Pertussis is rearing its ugly head in Lancaster County again this year, with area schools reporting three cases of the highly contagious disease in as many months.

The first was in December at McCaskey High School. The others were reported in the past week at Warwick High School and Martic Elementary School.

The potentially deadly disease, also known as whooping cough, has been on the rise nationwide for the past few decades, prompting officials to urge increased awareness and prevention.

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The U.S. Centers for Disease Control and Prevention says the very young are most at risk for whooping cough, with about half of infants who contract it requiring hospitalization. Historically, there has been at least one death reported for every 100 hospitalized infants.

State records show that Lancaster County averaged about 25 cases a year for the past decade. That’s on par with the rest of the state, according to Pennsylvania Department of Health spokesman Wes Culp. This year, so far, there have been “less than five” cases.

“It is still too early to know how this year will shape up,” Culp said.

About the cases

Warwick and Martic reported that the department of health informed them of the cases on Feb. 29 and Feb. 26, respectively.

A Warwick letter to parents and guardians, sent Tuesday, says the student was diagnosed about a month ago.

A similar Martic letter sent Friday does not indicate a time frame for the student’s diagnosis, saying only that "It has come to our attention that you/your child may have been exposed to a person who has pertussis."

According to a March 1 blog post on the Martic website, the school sent the letter to the homes of the children who ride the same bus or are in the same classroom with the child.

The schools and the department said they could not divulge whether students who contracted the disease had been vaccinated or not, because of privacy laws.

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What to do

The letters from the schools direct those who have symptoms of whooping cough to contact a doctor promptly.

If a case of pertussis is diagnosed, they say, everyone in the family should be treated with antibiotics and the student should stay out of school for the first five days after beginning treatment as precautionary measures.

They also urge vaccinations as "the best way to control pertussis in the future."

On the rise

Pertussis is a highly contagious disease spread through coughs and sneezes. It begins with mild cold-like symptoms and progresses to severe coughing, and can lead to pneumonia or even death.

Nationwide, CDC statistics show the number of cases annually peaking in the 1930s at more than 250,000.

After pertussis vaccines became widely available in the 1940s, the count petered off to just a few thousand, then began rising again in the 1970s, hitting about 48,000 cases and 20 deaths in 2012.

The CDC attributes the rise to a mix of factors, including better reporting and a 1990s switch to a safer vaccine that does not appear to protect people as long as the previous one did.

The current vaccine is about 70 percent effective in the first year after people receive it, according to the agency, and 30 or 40 percent effective by the fourth year.

However, the CDC also says that children who have been fully vaccinated against pertussis are eight times less likely to get the disease than the unvaccinated, and that people who get the disease after being vaccinated are less likely to develop serious complications.

“Keeping up-to-date with recommended pertussis vaccines,” the agency says, “is the best way to protect you and your loved ones.”

This story was updated at 4:15 p.m. March 3 to include historical context from the CDC.