That’s more than a 340% increase over the 3,962 cases reported last October.

Pre-pandemic, cases would typically exceed 10,000 per year, spiking to 18,600 in 2019.

Post-pandemic, whooping cough diagnoses plummeted, with just 2,100 cases reported in 2021.

The 10 states with the highest number of cumulative (year to date) cases include Pennsylvania (2,209), New York (1,228), Illinois (1,153), California (1,123), Wisconsin (903), Washington (844), Ohio (814), Texas (676), Oregon (546), Arizona (491).

One theory for the spike is that cases fell sharply during the COVID-19 pandemic, as mask-wearing, social distancing and other infection protocols helped to protect against whooping cough.

“They are increasing more now as our immune systems are exposed to viruses and bacteria we haven’t seen and are slower to respond,” Dr. Marc Siegel, senior medical analyst for Fox News and clinical professor of medicine at NYU Langone Medical Center, previously told Fox News Digital.

Whooping cough outbreaks typically occur when there are populations with low vaccination rates, Katy Dubinsky, a New York pharmacist and the CEO and co-founder of Vitalize, a private supplement company, previously told Fox News Digital.

“Pertussis is highly contagious, and in areas where herd immunity is not strong due to insufficient vaccination, the disease can spread more easily,” she told Fox News Digital.

“Additionally, the immunity from the vaccine or previous infection wanes over time, which can also contribute to outbreaks.”

A highly contagious respiratory tract infection, pertussis gets its more common name, “whooping cough,” from the severe hacking cough that some people develop.

In addition to the cough, initial symptoms mimic those of a cold — including nasal congestion, runny nose, fever, and red, watery eyes, according to Mayo Clinic.

Symptoms get worse over time, often leading to severe and uncontrollable coughing fits, which end with a “whooping” sound after the patient breathes in due to a buildup of mucus in the airways, the same source noted.

“This is an underappreciated problem, and a good reason why I am giving out Tdap vaccines to my adult patients regularly,” Siegel told Fox News Digital on Friday.

Symptoms get worse over time, often leading to severe and uncontrollable coughing fits, which end with a “whooping” sound after the patient breathes in due to a buildup of mucus in the airways, the same source noted.

Tdap is a combination of three vaccines that protect against tetanus, diphtheria and pertussis infections in teens and adults.

“The vaccine works — and it lasts three to five years,” Siegel said. “Everyone should have an up-to-date vaccine.”

While the vaccine offers protection against severe illness for children, infants who are too young for vaccination are at the highest risk.

“This disease is especially problematic in young children, because they have less developed airways,” Siegel cautioned.

It is recommended that pregnant women get the Tdap vaccine during each pregnancy, as it helps protect the newborn until they can receive their own vaccinations.

Due to the potential severity in young infants and those with weakened immune systems, it’s important to seek medical attention if pertussis is suspected, experts advise.

“Unfortunately, the diagnosis is often missed because the dry cough may be mistaken for a virus,” Siegel said.