Washington woman who had Covid-19 shed infectious virus particles for 70 days, reveals unusual case study
The 71-year-old was infected with the coronavirus for at least 105 days while showing no symptoms the entire time
While scientists are still trying to understand Covid-19 and how it affects people, a research team now reports the unusual case of a woman with coronavirus who shed infectious virus particles for at least 70 days, which means that she was contagious during that entire time. This is despite the fact the 71-year-old from Washington state never showed symptoms of the disease, according to the authors.
The patient from Kirkland had chronic lymphocytic leukemia due to which she was immunocompromised, and had a low antibody count. She was found to be infected with the virus when she was screened after being admitted to the hospital for severe anemia and her doctors recognized that she had been a resident of a rehabilitation facility experiencing a large outbreak. The analysis reveals that she was infected with the coronavirus for at least 105 days, and was infectious for at least 70 days, while remaining asymptomatic the entire time.
According to senior author Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases (NIAID), this is the longest case of anyone being actively infected with SARS-CoV-2 (the virus that causes Covid-19) while remaining asymptomatic. “We’ve seen similar cases with influenza and with Middle East respiratory syndrome, which is also caused by a coronavirus. We expect to see more reports like ours coming out in the future,” he wrote in the analysis published in the journal Cell.
The findings contradict guidelines from the US Centers for Disease Control and Prevention (CDC), which suggests that immunocompromised people with Covid-19 are likely not infectious after 20 days.
During a disease outbreak such as the Covid-19 crisis, understanding how long people can remain actively infected is important, because it provides new details about a disease and a virus that are still not well understood and informs public health decisions, say experts. “At the time we started this study, we didn’t know much about the duration of virus shedding. 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,” explains Munster.
What did the research team find?
While the exact time when the patient got infected with Covid-19 is unknown, the exposure likely occurred in the long-term care facility where she resided between February 19-25, just shortly before a large Covid-19 outbreak was identified in that facility on February 28.
Munster was contacted in April by infectious disease specialist Francis Riedo, a study co-author, about the patient. Riedo’s patient had many positive tests for the virus for weeks, and he wanted to know if she was still shedding virus. Munster’s lab at NIAID's Rocky Mountain Laboratories in Hamilton, Montana, began studying samples that were regularly collected from the patient’s upper respiratory tract. They found that the infectious virus continued to be present for 70 days after the first positive test, and the woman did not fully clear the virus until after day 105. “This was something that we expected might happen, but it had never been reported before,” says Munster.
The authors believe the patient remained infectious for so long because her compromised immune system never allowed her to mount a response. Blood tests showed that her body was never able to make antibodies. At one point she was treated with convalescent plasma, but the investigators do not think the treatment had an effect because of its low concentration of antibodies. “The infection was not cleared after a first treatment with convalescent plasma, suggesting a limited impact on SARS-CoV-2 in the upper respiratory tract within this patient. Several weeks after a second convalescent plasma transfusion, SARS-CoV-2 RNA was no longer detected,” the findings state.
The team performed deep sequencing on all the virus samples obtained from the patient to see how the virus might have changed throughout the woman’s infection. Samples collected at various times displayed different dominant gene variants. However, the researchers do not think that these mutations played a role in how long the virus persisted, because they saw no evidence of natural selection. “Selection would have been implicated if one of the variants had appeared to provide the virus with a survival benefit and had become the dominant variant, but none of them did,” they explain. The investigators also tested whether or not the mutations affected the ability or speed of the virus to replicate and found no differences.
While this report focuses on the long-term shedding of one immunocompromised patient, an estimated 3 million people in the US have some form of the immunocompromising condition, the researchers emphasize. According to them, the study findings indicate that certain immunocompromised patients may shed infectious virus for longer durations than previously recognized. “Although it is difficult to extrapolate from a single patient, our data suggest that long-term shedding of infectious virus may be a concern in certain immunocompromised patients. Given that immunocompromised patients could have prolonged shedding and may not have typical symptoms of Covid-19, symptom-based strategies for testing patients and discontinuing transmission-based precautions, as recommended by the CDC, may fail to detect whether certain patients are shedding infectious virus,” they caution.
The investigators suggest that “understanding the mechanism of virus persistence and eventual clearance” will be essential to providing appropriate treatment and preventing transmission of SARS-CoV-2, as persistent infection and prolonged shedding of infectious coronavirus may occur more frequently. “Identification of additional cases of persistent infection and long-term shedding of infectious virus are needed so the infection dynamics can be studied in this diverse population in more detail,” they conclude.