Pertussis in Emergency Medicine 

In the prevaccination era, pertussis (ie, whooping cough) was a leading cause of infant death. The number of cases reported had decreased by more than 99% from the 1930s to the 1980s. However, because of many local outbreaks, the number cases reported in the United States increased by more than 2300% between 1976 and 2005, when the recent peak of 25,616 cases were reported.^[1] The disease is still a significant cause of morbidity and mortality in infants younger than 2 years. Pertussis should be included in the differential diagnosis of protracted cough with cyanosis or vomiting, persistent rhinorrhea, and marked lymphocytosis.

Bordetella pertussis is an aerobic, nonmotile, gram-negative coccobacillus that attaches to and multiplies on the respiratory epithelium, starting in the nasopharynx and ending primarily in the bronchi and bronchioles. Transmission is only human to human by means of exposure to aerosol droplets. The disease is highly contagious. Approximately 80-90% of susceptible individuals who are exposed develop the disease. Most cases occur in the late summer and early fall.

A mucopurulosanguineous exudate forms in the respiratory tract. This exudate compromises the small airways (especially those of infants) and predisposes the affected individual to atelectasis, cough, cyanosis, and pneumonia. The lung parenchyma and bloodstream are not invaded; therefore, blood culture results are negative.

Frequency

United States

The rate of pertussis peaked in the 1930s, with 265,269 cases and 7518 deaths reported in the United States. This rate decreased to a low in 1976, when 1010 cases and 4 deaths occurred. The rate recently peaked to 25,616 cases (8.7 cases per 100,000 people per year) reported to the Centers for Disease Control and Prevention (CDC) in 2005 and 15,632 (5.2 per 100,000) reported in 2006. The CDC estimates that 5-10% of all cases of pertussis are recognized and reported. Pertussis remains the most commonly reported vaccine-preventable disease in the United States in children younger than 5 years.

In reported studies, 12-32% of adults with prolonged (1-4 wk) cough have pertussis.

International

In England, the percentage of people vaccinated over the last 4 decades decreased to less than 30%. This decline has resulted in thousands of cases reported recently, a rate that approaches the incidence in the prevaccination era. Similar epidemic outbreaks have recently occurred in Sweden, Canada, and Germany. Nearly 300,000 deaths from pertussis in Africa are thought to have occurred over the last decade.

Mortality/Morbidity

The mortality rate had been greater than 50%. Now, the mortality rate for hospitalized patients in the United States and in Europe is about 1 per 500 cases (< 0.2% of those reported). The overall infant mortality rate is 2.4 per 1 million live births. The CDC reported 39 deaths from pertussis in 2005; 32 (82%) occurred in infants younger than 3 months. The World Health Organization (WHO) estimates that 294,000 children died from pertussis worldwide in 2002.

• About 90-95% of patients die from secondary pneumonia, dehydration, hypoxia, encephalopathy, or cerebral hemorrhage. Cerebral hemorrhage occurs secondary to paroxysmal coughing, which elevates the intracranial pressure (ICP).
• Today, about 10-25% of children younger than 4 years and 2-4% of all persons with pertussis secondarily develop bacterial pneumonia. Approximately 1-2% of infants and 0.3-0.6% of adults develop seizures, which are believed to be a result of hypoxia or cerebral hemorrhage from the prolonged coughing spells. About 0.1% develop encephalopathy.
• In the prevaccination era, pertussis caused more than 270,000 cases and nearly 10,000 deaths annually. This rate reached a low of 4 reported deaths in the United States in 1982 and has recently risen to an average of about 25 deaths annually, with 39 being reported in 2005.

Sex

Pertussis is more common in girls than in boys.

Age

• Pertussis occurs predominantly in those aged 3 months to 5 years, with more than 70% of cases reported in children younger than 5 years.
• Because of the lack of maternal immunity transfer, 10-15 % of all cases occur in infants younger than 6 months, yet more than 90% of all deaths occur in this same age group. However, the growing majority of cases are now in those aged 10 years and older, which has led to increased booster recommendations.
• The natural disease does not provide lifelong immunity as earlier thought. Three injections of the cellular or acellular vaccine provide up to 12 years of protection. These vaccinations help account for the more than 10-fold increase reported in those older than 18 years.