Background
Pertussis, commonly known as whooping cough, is a respiratory tract infection characterized by a paroxysmal cough. It was first identified in the 16th century. In 1906, Bordet isolated the most common causative organism, Bordetella pertussis.Bordetella parapertussis has also been associated with whooping cough in humans. Before the advent of vaccinations, pertussis was a major cause of morbidity and mortality among infants and children. Reported cases of pertussis decreased by more than 99% after the introduction of pertussis vaccine combined with diphtheria and tetanus toxoids in the 1940s. However, despite considerable advances in the control of infectious diseases in children through global immunization programs, pertussis remains a disease of public health concern.
Pathophysiology
Humans are the sole reservoir for B pertussis and B parapertussis. B pertussis is a gram-negative pleomorphic bacillus that spreads via aerosolized droplets from coughing of infected individuals. B pertussis attaches to and damages ciliated respiratory epithelium.
Epidemiology
Frequency
United States
Since the early 1980s, pertussis incidence has cyclically increased, with peaks occurring every 2-5 years.[1] Most cases occur between June and September. Neither acquisition of the disease nor vaccination provides complete or lifelong immunity. Protection against typical disease wanes 3-5 years after vaccination and is not measurable after 12 years.
From 1980-2005, the reported incidence of pertussis in the United States dramatically increased across all age groups. Although the largest increase in pertussis cases has been among adolescents and adults, the annual reported incidence remained highest among infants younger than one year, at 55.2 cases per 100,000 population.[2, 3]
International
The worldwide incidence is estimated to include 48.5 million cases and nearly 295,000 deaths per year.[4] The case-fatality rate among infants in low-income countries may be as high as 4%.
Mortality/Morbidity
Infants born prematurely and patients with underlying cardiac, pulmonary, neuromuscular, or neurologic disease are at high risk for complications of pertussis (eg, pneumonia, seizures, encephalopathy, death). Older children, adolescents, and adults often have mild or atypical illness. Approximately one half of adolescents with pertussis cough for 10 weeks or longer. Complications among adolescents and adults include syncope, sleep disturbance, incontinence, rib fractures, and pneumonia.
Compared with older children and adults, infants younger than 6 months with pertussis are more likely to have severe disease, to develop complications, and to require hospitalization. From 2001-2003, 69% of infants younger than 6 months with pertussis required hospitalization.[2]
Pneumonia, either from B pertussis infection or from secondary infection with other pathogens, is a relatively common complication, occurring in approximately 13% of infants with pertussis.[5]
CNS complications such as seizures and encephalopathy are less common and are thought to result from severe paroxysm-induced cerebral hypoxia and apnea, metabolic disturbances such as hypoglycemia, and small intracranial hemorrhages.
Reported deaths due to pertussis in young infants have substantially increased over the past 20 years.[6, 7, 8] From 1990-1999, the case fatality rate was approximately 1% in infants younger than 2 months and less than 0.5% in infants aged 2-11 months. Pertussis has been reported as a cause of sudden infant deaths.
Race
Data on race were available for 75% of patients younger than 20 years from 1997-2000.[9] Of these patients, 88% were white, 8% were black, 2% were Asian/Pacific Islander, and 2% were American Indian/Alaska Native. In comparison, the national population estimates for persons younger than 20 years in 1998 were 79% white, 16% black, 4% Asian/Pacific Islander, and 1% American Indian/Alaska Native.
Sex
From 1997-2000, among pertussis cases in patients younger than 20 years, males and females were equally affected.[9]
Age
From 2001-2003, of patients with pertussis, 23% were younger than 1 year, 12% were aged 1-4 years, 9% were aged 5-9 years, 33% were aged 10-19 years, and 23% were older than 20 years.[5]
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