Pertussis, also known as whooping cough, is an acute infectious disease caused by the bacterium Bordetella pertussis. Pertussis is a human disease and no animal or insect source, or vector is known to exist.
B. pertussis is a fastidious, gram-negative bacterium requiring special media for isolation. B. pertussis produces multiple antigenic and biologically active products including:
- Pertussis toxin
- Filamentous hemagglutinin (FHA)
- Adenylate cyclase
- Tracheal cytotoxin
These products are responsible for the clinical features of pertussis. An immune response to one or more of them produces immunity following infection.
Some observational studies suggest that pertussis infection can provide immunity for 4 to 20 years, but that it is not lifelong.
Pertussis is primarily a toxin-mediated disease. The bacteria
- Attach to the cilia of the respiratory epithelial cells
- Produce toxins that paralyze the cilia
- Cause inflammation of the respiratory tract, which interferes with the clearing of pulmonary secretions
Until recently, scientists thought that B. pertussis did not invade the tissues. However, recent studies suggest that the bacteria are present in alveolar macrophages.
Prevalence before and after widespread vaccination
In the 20th century, pertussis was one of the most common childhood diseases and a major cause of U.S. childhood mortality. Before the availability of pertussis vaccine in the 1940s, public health experts reported more than 200,000 cases of pertussis annually. Since widespread use of the vaccine began, incidence has decreased more than 75% compared with the pre-vaccine era.
Increase in reported cases
Since the late 1980s through the start of the COVID-19 pandemic in 2020, there was an increase in the number of reported cases of pertussis. In 2012, the last peak year, CDC reported 48,277 cases of pertussis. CDC believes that much of the disease goes unrecognized and unreported.
Several factors have likely contributed to the increase in reported cases, including
- Increased awareness and improved recognition of pertussis among clinicians
- Greater access to and use of laboratory diagnostics, especially polymerase chain reaction (PCR) testing
- Increased surveillance and reporting of pertussis to public health departments
- Waning immunity from vaccination
Additionally, B. pertussis are also always changing at a genetic level. CDC continues to evaluate what impact, if any, molecular changes in B. pertussis are having on public health.