (SN: 2/28/20), patients were infectious for that long. Most patients are not released from the hospital until two separate tests within 24 hours come back negative, Wendtner says.

But Wendtner isnt suggesting letting people out of quarantine before their two weeks are up. Fourteen days is safe, and you have to keep it simple, Wendtner says. Maybe its safe 10 days after symptoms start, but you have to prove they have those neutralizing antibodies. Tests for the antibodies, however, are not widely available.

The reliable science journalism you count on is expensive. It takes professional reporters, editors, fact checkers, designers and digital producers to make sureScience Newsreflects the depth and breadth of science.We need your financial support to make it happen every contribution makes a difference.

Originally posted here:
Coronavirus is most contagious before and during the first week of symptoms - Science News

Comments are closed.