Colorado has seen a spike in walking pneumonia cases this fall, especially among very young children who are typically not as susceptible to the disease, health officials said.

Bacterial infections that cause a mild lung infection have resurfaced nationwide this year for the first time since the pandemic began, peaking in August after rising sharply since the spring, according to the Centers for Disease Control and Prevention.

In Colorado, cases of walking pneumonia peaked a little later, in September, but the disease is expected to continue to spread at a high rate in the new year, Dr. Kevin Messacar, an infectious disease specialist at Children’s Hospital Colorado.

Doctors are also detecting cases more often in younger children, ages 2 to 4, although the infections have historically been more common in school-age children, he said.

“What we are seeing now is an increase several times what we normally see,” Messacar said.

The bacteria Mycoplasma pneumoniae, which causes walking pneumonia, spreads via respiratory droplets when a person sneezes or coughs. Mycoplasma pneumoniae infections don’t spread as quickly as other illnesses like the flu, and can take weeks to spread through an entire family, Messacar said.

According to the CDC, the spread of the bacteria can be prevented by washing your hands and covering your mouth and nose when coughing or sneezing.

Walking pneumonia is typically milder than other forms of pneumonia and symptoms include fever, chills, sore throat and rashes. The hallmark of the disease is “an excruciating, persistent cough” that settles in the lungs and can last up to four weeks, Messacar said.

According to the CDC, the illness is called walking pneumonia because people with this illness may not stay in bed or even at home because their symptoms are milder. However, more serious cases could result in hospitalization, Messacar said.

Health officials said they are unsure exactly how common walking pneumonia is in Colorado — including how many children have been hospitalized with the illness — because testing is not common. Recently, a three-year-old in Colorado was hospitalized with pneumonia while walking, CBS Colorado reported.

The Colorado Department of Public Health and Environment has not received any reports of walking pneumonia outbreaks this fall, but has seen an increase in patients visiting hospital emergency rooms with such infections, spokeswoman Kayla Glad said in a statement.