Pertussis is a respiratory illness commonly known as whooping cough. It is a very contagious disease. It is spread from person to person when infected people cough or sneeze while in close contact with others. Before the availability of the pertussis vaccine, pertussis was a major childhood illness and a leading cause of death. There has been a gradual increase in pertussis rates over the last 20 years. The most cases occur in unimmunized infants younger than 1 year of age. In 2012, 48,277 cases of pertussis (whooping cough) were reported in the U.S., but many more go undiagnosed and unreported. This is the most number of cases reported in the U.S. since 1955. Symptoms usually begin within five to 10 days of being exposed, but may be delayed for up to three weeks. The disease usually starts with cold-like symptoms and maybe a mild cough or fever. It may initially be indistinguishable from a minor upper respiratory tract infection. After one to two weeks, severe coughing can begin. Unlike the common cold, pertussis can become a series of coughing fits that continues for weeks. In infants, the cough can be minimal or not even present. Infants may have a symptom known as apnea, which is a pause in the child\u2019s breathing pattern. Pertussis is most dangerous for babies. About half of infants younger than 1 year of age who get the disease are hospitalized, and one or two in 100 hospitalized infants die. Pertussis can cause violent and rapid coughing, over and over, until the air is gone from the lungs and you are forced to inhale with a loud \u201cwhooping\u201d sound. This extreme coughing can cause you to throw up and be very tired. The \u201cwhoop\u201d is often not there and the infection is generally milder in teens and adults, especially those who have been vaccinated. Because pertussis in its early stages appears to be nothing more than the common cold, it is often not considered until the more severe symptoms appear. Persons with pertussis are contagious from the onset of runny nose, sneezing, low-grade fever (symptoms of the common cold) through the third week after the onset of multiple, rapid coughs or until 5 days after the start of effective antimicrobial treatment. Pertussis can be diagnosed by taking into consideration if you have been exposed to pertussis and by doing a history and physical examination and laboratory tests including taking a sample of secretions from the back of the throat through the nose and by blood tests. Antibiotics work best when administered early in the disease. Treatment can also help prevent spreading the infection to other people. Even though the cough may persist for many weeks, treatment beginning after three weeks of illness is unlikely to help because the bacteria are gone from the body even though the symptoms persist. Although vaccination is not 100% effective, it remains the best way to prevent infection. Staying up to date on the pertussis vaccine is especially important for families and caregivers of infants and babies since this population is particularly vulnerable to serious disease. Pregnant women should receive the Tdap vaccine during each pregnancy, preferably at 27 through 36 weeks. Everyone around the infant should also be vaccinated, including parents, siblings, grandparents, other family members, babysitters, etc. Worldwide, there are an estimated 16 million cases of pertussis and about 195,000 deaths per year. Vaccinated children and adults can become infected with and transmit pertussis; however, disease is less likely to be severe. Contact your doctor if you have further questions about pertussis. David J. Herman, MD, FACP, is partner in the Hillsborough-based ID Care, the largest enterprise in New Jersey dedicated to the identification, treatment and prevention of infectious diseases.