A winter respiratory virus is spreading fast across the South, mainly infecting infants and toddlers

• The CDC says to test for RSV if a patient with a respiratory illness tests negative for COVID-19.
• There's been an uptick in RSV cases across the Southern states.
• Toddlers and older infants are susceptible. Symptoms include sneezing and wheezing.

Cases of a respiratory virus are rising across the Southern US, and it's not COVID-19.

RSV (respiratory syncytial virus) typically circulates in the fall and winter months, mainly affecting children.

But rates plummeted in 2020 - likely because of COVID-19 mitigation strategies, such as social distancing, according to an advisory warning from the Centers for Disease Control and Prevention on June 10.

As the US opens up, rates of RSV are rising, and the CDC is recommending that clinicians should test for RSV if a patient with cold or flu-like symptoms tests negative for COVID-19.

"The reason why it's spreading now is unclear, but likely relates to the reason we didn't see much RSV and influenza in the winter: masking, distancing and good handwashing," Dr. Elizabeth Murray, a pediatrician specializing in pediatric emergency medicine, told People. "As those precautions start to go away, we can expect germs to return."

Toddlers may have a higher risk of severe RSV because they weren't exposed to viruses during the pandemic

RSV spreads through coughing and sneezing, according to the CDC, and infants, young children, and older adults with chronic illnesses who get RSV are at risk for developing a severe disease. Each year, around 100 to 500 kids under the age of five die of RSV, and 14,000 deaths occur in adults older the 65.

The advisory cautioned that older infants and toddlers may be at risk of more severe RSV-associated illness because they were not exposed to the virus, as most babies are, during the winter months, and therefore did not build immunity.

For toddlers and infants six months and older, symptoms include sneezing and wheezing. "It often starts with a runny nose and maybe a fever, then often gets worse around day 3 to 5 of illness," Murray said.

While infants typically exhibit symptoms like irritability, poor feeding, lethargy.