LINCOLNSHIRE, Ill. (CBS) — A whooping cough outbreak has now infected nearly three dozen students at Stevenson High School in Lincolnshire in recent months.

A total of 35 students at Stevenson have now been diagnosed with whooping cough, or pertussis, since September. That is a school record.

CBS 2 checked with Illinois state health officials, who said cases of whooping cough are skyrocketing this year.

Already this year, there have been 517 cases nationwide, compared with just 318 for all of last year.

As to possible reasons for the rise, Stevenson officials said parents aren’t aware of the symptoms and doctors have misdiagnosed the illness.

School nurses are working with local doctors’ offices to raise awareness.

Pertussis is a contagious bacterial infection that causes a range of symptoms. It is easily spread through coughing and sneezing.

Symptoms may appear 5 to 10 days after exposure but can take three weeks to show up. Initial symptoms are similar to those of a common cold but after a week or two can develop into bursts of numerous, rapid coughs with a distinctive “whooping” sound.

The coughs can even induce vomiting.

While it can be mild in some cases, it poses a greater risk to infants who are not fully immunized, those with compromised immune systems and older people.