The Chinese call it “the 100-day cough,” and hearing this, I am reminded of another reference: “The Hundred Years’ War.” Both the cough and the war were persistent, could be divided into phases and could result in tragedy.
Pertussis, also known as “whooping cough” because of the characteristic violent sound it produces, was first described in the 1600s. But it would be another 300 years before the causative bacteria, coccobacillus Bordetella pertussis, a highly contagious gram-negative organism, was discovered. U.S. epidemiologists have been tracking pertussis cases since first reports to the Public Health Service in 1922, and in the 1920s Dr. Louis Sauer perfected a vaccine.
Before pertussis vaccination became routine in the 1940s, approximately 200,000 to 250,000 cases were reported annually. Once the DPT vaccine was introduced, the numbers declined steadily until they reached an all-time low in 1976, when the CDC recorded just over 1,000 cases.
Since then, however, reports of pertussis among adults and adolescents have increased in disproportionate numbers, and pertussis remains one of the leading causes of vaccine-preventable deaths worldwide. This is likely due to the waning effects of childhood vaccinations coupled with the fact that many clinicians are not implementing the 2006 Advisory Committee on Immunization Practices’ recommendations for a one-time Tdap booster (containing the acellular pertussis vaccine) for adults and adolescents. Only 5.9% of eligible candidates received the vaccine in 2008.
In 2009, nearly 17,000 pertussis cases were reported to the CDC. In 2010, 8,383 cases (including 10 infant deaths) were reported in California — the highest incidence there in more than half a century. Ohio had its highest number of cases in 25 years. In Michigan, an increase in pertussis was first observed in the second half of 2008, and has continued to date.
Because the symptoms of pertussis resemble those of other respiratory illnesses, many more cases go undiagnosed and unreported. Clinicians must be mindful of the signs and symptoms — initially coryza and intermittent cough, followed by the disease’s paroxysmal phase: spasmodic cough, posttussive vomiting and inspiratory whoop, frequently lasting for weeks to months.
Nasal swab culture, polymerase chain reaction and serology tests can confirm the diagnosis, and the patient can be treated with antibiotics. Tests vary in sensitivity and specificity, so practitioners need to be cognizant of case definitions (which vary slightly between the CDC and WHO) and exercise appropriate clinical judgment to avoid over- or under-diagnosis.
Goals of vaccination and treatment include preventing and/or curtailing pertussis outbreaks to reduce morbidity and mortality, which is especially high among infants. Between 2000 and 2009, 178 of 194 pertussis deaths reported to the CDC occurred among infants aged <12 months.
Tdap is recommended for adults aged 19 to 64 years, especially those in contact with infants, and the FDA has just approved the first vaccine to prevent pertussis in adults aged 65 years and older. In addition, the ACIP is now advising previously unvaccinated pregnant women to get the pertussis vaccine in their second or third trimester rather than waiting until after they give birth. Most deaths occur in infants younger than age 2 months, and there is some evidence that vaccinated women may confer immunity to their newborns.