Just as mumps has resurged due to waning immunity, whooping cough, caused by the gram-negative bacterium Bordetella pertussis, also has reemerged as an important infectious disease. B. pertussis exclusively infects humans, is transmitted via airborne droplets, and is difficult to grow in culture.
The first recorded outbreak occurred in 1578, starting in Paris and spreading throughout Europe. In the early to mid-20th century, it was the leading cause of death from infectious disease in children. After vaccines were introduced in the 1940s, the incidence of disease was dramatically reduced to less than one case per 100,000 population. (Clin Infect Dis 1999; 28:1230.)
Since the 1980s, the largest increase in incidence has been in adolescents and adults. In 2003, 63 percent of reported cases were in patients older than 10. (MMWR 2005; 54:389.) In the prevaccine era, more than 93 percent of cases were in children younger than 10. (Pediatr Infect Dis J 2005;24[6 suppl]:S104.) Immunity from the vaccine is not complete in the first year of life, and as a result, more than half of childhood cases are in infants under 1 year. (MMWR 2005;54:389.)
Classically, the clinical course is described in three stages: catarrhal, paroxysmal, and convalescent, but many factors can cause an atypical presentation. The initial stage, catarrhal, consists of nonspecific, URI-like signs and symptoms: low-grade fever (high fever is uncommon), conjunctivitis, and rhinorrhea.
After seven to 14 days, the paroxysmal stage begins, characterized by coughing and debris pooling in the lungs due to disruption in ciliary function secretions. The cough is described as violent bursts, with an inspiratory “whoop.” These coughing spells can result in cyanosis, posttussive emesis, rib fractures, apnea, subconjunctival hemorrhages, seizures, and hypoxic encephalopathy. The final stage, the convalescent, begins as the cough subsides, and may last up to three months.
Atypical presentations are more common in previously vaccinated adolescents and adults and infants, manifesting in shorter duration of symptoms, lack of paroxysms of coughing, in infants feeding poorly, apnea, or bradycardia. Death from pertussis is most commonly a result of a secondary pneumonia (90% of all deaths). (Disease-a-Month 2007;53:488.) The patient is most contagious during the catarrhal and early paroxysmal stages.
The diagnosis can be made clinically, but diagnostic testing should be employed for confirmation and surveillance. A polyester swab left for 10 seconds in the nasopharynx is the best way to obtain a sample. The Centers for Disease Control and Prevention recommends a PCR with follow-up culture to test patients with suspected pertussis. (MMWR 2006;55:321.) Direct fluorescent antibody testing, culture alone, or blood serology are not recommended as diagnostic tools. This is a reportable disease, and state health departments should be contacted for confirmed or highly suspicious cases, even before the confirmatory studies have returned. Labs and chest x-rays have little value in diagnosing pertussis.
Concerning treatment, it is important to know that once the paroxysmal stage has begun, antibiotics have not been shown to reduce disease duration, but earlier antibiotic administration reduces the severity and duration of symptoms and shortens the period of communicability. (MMWR 2008;57:583.) The CDC recommends macrolides: erythromycin, azithromycin, or clarithromycin. TMP-SMX is an alternate agent, but is contraindicated in infants under 2 months. Azithromycin is the overall recommended agent, especially in infants under 1 month; a five-day course is all that is required. Postexposure prophylaxis is important for close contacts, partially immunized adults, and children of pertussis patients because it reduces communicability. The drugs and treatment length is identical to the usual treatment of the disease.
Although the effectiveness of the original pertussis vaccine was 85 percent, its protection begins to decline after four to 12 years. This, along with no passive immunity conferred to infants, has left much of the population susceptible to infection. Recently, two acellular vaccines were approved for use by the FDA. Tdap, with trade names Boostrix and Adacel, came to the market in 2005. Adacel is approved for patients 11 to 64 years old, and Boostrix is approved for use in 10- to 18-year-old patients.
Both are approved for single-dose use to add protection against pertussis and to replace the next dose of tetanus and diphtheria toxoids. The CDC's recommendation on their use in pregnant women is not clear; insufficient data exist to determine its safety in pregnancy. (MMWR 2008;57:583.) It is also unclear if these new vaccines will confer immunity longer than the older vaccine.