A new case study published in the journal Cell reveals that a 71-year-old hospital patient diagnosed with COVID-19 in Kirkland, Washington, who also had leukemia, shed infectious particles of the respiratory virus for at least 70 days without showing any symptoms of the disease.

According to the study, the patient continued to shed infectious particles of SARS-CoV-2, the virus that causes COVID-19, 70 days after her diagnosis. More than 100 days after her initial diagnosis, the woman was still testing positive for COVID-19, which indicates that her body still contained trace amounts of genetic material from the novel coronavirus.

"We think that at least up to day 70, this patient would have been able to spread the virus to others," Vincent Munster, a virologist at the US National Institute of Allergy and Infectious Diseases who was involved in the study, told the Business Insider.

"This was something that we expected might happen, but it had never been reported before," Munster added.

The researchers came to their conclusions by studying samples collected from the patient’s upper respiratory tract. According to the study, the patient’s 70-day period of infectiousness is the longest span of infectious shedding yet seen in an asymptomatic COVID-19 patient. 

The longest-known infectious shedding span for a symptomatic person is 61 days.

Researchers believe that the woman remained infectious for so long because her weakened immune system was unable to generate a substantial amount of antibodies to fight the virus. In fact, blood tests indicated that the patient’s body was never able to make such antibodies. 

At one point, she was treated with convalescent plasma, a technique in which doctors isolate antibodies in the plasma of survivors of the novel coronavirus and inject those antibodies into sick patients. Plasma is the liquid component of blood.

However, the treatment did not have an effect on the patient due to her low concentration of antibodies. Despite this, she never showed any symptoms of COVID-19.

"At the time we started this study, we really didn't know much about the duration of virus shedding," Munster told Cell Press.

"As this virus continues to spread, more people with a range of immunosuppressing disorders will become infected, and it's important to understand how SARS-CoV-2 behaves in these populations."

The latest data by Worldometer reveals that there have been more than 10 million cases of COVID-19 in the US and over 244,000 COVID-19-related deaths.