A London hospital patient tested positive for COVID-19 for 505 days before he died, according to evidence presented this week at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) in Lisbon, Portugal.
In addition to representing the longest known COVID-19 infection, this extraordinary case highlights the ability of the SARS-CoV-2 virus to persist in immunocompromised patients, where it can mutate and adapt.
There are currently three main theories about how new variants of the virus arise, one of which posits that the pathogen can remain and evolve in patients with compromised immune systems, such as those undergoing treatment for cancer or HIV. Another hypothesis states that the virus changes as mutations accumulate during the chain of infections from person to person, while the third theory suggests that adaptations occur as the pathogen jumps between people and animals.
The researchers analyzed genetic changes in the SARS-CoV-2 virus in immunocompromised patients who tested positive for at least eight continuous weeks. Between March 2020 and December 2021, the team identified nine individuals in London who met these criteria, four of whom subsequently died.
Patients tested positive for an average of 73 days, with the shortest infection lasting 56 days and the longest 505 days. One patient – who remains alive – carried the virus for 412 days at the time of his last check-up in early 2022 and could set a new record by the time his next check-up arrives.
Importantly, the researchers found that the SARS-CoV-2 virus developed mutations associated with worrisome variants in five of the nine patients. This includes mutations that change the nature of the spike protein the virus uses to enter cells and that have given rise to new variants such as Alpha, Delta and Omicron.
A patient’s virus contained ten mutations that would later appear separately in some of these new variants. In a statement, study author Luke Blagdon Snell explained that “this provides evidence that mutations found in variants of concern arise in immunocompromised patients and therefore supports the idea that new variants of the virus can develop in immunocompromised individuals.” .
“It is important to note, however, that none of the individuals in our work developed new variants that became generalized variants of concern,” he said.
“Furthermore, while this work shows that variants can arise in immunocompromised individuals, it remains to be seen whether earlier variants of concern, such as Alpha, Delta, and Omicron, arose this way.”
The researchers also report the detection of the first known case of an occult COVID-19 infection, in which the virus persisted in a patient thought to have shed the pathogen. The person in question was initially infected with the Alpha variant before recovering and testing negative for the virus – only to test positive again after developing symptoms several months later.
Interestingly, this second infection was also caused by the Alpha strain, despite the variant having already been eliminated from the UK by this time. Based on this observation, the researchers say the virus must have remained in the patient’s body undetected since the initial infection.
Earlier this week, doctors reported the fastest known COVID-19 reinfection after a 31-year-old healthcare worker caught the illness twice in the space of 20 days. Collectively, findings like these are helping scientists understand how the virus adapts to avoid vaccines and become more infectious.