Diagnosing COVID-19 vs RSV, Flu

January 25, 2024 – Amid the current wave of winter respiratory virus cases, influenza (type A and B) leads the way with the highest number of emergency room visits, followed closely by COVID-19, thanks to the JN.1 variant, and respiratory syncytial virus (RSV). With various similarities and differences in disease presentations, how challenging is it for physician’s to distinguish between, diagnose, and treat COVID-19 vs RSV and influenza?

While these three respiratory viruses often have similar presentations, you may often find that patients with COVID-19 experience more fever, dry cough, and labored breathing, according to Cyrus Munguti, MD, assistant professor of medicine at KU Medical Center and hospitalist at Wesley Medical Center, Wichita, Kansas.

“COVID-19 patients tend to have trouble breathing because the alveoli are affected and get inflammation and fluid accumulating in the lungs, and they end up having little to no oxygen,” said Munguti. “When we check their vital signs, patients with COVID tend to have hypoxemia [meaning saturations are less than 88% or 90% depending on the guidelines you follow].”

Patients with RSV and influenza tend to have more upper respiratory symptoms, like runny nose, sternutation— which later can progress to a cough in the upper airways, Munguti said. Unlike with COVID-19, patients with RSV and influenza — generally until they are very sick — often do not experience hypoxemia.

Inflammation in the airways can form as a result of all three viruses. Furthermore, bacteria that live in these airways could lead to a secondary bacterial infection in the upper respiratory and lower respiratory tracts — which could then cause pneumonia, Munguti said.

Another note: Changes in COVID-19 variants over the years have made it increasingly difficult to differentiate COVID-19 symptoms from those of RSV and influenza, according to Panagis Galiatsatos, MD, pulmonologist and associate professor at Johns Hopkins Medicine. “The Alpha through Delta variants really were a lot more lung tissue invading,” Galiatsatos said. “With the COVID-19 Omicron family — its capabilities are similar to what flu and RSV have done over the years. It’s more airway-invading.”

It’s critical to understand that diagnosing these diseases based on symptoms alone can be quite fickle, according to Galiatsatos. Objective tests, either at home or in a laboratory, are preferred. This is largely because disease presentation can depend on the host factor that the virus enters into, says Galiatsatos. For example, virus symptoms may look different for a patient with asthma and for someone with heart disease.

With children being among the most vulnerable for severe respiratory illness, testing and treatment are paramount and can be quite accurate in seasons where respiratory viruses thrive, according to Stan Spinner, MD, chief medical officer at Texas Children’s Pediatrics and Urgent Care. “When individuals are tested for either of these conditions when the prevalence in the community is low, we tend to see false positive results.”

Texas Children’s Pediatrics and Urgent Care’s 12 sites offer COVID-19 and influenza antigen tests that have results ready in around 10 minutes. RSV testing, on the other hand, is limited to around half of the Texas Children’s Pediatrics and none of the urgent care locations, as the test can only be administered through a nasal swab conducted by a physician. Since there is no specific treatment or therapy for RSV, the benefits of RSV testing can actually be quite low — often leading to frustrated parents regarding next steps after diagnosis.

“There are a number of respiratory viruses that may present with similar symptoms as RSV, and some of these viruses may even lead to much of the same adverse outcomes as the RSV virus,” Galiatsatos said. “Consequently, our physicians need to help parents understand this and give them guidance as to when to seek medical attention for worsening symptoms.”

There are two new RSV immunizations to treat certain demographics of patients, Spinner adds. One is an RSV vaccine for infants under 8 months old, though there is limited supply. There is also an RSV vaccine available for pregnant women (between 32 and 36 weeks gestation) that has proven to be effective in fending off RSV infections in newborns up to 6 months old.

Physicians should remain diligent in stressing to patients that vaccinations against COVID-19 and influenza play a key role in keeping their families safe during seasons of staggering respiratory infections.

“These vaccines are extremely safe, and while they may not always prevent infection, these vaccines are extremely effective in preventing more serious consequences, such as hospitalization or death.”