Pertussis occurs world-wide. Humans are both the natural hosts and reservoirs of infection. The disease is caused by Bordetella pertussis which is a Gram-negative coccobacillus. B. parapertussis and B. bronchiseptica produce milder infections. Pertussis is highly contagious and is spread by droplet infection. In its early stages it is indistinguishable from other types of upper respiratory tract infection. Epidemic disease occurred in the UK when the safety of the whooping cough vaccine was questioned. Currently, uptake exceeds 95% and the disease is uncommon.
Clinical features
The incubation period is 7-10 days. It is a disease of childhood, with 90% of cases occurring below 5 years of age. However, no age is exempt.
During the catarrhal stage the patient is highly infectious, and cultures from respiratory secretions are positive in over 90% of patients. Malaise, anorexia, mucoid rhinorrhoea and conjunctivitis are present. The paroxysmal stage, so called because of the characteristic paroxysms of coughing, begins about a week later. Paroxysms with the classic inspiratory whoop are seen only in younger individuals in whom the lumen of the respiratory tract is compromised by mucus secretion and mucosal oedema. The whoop results from air being forcefully drawn through the narrowed tract. These paroxysms usually terminate in vomiting. Conjunctival suffusion and petechiae and ulceration of the frenulum of the tongue are usual. Lymphocytosis due to the elaboration of a lymphocyte-promoting factor by B. pertussis is characteristic; lymphocytes may account for over 90% of the total white blood cell count. This stage lasts approximately 2 weeks and may be associated with several complications, including pneumonia, atelectasis, rectal prolapse and inguinal hernia. Cerebral anoxia may occur, especially in younger children, resulting in convulsions. Bronchiectasis is a rare sequel.
Diagnosis
The diagnosis is suggested clinically by the characteristic whoop and a history of contact with an infected individual. It is confirmed by isolation of the organism. Cultures of swabs of nasopharyngeal secretions result in a higher positive yield than cultures of 'cough plates'.
Treatment
If the disease is recognized in the catarrhal stage, erythromycin will abort or decrease the severity of the infection. In the paroxysmal stage, antibiotics have little role to play in altering the course of the illness.
Prevention and control
Affected individuals should be isolated to prevent contact with others, e.g. in hostels and boarding schools. Pertussis is an easily preventable disease and effective active immunization is available. Convulsions and encephalopathy have been reported as rare complications of vaccination but they are probably less frequent than after whooping cough itself. Any exposed susceptible infant should receive prophylactic erythromycin.
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