A: Marlene, whooping cough, also known as “pertussis,” is a serious disease. It was much more common before the pertussis vaccine was developed in the 1940s. Once babies started getting the vaccine routinely, the number of cases dropped by about 99 percent.

However, health authorities are concerned that there has been an increase in pertussis cases in the United States and Canada over the past 20 years. In fact, pertussis is the only vaccine-preventable disease that has been increasing.

Pertussis is a respiratory illness caused by the bacteria bordetella pertussis. The illness usually begins with nasal congestion and a runny nose, which lasts about a week. This is followed by a cough, which can last for weeks to months. The cough can come in waves, with a series of coughs one right after another. Infants under 12 months of age, especially those under 4 months and premature babies, are more susceptible to developing pneumonia and getting seriously ill because the inflammation in their lungs and the repeated coughing makes it hard for them to breathe. After a fit of coughing, they can struggle to pull in a big breath, leading to the “whooping” sound. They can also cough so hard that they vomit, turn blue from lack of oxygen or have seizures. Babies who are ill with pertussis need urgent treatment.

Pertussis is spread the same way as the common cold—by sneezing, coughing and contact with infected mucus. The recent increase in cases is thought to come from several factors: The vaccine used in the 1980s was not as effective as the current vaccine, so adolescents’ and young adults’ immunity to pertussis has worn off over time. Also, some families chose not to have their children vaccinated with the older vaccine for fear of the rare side effect. This has left many older children and adults susceptible to catching pertussis. Currently, half of the pertussis cases are among children over 10, and 20 percent are in adults over 20. When older children and adults get pertussis, they may have a mild cough for a long time, not bother to see the doctor to get the diagnosis and treatment, and not realize that they could spread it to babies who could get seriously ill.

How can you protect your baby from getting pertussis? The best way is to make sure your baby gets immunized against it. The shots known as DTaP (a combined Diptheria, Tetanus and Acellular Pertussis vaccine) are given at 2, 4 and 6 months of age, with boosters between 15 and 18 months and 4 to 6 years. Be sure to start the vaccines on time and stay up-to-date on your baby’s shots. If you breastfeed your baby—for a year or more, if possible—it can increase your baby’s immunity against pertussis and many other illnesses. Also, try to keep your baby away from older children and adults who are coughing. If you develop prolonged coughing, be sure to cover your mouth when you cough, and call your doctor to see if treatment may be needed. In the future, keep your eye out for a pertussis vaccine for adolescents and adults.

For more information visit the Centers for Disease website, www.cdc.gov