BOISE, Idaho (AP) — Health officials say a whooping cough outbreak has now sickened roughly 122 people in southwestern Idaho, and they're warning those numbers could increase with the start of the school year.

Cases of pertussis have been found throughout the Southwest District Health region, which includes Adams, Canyon, Gem, Owyhee, Payette and Washington counties.

But the bulk of them have occurred in Canyon County, where 94 people have contracted the disease. Some of those patients have been hospitalized, but health officials didn't immediately have that number available.

"July was the largest number of cases we've had so far this year with 33 cases," said Jami Delmore, environmental health supervisor of Southwest District Health. "We're concerned with the school season starting up that the numbers will go up."

The district includes Adams, Canyon, Gem, Owyhee, Payette and Washington counties, but the bulk of the cases have occurred in Canyon County where 94 people have contracted the disease.

Numbers from the Idaho Department of Health and Welfare show counties in central and southern Idaho have also been hit, with nearly 260 cases reported statewide so far in 2018. That compares to just 32 reported for all of 2017.

Whooping cough often starts with what feels like a mild cold, followed by weeks of intense coughing fits. The disease gets its name from the sound some people make at the end of a coughing jag when they gasp for breath.

Health officials warn that not everyone makes the gasping sound, and people who have been coughing for two weeks or longer should see a health care provider to check for pertussis.

"In reality it usually is just a very persistent cough that can be a lot worse at night," she said. "So we're really trying to get people, if they have a cough that is just not stopping, we want them to go in and get treated for it and keep it from spreading."

The disease is highly contagious, easily spreading to others standing as far as six feet away when a person with pertussis coughs or sneezes. But it's treatable with a five-day course of antibiotics.

Cheryl Craig, an epidemiologist with the district, says that without treatment, the contagious period lasts for weeks, starting about a week before the cough begins and lasting two to three weeks after the illness ends.

Craig said children who are diagnosed with pertussis need to be out of school or daycare for the five days that they take antibiotics, but after that they are no longer contagious.

Officials with the federal Centers for Disease Control say that before pertussis vaccines became widely available in the 1940s, about 200,000 children got sick with it each year and about 9,000 of those kids died from the infection. Today, the CDC says there are usually between 10,000 and 40,000 cases reported each year, and about 20 deaths from pertussis.