An immunocompromised leukaemia patient was infected with the SARS-CoV-2 virus for at least 105 days, and was infectious up to 70 days after first testing positive for the virus, while remaining asymptomatic the entire time, US doctors have reported.
The case underlines the importance of immune system reactions to the virus in causing severe illness, the researchers suggest. The weakened immune system led to the patient being infected for a long period without symptoms, they report.
Analysis was conducted by the National Institute of Allergy and Infectious Diseases and reported in the latest edition of the journal Cell.
The 71-year-old woman, who had chronic lymphocytic leukaemia and acquired hypogammaglobulinemia, was admitted to hospital for severe anaemia. Doctors recognised she had been a resident of a rehabilitation facility that had experienced a large outbreak, and so was tested for SARS-CoV-2 viral RNA, and found to be positive on 2nd March 2020.
Senior author Dr Vincent Munster was contacted in April by study co-author Francis Riedo, an infectious diseases expert, about a patient in Kirkland, Washington, who had had several positive PCR tests over a number of weeks.
Dr Munster studied samples that were regularly collected with nasopharyngeal and oropharyngeal swabs. He found that infectious virus could be isolated from the swabs up to 70 days after the first positive test, and that she was still testing positive for viral RNA on day 105.
The investigation team believes the patient continued shedding virus for so long because her compromised immune system did not allow her to mount a response, with blood tests confirming that her body was unable to make antibodies. She never developed symptomatic COVID-19.
She was treated with convalescent plasma, but Dr Munster says he doubts the treatment had an effect because of its low concentration of antibodies.
Deep sequencing was carried out on the virus samples obtained from the patient to see how the virus had changed over the course of the infection. While they found that samples collected displayed different dominant gene variants, they do not believe the mutations played a role in how long the virus persisted as there was no evidence of natural selection.
Dr Munster said: “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.”
Avanzato VA, Matson MJ, Seifert SN, Pryce R, Williamson BN, Anzick SL, Barbian K, Judson SD, Fischer ER, Martens C, Bowden TA, de Wit E, Riedo FX, Munster VJ (2020) “Case Study: Prolonged infectious SARS-CoV-2 shedding from an asymptomatic immunocompromised cancer patient.” Cell, doi: 10.1016/j.cell.2020.10.049