She refused to give stool samples to authorities and continued to spread the bacteria via her unsanitary ways until she was caught and quarantined twice for a total of 26 years, dying alone without friends.

While no one wants to think of themselves as a super spreader of Covid-19, a new study has given support to the idea that "silent transmission" -- the spread of virus by someone with no obvious symptoms -- could be responsible for half of all novel coronavirus cases in the United States.

Transmission via people with no symptoms, or during the few days before symptoms are apparent, is a primary driver of Covid-19 spread, the study, published Monday in the Proceedings of the National Academy of Sciences, found.

More than one-third of silent infections would need to be identified and isolated to suppress a future outbreak, the study estimated.

According to Tuesday morning's Johns Hopkins University data, 31 states are reporting higher rates of new Covid-19 cases this week compared to last week.

"So it's a serious situation that we have to address immediately."

Asymptomatic or presymptomatic spread

Alison Galvani, director of Yale University's Center for Infectious Disease Modeling and Analysis, and colleagues used coronavirus transmission models to determine the extent to which silent transmission contributes to the spread of Covid-19.

They based the study on existing research, which indicates asymptomatic infections account for 17.9% to 30.8% of all infections.

Assuming 17.9% of cases are asymptomatic, the team found that presymptomatic people would account for 48% of transmission, and asymptomatic people would account for 3.4% of transmission.

If 30.8% of cases are asymptomatic, they found that presymptomatic people would be responsible for 47% of transmitted cases and asymptomatic people would account for 6.6% of transmission, respectively.

The model assumes Covid-19 may be most contagious during the presymptomatic stage, which is uncommon for a respiratory infection.