Bordetella pertussis index
Index of pathogens
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Petit P, Brandenburg A
The micro-organism and its clinical presentation
Bordetella pertussis is an encapsulated, non-motile, small, gram negative coccobacillus that grows aerobically with special growth requirements. Humans are its only host. Bordetella pertussis is transmitted by droplets and colonises the nasopharynx adhering specifically to ciliated cells. Subsequently the respiratory mucosa is primarily damaged by excretion of multiple exotoxins. An important virulence factor is pertussis toxin (PT) which is unique for Bordetella pertussis and is not produced by other Bordetella spp. PT probably disrupts host immune responses and is an essential factor in the induction of leucolymphocytosis [LCI 2018, Goldman 2009, Carbonetti 2015].
After an incubation time averaging 7-10 days (range 5-21 days), typical pertussis runs a three stage course (figure 1). It starts with nonspecific common cold-like symptoms and a slowly increasing cough lasting 1-2 weeks (catarrhal phase). Thereafter coughing becomes severe with copious mucus production and frequent expiratory paroxysms which often end with a profound inspiratory effort eliciting a sound called a “whoop”, often followed by post-tussive vomiting (paroxysmal phase, 3-8 weeks). However, in the youngest children and especially in premature newborns, typical symptoms may be absent; apnoeic and bradycardic episodes without whoops can be the dominant symptoms [Pasternak 1997]. Blood tests can show a very high leucocytosis, with a predominance of lymphocytes. In the third phase (convalescent phase 6-12 weeks), coughing slowly abates but can continue for many weeks to several months. While typical pertussis commonly manifests in immunenaïve individuals, symptoms of infection in vaccinated or previously infected individuals are atypical or mild and often not recognised as pertussis. “Pertussis-like” disease or cough can also be caused by B. parapertussis and other microorganisms such as Chlamydia pneumoniae, Mycoplasma pneumoniae and adenovirus. A clinical case definition aims to encompass all kinds of pertussis, using clinical, epidemiological and laboratory criteria [Senanayake 2007, Cherry 2005]: Coughing for at least two weeks combined with at least one of the following symptoms: inspiratory whoop, paroxysms, post-tussive emesis, apnoea and cyanosis (in the very young), or confirmed by one of the following laboratory results: culture, PCR or serology IgG-antiPT.
Complications
Five percent (5%) of individuals with classic pertussis develop complications. Complications are seen most frequently and are most serious in the very young (<6 months). More than half of children under one year old who develop pertussis require hospitalisation. Complications of otitis media or pneumonia can develop at any time during infection. Contrastingly, the most severe complications are seen during the paroxysmal phase: respiratory insufficiency and apnoea leading to convulsions and brain damage, subconjunctival haemorrhage, epistaxis, abdominal prolapses (hernia, rectum) and pneumothorax [Cherry 2005, Mattoo 2005, Skawronski 2003].
Epidemiology
Pertussis is an extremely contagious disease with a reproductive rate of 17 in an immune-naïve population. It is spread through coughing droplets containing B. pertussis. The milder the symptoms, the less contagious it is [Sch