Lymphocytosis is present in 75% to 85% of infants and young children but is not diagnostic. The white blood cell count may increase from 20,000 cells/mm3 to more than 50,000 cells/mm3, consisting primarily of mature lymphocytes. Physical examination and radiographic signs of segmental lung atelectasis may develop during pertussis, especially during the paroxysmal stage. Perihilar infiltrates are common and are similar to those seen in viral pneumonia.
For a young child with classic pertussis, the diagnosis based on the pattern of illness is quite accurate. The paroxysmal stage is the most distinctive part of the syndrome. Other causes of per-tussis-like prolonged cough illnesses include Bordetella parapertussis, which causes a similar but milder illness and is not prevented by B. pertussis vaccination, Mycoplasma pneumoniae, Chlamydia pneumoniae and Chlamydophila pneumoniae, adenoviruses, and respiratory syncytial virus.
Azithromycin, clarithromycin, or erythromycin are recommended for children under 1 month of age. Azithromycin should be used in neonates due to the association between erythromycin treatment and the development of pyloric stenosis. Treatment during the catarrhal phase eradicates nasopharyngeal carriage of organisms within 3 to 4 days and may lessen symptom severity. Treatment in the paroxysmal stage does not alter the course of illness but decreases the potential for spread to others. Trimethoprim-sulfamethoxazole is an alternative therapy among children older than 2 months, though studies of its use for this indication are limited.
Major complications are most common among infants andyoung children and include hypoxia, apnea, pneumonia, seizures, encephalopathy, malnutrition, and death. The mostfrequent complication is pneumonia caused by B. pertussis itself or resulting from secondary bacterial infection with Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Atelectasis may develop secondaryto mucous plugs. The force of the paroxysm may producepneumomediastinum, pneumothorax, or interstitial or subcutaneous emphysema; epistaxis; hernias; and retinal andsubconjunctival hemorrhages. Otitis media and sinusitis may occur.
Most children recover normal pulmonary function with complete healing of the respiratory epithelium. Most permanent disability is a result of encephalopathy.
Active immunity is induced with acellular pertussis components given as a vaccine in combination with the tetanus and diphtheria toxoids (DTaP). The acellular pertussis vaccines contain two to five antigens of B. pertussis, including pertussis toxin, pertactin, filamentous hemagglutinin, and fimbrial agglutinogens, FIM-2 and FIM-3. DTaP vaccine is recommended at 2, 4, 6, and 15 to 18 months, with a booster at 4 to 6 years, and has an efficacy of 70% to 90%. A single booster dose of Tdap vaccine is recommended at 11 to 12 years or once for all adults.
Macrolides are effective in preventing secondary cases in contacts exposed to pertussis. Underimmunized close contacts under 7 years of age should receive a booster dose of DTaP (unless a booster dose has been given within the preceding 3 years), whereas those 7 to 10 years of age should receive Tdap. All close contacts should receive prophylactic antibiotics for 5 days (azithromycin) or 7 to 14 days (clarithromycin or erythromycin, duration based on age).