COVID most contagious two days before symptoms show
Posted January 11, 2021 5:36 p.m. EST
Updated January 11, 2021 6:54 p.m. EST
A new study from the Centers for Disease Control and Prevention found that 59% of all COVID cases are spread from people without symptoms. The study says 35% of cases come from people who are pre-symptomatic, meaning they don’t have symptoms yet, but eventually will develop them. Another 24% is estimated to be spread from asymptomatic people – those who carry the disease but never show signs of it.
“We have learned that people without symptoms can definitely transmit disease. We have seen that,” said North Carolina health director Dr. Betsey Tilson.
Scientists have said since the beginning of the pandemic that the virus is spread through droplets, but recent research shows that doesn’t have to be from a sneeze or cough from an infected person. Any droplets, even from talking or close contact, can spread the virus, and experts say people are most contagious about two days before they start showing symptoms.
“The reason that’s scary is because that’s when your virus level is the highest and that’s when you’re most infectious," said Dr. Krutika Kuppalli, an infectious disease expert at the Medical University of South Carolina in Charleston who has been on the front lines of treating patients and working to understand how COVID spreads.
Another new study, published in Journal of the American Medical Society Internal Medicine, indicates these asymptomatic people with COVID carry as much virus in their nose, throat and lungs as people with symptoms. They can also carry and spread it for almost as long.
“So even you’re less likely to transmit the disease, if more people are asymptomatic, it still can be contributing to that overall population spread,” Tilson said.
Typhoid Mary: Infamous superspreader
The first asymptomatic disease carrier in the English-speaking world was a woman with a likely familiar nickname: Typhoid Mary.
Judith Walzer Leavitt wrote a book about the famous disease spreader called Typhoid Mary: Captive to the Public's Health.
“Mary Mallon was an Irish immigrant who came to this country in the 1880s as a teenager,” she explained in an interview with WRAL. “And she started working, as most single Irish women did at that moment in history, as a domestic worker, and she learned that she was a very good cook. So being a cook was the highest paid of the domestic jobs, and so she was very happy to have it. She did very well at it. She had a terrific reputation She cooked for a lot of the wealthier families on the East Coast, in New York mostly, but she would go with them to their summer homes and whatnot.”
After several people in a home where she was working in Oyster Bay, New York, became sick with Typhoid fever in 1907, an investigator was hired to find out what caused the illness.
“They couldn’t find the usual culprits, which were contaminated water or food or seafood, and so they began looking for another source,” Leavitt explained.
George Soper was hired to figure out where the disease had come from and remembered an article he had read about a theory that asymptomatic people still being able to transmit disease.
In what may be our country’s first effort at contact tracing, Soper “tested everybody in the household and asked about everybody who had come and gone around the time of this outbreak.” After determining that nobody else had been the source of the disease, Soper start looking for Mary Mallon. “By the time he was doing his investigation, she had left the family. So he had to trace her back down to Manhattan where she was working for a different family.”
When Soper located Mallon in the new kitchen where she was working and explained he needed a sample of her stool and urine to test her as a potential typhoid spreader, Mallon was disbelieving and irate, threatening him with a carving fork.
Soper looked into her background and found that of the eight families she had worked with, seven had reported typhoid cases. When she was finally located, she was arrested by the New York Health Department as a threat to public health. She was isolated on North Brother Island, in the East River off Manhattan.
“She was first held from 1907 to 1910, and then the judge in that case said that the health department had every right to take her back, that she was a menace,” Leavitt explained. “They called her ‘a menace to public health,’ and the health department has a right to isolate people they think are dangerous.”
Eventually it was agreed that Mallon could leave the island, with the stipulation that not go back to being a cook. The judge made Mallon “sign a piece of paper saying she wouldn’t cook again,” Leavitt said. “But she still didn’t really understand that she could be transmitting the disease. For four years she kept out of the kitchen,” but then returned to the profession.
When she was caught for the second time, she was sent back to enforced quarantine on North Brother Island, this time for 23 years, from 1915 to her death in 1938. Ironically, Mallon's job on the island was working in a bacteriology lab, where she looked at slides under a microscope and determined whether samples were tuberculosis or not. The island was mostly used as a quaratine site for suspected TB patients.
Tilson said a similarity exists between Mary Mallon and how we’re seeing COVID be transmitted right now.
“Talking about Typhoid Mary, one interesting thing we’re learning about this virus, is, unlike with flu where it seems to be spread a little bit more equitably … Certain individuals seem to spread more than others, so you do see these sort of super spreaders,” she said.
Kuppali says another reason why asymptomatic spread could be so high is because people may be less likely to stick to health precautions like the 3 Ws or staying at home when they don’t feel bad or don’t have symptoms.
“So if you’re feeling okay and you’re out and about, and your virus level is at the highest and you’re not protecting others from you by wearing your mask, that’s how the virus can spread,” she said.
Leavitt sees other lessons that Mary Mallon and the case of Typhoid Mary can teach us in the modern day.
"In Mary Mallon’s case, she thought that there were two kinds of justice in America – one for the rich and one for the poor. And she knew that she was getting the raw end of the stick right from the start. And I think a lot of people know that today too. So I think we really have to work on creating policies that are just, equally applied.”
Leavitt says creating equitable health systems and public policies would go a long way in easing the resistance to masks and vaccinations that we’re seeing now during COVID.
“If we had that,” she said, “people would be more likely to cooperate, and cooperation is one of the things we really need to affect a good public health policy.”