Pertusis Disease

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.
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
Clinical
History

Typically, the incubation period of pertussis ranges from 3-12 days. Pertussis is a 6-week disease divided into catarrhal, paroxysmal, and convalescent stages, each lasting from 1-2 weeks. The 3 stages of disease progression are as follows:

* Stage 1: The initial (catarrhal) phase is indistinguishable from common upper respiratory infections with nasal congestion, rhinorrhea, and sneezing, variably accompanied by low-grade fever, tearing, and conjunctival suffusion. Pertussis is most infectious when patients are in the catarrhal phase, but pertussis may remain communicable for 3 or more weeks after the onset of cough.
* Stage 2: Patients in the second (paroxysmal) phase present with paroxysms of intense coughing lasting up to several minutes. In older infants and toddlers, the paroxysms of coughing occasionally are followed by a loud whoop as inspired air goes through a still partially closed airway. Infants younger than 6 months do not have the characteristic whoop but may have apneic episodes and are at risk for exhaustion. Posttussive vomiting and turning red with coughing are common in affected children.
* Stage 3: Patients in the third (convalescent) stage have a chronic cough, which may last for weeks.

Older children, adolescents, and adults may not exhibit distinct stages. Symptoms in these patients include uninterrupted coughing, feelings of suffocation or strangulation, and headaches.
Physical

In patients with uncomplicated pertussis, physical examination findings contribute little to the diagnosis. In all patients with pertussis, fever is typically absent. Most patients do not have signs of lower respiratory tract disease. Conjunctival hemorrhages and facial petechiae are common and result from intense coughing.
Causes

B pertussis and B parapertussis are the causative organisms for pertussis infection in humans. Bacteria spread via aerosolized droplets from coughing of infected individuals. Humans are the sole reservoir for the organisms.

Transmission can occur through direct face-to-face contact, sharing a confined space, or through contact with oral, nasal, or respiratory secretions from an infected source. Pertussis is highly contagious, with as many as 80% of susceptible household contacts becoming infected after exposure. Family members or relatives were the suspected source of infection in 75% of cases.10

Young infants, especially those born prematurely, and patients with underlying cardiac, pulmonary, neuromuscular, or neurologic disease are at high risk for contracting the disease and for complications.


source : http://emedicine.medscape.com/article/967268-overview