Reported cases of whooping cough continue to grow as Exeter and York, Maine, have experienced outbreaks of the respiratory disease in their schools.

At Exeter High School, the number of confirmed cases jumped from 22 on Monday to 35 by week's end. In York, there has been six confirmed cases, which according to the Maine Center for Disease constitutes a outbreak because there were three or more confirmed cases in 21 days.

Jake Leon, director of communications for the N.H. Department of Health and Human Services, said the Exeter whooping cough cases reached �outbreak� status when the confirmed cases rose from one on June 1 to the 22 on Monday.

�This is considered an outbreak because there are more cases than what would normally be observed,� Leon said. �New Hampshire typically sees 50 to 150 pertussis cases per year. The pertussis vaccine is not perfect, and people who have been vaccinated can still develop a pertussis infection, but high vaccination rates help limit disease and the spread of infection."

Pertussis is a bacterial infection of the respiratory tract that can cause a persistent cough, according to DHHS. Early symptoms usually include upper respiratory cold-like symptoms including low-grade fever, cough and runny nose. These symptoms can last for one to two weeks before progressing to the more typical syndrome that includes intense fits of coughing sometimes with a high-pitched �whoop� and occasionally ending with vomiting, according to DHHS.

The outbreak raised concern among parents of students who may have been potentially exposed in the final weeks of school. According to Dr. Apara Dave, an infectious disease specialist with Core Physicians in Exeter, whooping cough outbreaks are not all that uncommon.

�The Exeter area is pretty well-vaccinated,� Dave said. �Pertussis outbreaks here would not be driven by under-immunization. That can be the case for larger populations where people of mixed backgrounds come into close contact. That�s why it often spreads in a place like a school because there are a relatively large group of people together in one building.�

Dr. David Itkin is the infectious disease doctor for Portsmouth Regional Hospital. He said following the creation of a pertussis vaccine, the United States saw the rate of whooping cough decrease sharply to less than 5,000 cases a year before a sudden drop in immunization rates starting in the 1980s. According to the Centers for Disease Control and Prevention, there were nearly 18,000 cases of whooping cough in the United States in 2016.

�In general, New Hampshire is a highly immunized state, but there has been a steady increase in unvaccinated Americans going back to the 1980s� Itkin said. �Pertussis is a serious problem around the world. It�s highly contagious and potentially deadly for vulnerable populations like infants. That�s why parents of young children working in schools need to be very careful.�

After a person is exposed to pertussis, symptoms usually develop within five to 10 days, but in some cases may not develop for up to 21 days, according to DHHS, which added pertussis is most likely to be passed to other people during the first few weeks a person is ill. Individuals with pertussis are no longer considered contagious after a five-day course of antibiotics to treat the infection, according to DHHS.

Dave said whooping cough is transferred from person to person more from physical contact with someone who has the disease and less from the bacteria living on surfaces.

�As long as the school is being thoroughly cleaned with germicidal substances, it will drastically reduce the chance of contracting pertussis and it doesn�t require any kind of quarantine,� she said. �However, students who may be sick need to stay home until the tests are negative and take the five-day course of antibiotics.�

The vaccine for whooping cough is typically administered in four or five doses before a child turns 5. New Hampshire children entering the seventh grade in public school are required by law to get at least one round of the pertussis vaccines, diphtheria and tetanus (Tdap vaccine) on or after their seventh birthday.

According to the CDC, roughly eight or nine of every 10 children who receive five doses of Tdap will be generally protected. However, the CDC says the vaccine wanes in its effectiveness over time, protecting seven of 10 children five years after their last dose and three to four of 10 children after 10 years.

�The immunity definitely wanes and that�s a problem across the board with all vaccines,� Dave said. �However, those who have received their recommended dosages for their vaccines and get pertussis, it will be a much shorter, much less serious case of the disease. It�s similar to those who get the flu shot every year, they can still get the flu but they won�t get as sick as someone who didn�t get the shot.�

However, Itkin said doctors now recommend adults receive one additional Tdap booster once in their lives in lieu of one of their 10-year tetanus boosters. The same applies for children age 11 to 18. He also said when women become pregnant, it is advised they receive a Tdap booster to better assure they won�t pass pertussis to their infant.

Itkin believes whooping cough could have spread at Exeter High because even in the event every EHS student had received all five doses of the Tdap vaccines, it still may not have been enough.

�Was (an extra booster) the missing link that could�ve prevented the outbreak?� Itkin said. �I think if there was a fully immunized group of students with the extra booster, we would not be seeing this epidemic at Exeter.�

Despite fear among some populations that vaccines can lead to developmental disorders in children, Dave said countless studies have been conducted and no link has been discovered between vaccinations and autism. The Canadian Medical Association Journal reported in March 2010 the original scientific paper from The Lacent, which claimed the MMR (measles, mumps and rubella) vaccine caused autism, was retracted earlier that year.

�It�s been pretty much disproven scientifically,� Dave said.

Itkin said if anyone believes they may have come into contact with someone who has pertussis, it is critical for them to get checked out by their physician.