Pertussis

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, who also developed the first serology and vaccine. The complete B. pertussis genome of 4,086,186 base pairs was sequenced in 2002. After a 7 to 10 day incubation period, pertussis in infants and young children is characterized initially by mild respiratory infection 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 due to the sheer violence of the fit. In severe cases, the vomiting induced by coughing fits can lead 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 during the (convalescent stage). Other complications of the disease include pneumonia, encephalitis, pulmonary hypertension, and secondary bacterial superinfection.

Because neither vaccination nor infection confers long-term immunity, infection of adolescents and adults is also common  Most adults and adolescents who become infected with Bordetella pertussis have been vaccinated or infected years previously. When there is residual immunity from previous infection or immunization, symptoms may be milder, such as a prolonged cough without the other classic symptoms of pertussis. Nevertheless, infected adults and adolescents can transmit the bacteria to susceptible individuals. Adults and adolescent family members are the major source of transmission of the bacteria to unimmunized or partially immunized infants, who are at greatest risk of severe complications from pertussis. Pertussis is spread by contact with airborne discharges from the mucous membranes of infected people, who are most contagious during the catarrhal stage. Because the symptoms during the catarrhal stage are nonspecific, pertussis is usually not diagnosed until the appearance of the characteristic cough of the paroxysmal stage. Methods used in laboratory diagnosis include culturing of nasopharyngeal swabs on Bordet-Gengou medium, polymerase chain reaction (PCR), immunofluorescence (DFA), and serological methods. The bacteria can be recovered from the patient only during the first three weeks of illness, rendering culturing, PCR, and DFA useless after this period. For most adults and adolescents, who often do not seek medical care until several weeks into their illness, serology is often used to determine whether antibody against pertussis toxin or another component of B. pertussis is present at high levels in the blood of the patient. Treatment with an effective antibiotic shortens the infectious period but does not generally alter the outcome of the disease; however, when treatment is initiated during the catarrhal stage, symptoms may be less severe. Three macrolides, erythromycin, azithromycin and clarithromycin are used in the U.S. for treatment of pertussis; trimethoprim-sulfamethoxazole is generally used when a macrolide is ineffective or is contraindicated. Close contacts who receive appropriate antibiotics (chemoprophylaxis) during the 7–21 day incubation period may be protected from developing symptomatic disease. Close contacts are defined as anyone coming into contact with the respiratory secretions of an infected person in the 21 days before or after the infected person's cough began.