Whooping cough

Pertussis, also known as whooping cough, is a highly contagious disease that is one of the leading causes of vaccine-preventable deaths. There are 30–50 million cases per year, and about 300,000 deaths per year (World Health Organization data). Most deaths occur in children under one year of age. Ninety percent of all cases occur in developing countries. It is caused by certain species of the bacterium Bordetella&mdash;usually B. pertussis, but some cases are caused by B. parapertussis.

Pertussis was recognizably described as early as 1578 by Guillaume de Baillou (1538-1616), but earlier reports date back at least to the 12th century. B. pertussis was isolated in pure culture in 1906 by Jules Bordet and Octave Gengou. The complete B. pertussis genome of 4,086,186 base pairs was sequenced in 2002.

Characterization
Pertussis is characterized initially by mild respiratory infections symptoms such as cough, sneezing, and runny nose (catarrhal stage). After one to two weeks the cough changes character, with paroxysms of coughing followed by an inspiratory "whooping" sound (paroxysmal stage). Coughing fits may be followed by vomiting not necessarily due to nausea but due to the sheer violence of the fit itself, which in severe cases leads to malnutrition. The fits that do occur on their own can also be triggered by yawning, stretching, laughing, or yelling. Coughing fits gradually diminish over one to two months. Other complications of the disease include pneumonia, encephalitis, pulmonary hypertension, and secondary bacterial superinfection.

Transmission
Pertussis is spread by contact with airborne discharges from the mucous membranes of infected people. Methods used in laboratory diagnosis include: calcium alginate throat swab, culture on Bordet-Gengou medium, immunofluorescence and serological methods.

Treatment of pertussis with antibiotics (often erythromycin, azithromycin, clarithromycin or trimethoprim-sulfamethoxazole) results in the person becoming less infectious but probably does not significantly alter the outcome of the disease. Close contacts who receive appropriate antibiotics (chemoprophylaxis) during the 7–21 day incubation period may be protected from developing symptomatic disease.

Vaccines
Pertussis vaccines were initially formulated in 1926&mdash;most notably by Dr. Louis W. Sauer of Northwestern University and Evanston Hospital&mdash;as whole-cell preparations, but are now available as acellular preparations, which cause fewer side effects. They offer protection for only a few years, and are given so that immunity lasts through childhood, the time of greatest exposure and greatest risk. The immunizations are often given in combination with tetanus and diphtheria immunizations, at ages 2, 4, and 6 months, and later at 15–18 months and 4–6 years.

Traditionally, pertussis vaccines are not given after age seven, as the frequency of side effects associated with the immunization tends to increase with age. The most serious side-effects of immunization are neurological: they include seizures and hypotonic episodes. An acellular vaccine preparation for older individuals is available in Canada and Europe, and two such products are being evaluated for their safety in adolescents and adults in the United States; a Food and Drug Administration decision was approved for use of the Adacel vaccine for 11-64 year olds in August 2005. However, it is not recommended for those who had an adverse reaction to the older vaccines.