Before widespread use of the pertussis vaccine, which became available in the 1940s, the disease killed more than 5,000 people in the United States each year. By 1976, the number of cases had decreased by more than 99%. The disease is still cyclical, however, said Ken August, a spokesman for the California Department of Public Health, leading to a spike in cases every five years or so. The last peak year was 2005.
What are the symptoms?
The symptoms vary by age.
For infants and children younger than 2, early symptoms include a runny nose and cough, which often are dismissed as being caused by a cold. As the illness progresses, the symptoms can become more severe and may include bursts of deep, rapid coughing, thick mucus, and post-cough vomiting. Complications can include pneumonia and seizures.
Those younger than 6 months don't make the characteristic "whooping" sound and thus their illness is especially likely to go undiagnosed. In the latter stage of the disease, the symptoms may increase in severity and may also include cyanosis, a blue discoloration around the fingernails and lips. By this time, the infant's condition is usually dire.
Symptoms are most pronounced in children between the ages of 2 and 10 because they're more likely to make the traditional sounds associated with whooping cough.
Adults and teenagers exhibit less noticeable symptoms, usually a cough that lasts for one or two months and feelings of suffocation or not being able to catch one's breath.
Is it possible to have the disease but not know it?
Yes, and it is especially common for adults to be undiagnosed.
Dr. John Talarico, chief of the immunization branch at the California Department of Public Health, says that 15% to 20% of adults who have had a cough for longer than a week likely have pertussis.
Because adult cases of pertussis are rarely fatal, many adults do not worry about getting vaccinated against the disease, as it is often not considered a great danger. However, because it is a contagious disease, an untreated adult can transmit the disease, posing a risk to non-afflicted people.
Who is most likely to become seriously ill from the disease?
Infants less than a year old are the most at risk, especially those younger than 3 months. They are most likely to contract the illness from family or house members. According to a study by the State Surveillance Immunization Branch, 41% of infants infected with pertussis contracted the disease from a sibling, 38% from their mother and 17% from their father.
To protect unvaccinated infants, health officials recommend that anyone who will come into contact with the newborn — parents, siblings, family, caregivers, etc. — get vaccinated. This strategy is known as "cocooning."
But as Talarico points out: No one knows when he or she might come into contact with an infant or pass it on to someone who does come in contact with an infant. For that reason, he says, everyone should be vaccinated.
"Although the danger is highest amongst infants, this does not mean that adults should not get vaccinated. Even if there is no infant in your family, if you are an adult and you have not had a booster shot, you should get one," he said.
Reducing the number of deaths caused by the disease is the most pressing issue, but reducing the number of whooping cough cases is a means to that end.