Twenty-five students within the Ann Arbor Public Schools have confirmed cases of whooping cough, according to a Washtenaw County Health Department official, and more are expected before the end of the school year.

AAPS spokesperson Liz Margolis said the whooping cough cases. also known as pertussis, have occurred during a month-long period. The cases have been reported at Pioneer High School, Slauson Middle School and Skyline High School.

File photo showing a young man receiving a whooping cough vaccination. Jae C. Hong | The Associated Press

"Public health is working very closely with us on that," Margolis said. "Most of the students have gone through their rounds of medication."

AnnArbor.com reported Saturday five students at Pioneer High School were diagnosed with pertussis.

Margolis said the county has told AAPS not to do anything out of the ordinary or in addition to their normal cleaning procedures.

"Most of the kids had some kind of connection where they had been near each other," Margolis said. "One of the large frustration for public health is that doctors haven’t been testing for this... They’re encouraging doctors to test for it. Our school nurses are really working and we're doing a lot of communicating to families. At this point, we're taking all of our leads from public health. We're sending information sheets home as we continue to hear cases."

Laura Bauman, epidemiologist at the Washtenaw County Public Health Department, said countywide including the AAPS cases, 32 have been confirmed. Bauman said that number is from a period between January 1 up until May 23.

In all of 2012, there were 28 cases, and in 2011 there were 26. Bauman said the county is expecting more cases before the end of the year. However, Bauman said it's too early to tell whether the numbers will reach the height of 2010 when the county had 232 confirmed cases.

"Once pertussis gets circulating, it gets going for awhile," Bauman said. "We certainly expect more cases during this school year, but we may see a dropoff during summer."

Bauman said pertussis can still spread during the summer due to a large number of children attending summer camps and other activities. Bauman said the numbers could spike again when children return to school in the fall.

Skyline principal Sulura W. Jackson sent an email out to parents Tuesday, informing them a student was diagnosed with pertussis and that can spread easily in schools.

Pertussis is a highly contagious disease that can be severe, particularly in young children, Bauman said.

Bauman said since 2009, the county has seen an uptick in cases.

"In 2009 there were 89 cases and we had no idea that the next year was going to be four times that," Bauman said. "It seems to go in waves. Part of what's going on is 10 to 15 years ago, we switched over to a new vaccine called acellular pertussis. It's a good vaccine, but it doesn't look like it's as protective as the old vaccine."

Bauman said the old vaccine caused a lot of reactions in patients who received it.

Bauman, said the new vaccine is 80 percent effective, leaving room for 20 percent of people to still get sick despite receiving it. Some of the students diagnosed had received the vaccine.

"We definitely are seeing fully-vaccinated kids," Bauman said. "That's certainly frustrating for families who have done the right thing and vaccinated their kids and for us in public health. What we saw in 2010 is that once it gets a foothold, it can affect a lot of different people."

Bauman said having a well-vaccinated population will help curb the spread, but an occasional breakthrough will occur.

Bauman said those who are diagnosed with pertussis should stay home for the five days they're on antibiotics and often, family members are prescribed medicine as well to prevent a further spread.

Pertussis can affect anyone, ranging from infants to the elderly, Bauman said.

People of all ages are advised by the health department to call their physician if they are experiencing any of the following symptoms:

Unusual cough lasting 7 days or more (with or without the signature "whooping" sound)

Sporadic bursts of coughing

Coughing-induced vomitting

The health department also is suggesting antibiotics for individuals exposed to the disease in the following categories:

All children sharing a childcare classroom with a preschool child who has pertussis

Anyone sharing a classroom or work space with someone with the disease

Infants less than 1 year old exposed to pertussis

Pregnant women exposed to the disease

People living with or working with infants and pregnant women who have been exposed to the disease

Immune-compromised people (those on chemotherapy or other drugs that affect one's immune system) who have been exposed

Anyone with a chronic respiratory disease, including asthma, who have been exposed

Anyone experiencing cold-like respiratory symptoms and that have been exposed to a person with pertussis are advised to stay home from school and work until they have completed at least five days of antibiotics.

The Washtenaw County Health Department's website has more information on pertussis and its symptoms. Bauman said the website likely will be updated once a week with new diagnosed cases.

Katrease Stafford covers Ypsilanti for AnnArbor.com.Reach her at katreasestafford@annarbor.com or 734-623-2548 and follow her on twitter.