Scientists identify longest COVID infection, at 505 days

longest COVID infection, occult covid
© Milton Cogheil

After a study of immunocompromised patients, UK researchers found the longest COVID infection case to be 505 days

The team, from King’s College London and Guy’s and St Thomas’ NHS Foundation Trust, wanted to figure out how COVID mutates in people who are immunocompromised.

Researchers say the longest COVID infection case is now 505 days, as of this study. The previous longest documented case is thought to be 335 days.

They worked with nine patients, who were highly vulnerable to the disease due to recent organ transplants, HIV, cancer or medical treatment for other health conditions. This analysis was conducted early in the pandemic, from March 2020 to December 2021.

Dr Gaia Nebbia, co-author, said: “Immunocompromised patients with persistent infection have poor outcomes, and new treatment strategies are urgently needed to clear their infection. This may also prevent the emergence of variants.”

Tragically, only five of the nine patients survived.

Among this group, 73 days was the average length of COVID infection – but two patients experienced the virus for more than a year.

How do mutations develop in immunocompromised COVID patients?

Mutations are different to fully fledged variants. Mutations are the minute changes that make-up a new variant, while the virus tries out various adaptions to see how it can become more infectious and more fatal.

The findings, presented to the European Congress of Clinical Microbiology & Infectious Diseases, suggest that five of the nine patients developed atleast one mutation that was associated with variants of concern – such as Alpha, Delta or Omicron.

The team found that some of the patients developed multiple mutations, which would later be associated with the three variants mentioned before. In one patient, there were ten mutations which would later be seen in Alpha, Gamma and Omicron.

Dr Luke Blagdon Snell, first author, said: “Some of these variants transmit more easily between people, cause more severe disease, or make the vaccines less effective. One theory is that these viral variants evolve in individuals whose immune systems are weakened from illness or medical treatments like chemotherapy, who can have persistent infection with SARS-CoV-2.

“We wanted to investigate which mutations arise, and if variants evolve, in these people with persistent infection.”

It seems that the longest COVID infection cases, especially in immunocompromised people, can lead to mutations that could later become globally dominant.

Report also documents known case of ‘occult’ COVID infection

The team also found details of one of the first occult COVID infections. Fortunately, this infection has nothing to do with ghosts. Unfortunately, the reality is more sobering for healthcare professionals and patients across the globe.

Occult infections happen when a patient was thought to have cleared the virus – including testing negative – they continue to have an ongoing infection. This is completely different to Long COVID, which is a separate, complex issue – with recent studies finding that women are more likely to exhibit symptoms.

The authors, reflecting on this, said: “This has been described with other viruses such as those that cause Ebola or hepatitis B and is different to long Covid where the virus is generally thought to be cleared from the body but symptoms persist.

“The patient was symptomatic and tested positive for Covid before recovering. They then tested negative several times before developing Covid symptoms again several months later. A PCR test was positive and genome sequencing of the virus at this point showed the infection was caused by the Alpha variant, which had by then been eliminated from the UK, suggesting the virus had been present in the body ever since the initial infection but remained undetected.”


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