TORONTO -- An American woman who previously beat cancer had COVID-19 for a year, doctors say, in a case study they hope will help scientists understand how immunocompromised people are affected by the virus.

In a pre-print report on medRxiv that has yet to be peer-reviewed entitled 鈥,鈥 researchers and doctors document their findings from treating the patient at the National Institutes of Health (NIH) in Maryland.

The patient, a 47-year-old woman who was successfully treated for lymphoma with cell therapy three years earlier, was hospitalized with COVID-19 in early 2020. In the months that followed, she became a patient of infectious disease specialist Dr. Veronique Nussenblatt at NIH.

鈥淚t took a while to be able to diagnose her,鈥 Nussenblatt said in a telephone interview with CTVNews.ca Friday, outlining how the medical team realized that their patient presented a unique case.

Nussenblatt said initial tests for the SARS-CoV-2 virus were negative, despite the patient displaying symptoms, which then led to them doing a bronchoscopy to take lower respiratory tract samples which came back positive.

鈥淪he continued to have symptoms on and off after she left the hospital,鈥 Nussenblatt said. 鈥淲hen we would test her, her test would come back positive, but a very low positive 鈥 at that time during the pandemic we knew that some people who had previously been infected with SARS-CoV-2 could have positive tests for some time after infection, especially patients who are immunocompromised.鈥

The patient, due to her past treatment for cancer, had very few 鈥淏 cells,鈥 a type of immune cell that creates antibodies to help fight off infection and help the immune system function.

Nussenblatt said that so much time had elapsed since the patient was first diagnosed with COVID-19 that as time progressed her team initially were looking for things other than a persistent infection of the coronavirus.

鈥淲e were trying to rule out other infections that she might have,鈥 she explained, adding that one train of thought was the patient had a type of pneumonia that is seen in patients after they have COVID-19 known as 鈥渃ryptogenic organizing pneumonia.鈥

To that end, the team treated the patient with steroids and noted her symptoms and her CT scans got moderately better, 鈥渂ut with no major change,鈥 Nussenblatt said.

鈥淎t that point it still wasn鈥檛 on our radar that this could be COVID-19 after so long,鈥 she said.

Things changed in March 2021.

鈥淲e realized something was wrong with our thinking when her test came back positive [in March] but a higher positive, with higher results. That to me suggested that she still had COVID-19 but it was getting more active or she had a new infection with SARS-CoV-2.鈥

At that point, Nussenblatt said, she enlisted the help of her colleague Dr. Elodie Ghedin, a molecular virologist who works at NIH and studies the genomes of the SARS-CoV-2 virus.

Ghedin and Nussenblatt did a sub-genomic PCR test on samples from the patient and found a surprise.

鈥淭he sub-genomic PCR looks for genetic material that should only be present if the virus is live, and so that told me that she actually has an active infection with SARS-CoV-2, but I didn鈥檛 know if it was the original one or a new one,鈥 Nussenblatt said. 鈥淒r. Ghedin helped determine that and sequenced the virus and found that it was actually the same virus the whole time.鈥

The patient had been infected in 2020 with one of the first versions of SARS-CoV-2 in North America, which by early 2021 was no longer circulating, the report says.

In addition, sequencing revealed two new mutations of the spike protein in the patient鈥檚 cells, which the report says 鈥渉ighlight the importance of analyzing viral evolution in protracted SARS-CoV-2 infection, especially in immunosuppressed hosts and the implication of these mutations in the emergence of viral variants.鈥

While other viruses have been known to infect immunocompromised people for longer periods of time, 鈥渨e tend not to see that with respiratory viruses,鈥 she said.

In the case of Nussenblatt鈥檚 patient, she eventually recovered and has had multiple negative COVID-19 tests since the NIH team treated her the second time around.

鈥淪he鈥檚 not 100 per cent, but she鈥檚 much better - she鈥檚 off any oxygen,鈥 Nussenblatt said, who spoke with the patient last week. 鈥淎ll the markers of an active infection are gone and she doesn鈥檛 have any symptoms anymore 鈥 all her tests are negative and the inflammatory markers in her blood have normalized.鈥

And despite having COVID-19 for a year, Nussenblatt said that to her knowledge, no one who was in close contact with the patient was affected.

Nussenblatt said the case, while rare, helps doctors ands scientists understand how the virus can affect immunocompromised people and what resources are needed to gather data on the phenomenon.

鈥淭hat was a big lesson, that immunocompromised patients can actually have SARS-CoV-2 infection for a long time,鈥 she said. 鈥淵ou know that has major implications for their treatment and also for infection control鈥 we were lucky that we had access to sub-genomic PCR testing, which not everybody has access to easily, because that really helped us determine whether or not there was a virus there.鈥

Nussenblatt said she hopes that this case study 鈥減uts the possibility of this happening on other people鈥檚 radar.鈥

鈥淲e're still learning so much,鈥 she said. 鈥滳OVID- 19 is really testing our knowledge about how to treat patients and the assumptions that we make in clinical care.鈥