It's a comeback that nobody's happy about. Pertussis, also known as whooping cough, was basically eradicated in the United States until a few years ago.
"It came as a surprise to everyone in infectious diseases and public health," said William Schaffner, professor of preventive medicine at Vanderbilt University School of Medicine.
The medical community knows why the highly contagious and potentially fatal disease is spreading, but it's difficult to control the problem, Schaffner said.
Before the first effective vaccine was developed in 1940, thousands died every year from the respiratory infection. Today, whooping cough is controlled by a less-than-perfect vaccination.
"The vaccine we're using today offers good protection," but that protection wanes after about five years, Schaffner said. "Newborns are particularly susceptible. Older adolescents can still catch it but usually in a milder form," he said.
A new government study exposes another defect in the vaccine: While the vaccine protects people from getting sick, it may not prevent them from spreading the disease.
In the study, published in November in the journal Proceedings of the National Academy of Sciences, baboons were vaccinated then exposed to whooping cough. While the animals didn't get sick, the baboons did carry the bacteria in their systems for five months, meaning they could possibly be carriers of the disease while not exhibiting the coughing symptoms.
Children get their first three doses of whooping cough vaccine at 2, 4 and 6 months. According to the Centers for Disease Control and Prevention, 95 percent of kids in the U.S. get those first vaccinations. Because immunity wears off over time, the CDC recommends that adults receive one booster shot after age 18.
The issue is that so few people, only about 8 percent of adults, get the recommended booster, according to the CDC.
Also encouraging the resurgence of whooping cough is the anti-vaccine movement. Certain segments of the population decline to have their children vaccinated, Schaffner said. Some people disagree with the compulsory requirements of vaccines; others would prefer to go a more natural route.
Because of the amount of vaccines children are required to get, some parents choose to make their own vaccination schedule, ignoring what's recommended by the medical community and U.S. government.
"It's true children get more vaccines now (than in the past). They may get three or four in one visit," Schaffner said.
However, some parents ask if they can stretch out the time in between vaccinations, which can lead to missed doses.
"Some people are skeptical about vaccines" because the vaccination program has been so successful that adults today may not understand the damage these childhood diseases can do, Schaffner said. "Now, when it's time to get their own children vaccinated, they want to stretch out the (vaccination) timeline or withhold the vaccines entirely."
While whooping cough can pop up anywhere, California, Oregon and Washington state have been hardest-hit. In a 2010 outbreak in California, more than 9,000 cases were reported and 10 infants died.
That's a shocking number because it is more than nine times the recorded number of cases across the entire United States in 1976, when a concerted effort all but wiped pertussis off the map.
In 2012, more cases of whooping cough were recorded than any year since 1955, according to government figures.
What it's like
If you want to understand just how horrible whooping cough can be, "ghastly" videos of infants and children coughing so hard they cannot catch their breath are available on the Internet, Schaffner said. "They cough and cough and cough and cough. Then comes the whoop, a high-pitched gasp for air," he said.
The cough can be so prolonged it can lead to fainting, nausea and vomiting. It can disrupt sleeping and eating, and "it can actually break ribs," Schaffner said.
"It's an unusual kind of infection with a long clinical course," he said. It's aptly called the cough of 100 days.
To protect yourself and your children, be sure to follow the recommended vaccine schedule and after age 18 follow up with a booster shot, Schaffner said.
The whooping cough vaccine comes in combination with the vaccines for diphtheria and tetanus. Abbreviated as DTaP, it protects against all three.
Meanwhile, Schaffner said, scientists and researchers are hard at work developing a better vaccine.