Researchers Analyze Long-term Symptoms of COVID-19, Pneumonia, Flu

In July 2021, 9.4% of patients with COVID-19 sought treatment for symptoms that may indicate long COVID-19. According to research published in Epic Research, COVID-19 may not be the only respiratory infection that can result in chronic symptoms afterward.

The study authors looked at long-lasting symptoms after 3 viral respiratory diseases: COVID-19, influenza, and viral pneumonia. However, they also analyzed symptoms reported before the acute episodes of those diseases.

“We felt like there would be a certain group of people who ended up having a visit to the doctor for certain symptoms, so there would be a general rate of these visits for these types of symptoms that we were looking for,” said study author Jeff Trinkl, MD, director of clinical informatics at Epic. “That would not necessarily be related to 1 of the diagnoses that we were looking for—COVID, influenza, and other respiratory illnesses.”

The sample population consisted of 3 groups:

• Patients diagnosed with COVID-19 between January 1, 2020, and July 1, 2021
• Patients diagnosed with a non-COVID, non-influenza viral pneumonia between January 1, 2018, and July 1, 2019
• Patients diagnosed with influenza between January 1, 2018, and July 1, 2019.

Among these groups, the authors compared the rates of new symptoms prior to infection, and new long-term symptoms after infection.

The former group consisted of patients who sought treatment for a novel long-term symptom between 28 and 180 days prior to infection, and the latter included patients who did not report having a specific long-term symptom prior to infection, but sought treatment for that same symptom between 28 and 180 days after infection.

Following COVID-19 or viral pneumonia infection, an additional 3.7% of patients reported new long-term symptoms. Meanwhile, an additional 1.5% of patients who were infected with influenza reported new long-term symptoms.

Patients who had a respiratory infection requiring hospitalization sought treatment at higher rates overall compared with the total sample population. Of these patients, an additional 5.4% of patients with COVID-19, 6.4% of patients with influenza, and 5.2% of patients with other viral pneumonia sought treatment after infection.

“The intense focus on understanding COVID-19 has created increased awareness of chronic, post-viral symptoms around COVID-19 infections,” the authors said. “Patients who contract other respiratory infections and their doctors should also be aware of the potential for—and be prepared to treat—similar chronic symptoms.”

They also said they hope this research on long-term symptoms encourages similar conversations on long-term symptoms of other respiratory infections.

“The general conversation around long COVID has taken a lot of the attention with COVID being a pandemic,” said Eric Barkley, data scientist at Epic. “I think seeing this classification of long COVID, from this research, it's probably something that deserves to be a broader conversation that is not strictly on COVID, because we do see this pattern repeated across other infections.

The authors also noted that, due to the timing of the research, patients were not explicitly stratified by vaccination status.

This research has not yet been peer-reviewed.