WHOOPING COUGH
Whooping cough (pertussis) is a highly contagious respiratory infection due to Bordetella pertussis, characterized by recurrent bouts of severe paroxysmal cough and typical whoop at the end of it.
Incidence of pertussis has significantly declined in recent years due to widespread immunization.Epidemiology: B. Pertussis-a gram negative coccobacilli, is present in nasopharyngeal secretions of clinical or sub- clinical infected case and spreads via droplets. Infectivity period spans from 1 week post-exposure to 3 weeks after onset of paroxysmal stage, with maximum infectivity in catarrhal phase.
W. cough is primarily a disease of infants and preschool children lt; 5 years, including newborns due to absence of maternal antibodies. Immunity after natural infection or immunization wanes after 3-5 years, responsible for increasing number of cases being seen in previously immunized older children and adolescents. Maximum cases occur in late winter/early spring season.
Pathogenesis: It is a non-invasive infection, with localized multiplication of organisms in respiratory epithelium with marked inflammation, necrosis and secondary infection. A specific pertussis toxin and other bioactive substances, produced by B. pertussis, contribute to pathology and development of immunity.
Clinical manifestations: Incubation period is 7-14 days. W. cough is a lengthy disease (also termed 100-day cough) with three stages:
• Catarrhal stage (2 weeks) begins as a non-specific upper respiratory infection with mild fever, coryza, conjunctival congestion and cough, which is initially dry, intermittent and irritating, mainly in nights.
• Paroxysmal stage (2-4 weeks), characterized by recurrent bouts of cough with typical sequence of events - each bout begins with sudden onset of
explosive cough, often precipitated by trivial stimuli, e.g. sucking, cold-exposure, etc.
During the bout, the child is anxious, appears choked with suffused face and frequent protrusion of tongue. At the end of bout, the hallmark whoop—an inspiratory crowing sound, is produced by air rushing-in during inspiration, through partially closed glottis. Most episodes usually terminate with vomiting and production of small, thick-tenacious sputum. Child appears exhausted and sweats profusely.Frequency and severity of paroxysm increase gradually over next few weeks, till convalescence.
• Convalescent stage (2-4 weeks) is associated with decreasing frequency and severity of cough bouts, return of appetite and general well-being.
Clinical examination may reveal complications of explosive cough, e.g. conjunctival hemorrhage or tongue lacerations, but no significant lung findings.
Complications may develop due to forceful coughing, secondary infections and reduced dietary intake, as child is scared of feed-precipitated bouts (Table 10.11).
Diagnosis must be suspected in any unimmunized preschool child with prolonged cough (gt;14 days) and at least one of the following features: (a) paroxysmal nature, (b) typical whoop and/or (c) post-tussive vomiting. Absolute lymphocytosis is common and supports the diagnosis. Further confirmation is possible with:
• Rapid diagnostic tests, e.g. direct fluorescent antibody test in nasopharyngeal secretions or laryngeal swab. Serological tests, e.g. ELISA to detect major pertussis antibodies are sensitive, but not in early stages.
• Culture on Bordet-Gengou media either from nasopharyngeal swab or preferably by direct inoculation (asking the baby to cough directly on culture-plate) is the gold standard for diagnosis, though yield is maximum in catarrhal stage.
• PCR test in nasopharyngeal secretions. Cultures or PCR tests are often negative in partly-immunized cases or in late paroxysmal stage.
D/D includes other causes of whoop or paroxysmal cough, e.g. (a) other infections, e.g. B. parapertussis, mycoplasma, chlamydia, adenoviral infections, (b) airway foreign body, (c) tubercular lymph nodes, compressing trachea/bronchi, etc.
Treatment: Pertussis is self-limiting, with a limited role of antimicrobial therapy, unless instituted in very early stage. All infants lt; 6 months or older children with complications, must be hospitalized.
Management aims to limit the number of paroxysms, maintain the nutrition and general health, and treat complications, by:
• Isolation for at least 5 days after starting erythromycin therapy,
• Prevention of attacks by nursing in quiet comforting environment, avoidance of large feeds and exposure to cold draught,
• Management of acute attack: Though reassurance is usually enough to relieve anxiety, prolonged attack may need airway maintenance, oxygen or ventilatory support. Nebulized salbutamol may be effective in controlling the attack.
• Antibiotic therapy with Azithromycin (PO 10 mg/kg/ day q24hr ? 5 days) or other macrolides are effective only if given in early catarrhal stage. It shortens the natural course, reduces severity as well as infectivity and prevents secondary infection.
Other agents, e.g. steroids, salbutamol, hyperimmune pertussis immunoglobulin, etc. are of no proven value.
• Supportive treatment to ensure adequate hydration, nutrition and treatment of complications.
Prevention depends on:
• Routine immunization with whole-cell killed vaccine (DTwP) or acellular pertussis vaccine (DTaP) at 6th, 10th and 14th weeks of life with booster at 18 months and 5 years (see Ch 9.2.1)
• Isolation of the index case, specially from high-risk contacts, e.g. newborns.
• Prompt treatment of contacts: Since pertussis is highly contagious with secondary attack rate of 60-70%, all unimmunized household contacts lt;7 years of age should receive PO Azithromycin for 5 days or erythromycin for 14 days, along with immediate pertussis vaccination including those who received their 3rd primary dose before 6 months or booster dose before 3 years.
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