The number of confirmed cases of whooping cough in McHenry County has jumped to 25 and has spread to another community, the McHenry County Department of Health reports.
Last week, health officials confirmed nine students at Cary-Grove High School in Cary had the contagious bacterial infection that causes a range of symptoms similar to a common cold.
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The latest report now includes 21 students at the high school and two cases each at Crystal Lake's Lundahl Middle School and Cary's Deerpath Elementary School, a health department news release said.
The school districts did not return calls Wednesday for comment.
McHenry County Department of Health spokeswoman Debra Quackenbush, said the individuals are not related, meaning they do not live together.
Quackenbush added other cases are possible.
"We are waiting for test results for additional cases that are not in the same communities," Quackenbush said. "This has spread beyond the origin of the original outbreak."
Whooping cough -- or pertussis -- is easily spread through coughing and sneezing, health department officials said.
Students who are receiving antibiotics need to stay home for five days to complete treatment, health officials said.
"We have been hearing from schools that children are being sent back early and that will continue the spread of the virus, Quackenbush said. "We are really stressing to parents the importance of keeping children home or we will not get a handle on this."
In 2010, there were nine reported cases of whooping cough in the county, down from the 51 reported in 2009. Those figures pale in comparison to the 200 cases reported in 2004 during a northern Illinois breakout, Quackenbush said.
Next year, the state will require all high school freshmen to receive a booster shot.
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.
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.
Health authorities recommend that if you live with someone with whooping cough that you also take antibiotics to halt its spread.
For details, visit www.mcdh.info or call MCDH's Communicable Disease Division at (815) 334-4500.