Longest COVID-19 infection reported: Patient had virus for 505 days.

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The patient had a weakened immune system that prevented them from clearing the infection.

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A patient in the United Kingdom was infected with COVID-19 for a record 505 days, or more than 16 months, before their death, according to a new report.

The case is the longest-known continuous infection with COVID-19 reported to date, surpassing the previous record of 335 days, according to the researchers.

The patient had a weakened immune system that prevented them from clearing the infection properly. 

"These were throat swab tests that were positive each time. The patient never had a negative test," study first author Dr. Luke Blagdon Snell, of the Department of Infection at Guy's and St Thomas' NHS Foundation Trust in London, told the BBC. "And we can tell it was one continuous infection because the genetic signature of it — the information we got from sequencing the viral genome — was unique and constant in that patient."

The patient's case was presented this week at the European Congress of Clinical Microbiology & Infectious Diseases in Lisbon, Portugal. The case was part of a study of nine patients with weakened immune systems and prolonged COVID-19 infections. The study has not yet been published in a peer-reviewed journal.

Although such lengthy infections with COVID-19 are rare, it is important to study them because they could give rise to new variants of SARS-CoV-2, the virus that causes COVID-19, the authors wrote in the study. When a person is infected with SARS-CoV-2 for a long time, it gives the virus many chances to develop mutations to evade the immune system.

Indeed, the authors found that, in five of the nine patients, the virus developed at least one mutation found in  coronavirus variants of concern, including the alpha and beta variants, according to the study abstract.

"Immunocompromised patients with persistent [COVID-19] infection have poor outcomes, and new treatment strategies are urgently needed to clear their infection," study co-author Dr. Gaia Nebbia, an infectious disease specialist at Guy's and St Thomas' NHS Foundation Trust, said in a statement. "This may also prevent the emergence of variants."

Originally published on Live Science. 

Rachael Rettner
Rachael Rettner
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.