Bordetella pertussis: Clinical manifestations and diagnosis

Introduction

• Whooping cough is caused by B. pertussis.
• < 5% cases it is caused by B. parapertussis.
• No cross immunity of B. pertussis with B. parapertussis:
• antibodies against B. Pertussis do not protect against B. parapertussis.
• More cases occur during winter and spring month, due to overcrowding.

Source of infection:

• Case of pertussis (not carrier).
• There is no subclinical case
• Chronic carrier state does not exist.

Infective period:

• Catarrhal stage.
• The infective period extends from a week after exposure to about 3 weeks after the onset of the paroxysmal stage.

Secondary attack rate :

• High, i.e. 90%.

Age group:

• Disease of infants and young children (< 5 years of age).
• Infants are susceptible to infection from birth because maternal antibody does not give them protection.
• Mean age of infection is between 2 0- 3 0 months.
• However, it can also affect, though less commonly, older children, adolescents and adults.

Sex predisposition in pertussis:

• Incidence and fatality are more among female than male children.

Infective material:

• The infective bacilli occur abundantly in the nasopharyngeal and bronchial secretions.
• Objects freshly contaminated by such discharges are also infective.

Mode of transmission:

• By droplet infection and direct contact.
• The role of fomites in the spread of infection appears to be very small, unless they are freshly contaminated.

Clinical features

• After an incubation period of about 1-2 weeks
• Disease takes a protracted course comprising three stages”
• Catarrhal, paroxysmal and Convalescent
• each lasting approximately two weeks. 

Catarrhal stage:

•  Infectivity is maximum.

Paroxysmal stage: –

• Post-tussive vomiting
• Mucus Plug.
• Vomiting with cough.
• Episodes are often worsened at night and interfere with sleep.
• Most complication occur during paroxymal stage.
• Paroxysm is precipitated by noise, eating and physical contact
• Leukocytosis due to absolute lymphocytosis is characteristic in late catarrhal or paraoxysmal stage

Convalescent stage

Complications of Pertussis

• Subconjunctival haemorrhage, Intracranial haemorrhage
• Severe malnutrition

• Presence of recurrent bouts of severe cough followed by an audible whoop suggests a diagnosis of pertusis.
• Culture of nasopharyngeal secretions remains the gold standard of diagnosis.
  
• Best specimen is collected by nasopharyngeal aspiration.
• An alternative to the aspirate is a Dacron or rayon nasopharyngeal swab. 
• DNA detection by polymerase chain reaction (PCR) increased sensitivity and quicker results.

Lymphocytosis

• A peculiar feature of Bordetella infection is “lymphocytosis” (lymphocytosis is unusual in bacterial infections).
• M bordetella an absolute lymphocyte count of >10 x 109/L is common among young children
• Manifests in the blood as a mature lymphocytosis. 
• Lymphocytes often have a weird “clefted” appearance”

Exam Question

 

Introduction

• Whooping cough is caused by B. pertussis.
• < 5% cases it is caused by B. parapertussis.

Source of infection:

• Case of pertussis (not carrier).

Secondary attack rate :

• High, i.e. 90%.

Age group:

• Disease of infants and young children (< 5 years of age).
• Infants are susceptible to infection from birth because maternal antibody does not give them protection.

Mode of transmission:

• By droplet infection and direct contact.
• The role of fomites in the spread of infection appears to be very small, unless they are freshly contaminated.

 lncubation period:

7 – 14 days.

Clinical features 

Catarrhal stage:

•  Infectivity is maximum .

Paroxysmal stage: –

•  Post-tussive vomiting
• Mucus Plug.
• Vomiting with cough.
• Episodes are often worsen at night and interfere with sleep.
• Most complication occur during paroxymal stage.
• Paroxysm is precipitated by noise, eating and physical contact
• Leukocytosis due to absolute lymphocytosis is characteristic in late catarrhal or paraoxysmal stage

Convalescent stage

Complications of Pertussis

Respiratory –

• Patchy Atelectasis
• Subcutaneous emphysema

Neurological-

• Persistent seizures
• Paraplegia 
• Ataxia: Not of cerebellar origin. There is no involvement of the cerebellum in Pertusis

Diagnosis:

• Presence of recurrent bouts of severe cough followed by an audible whoop suggests a diagnosis of pertusis.
• Culture of nasopharyngeal secretions remains the gold standard of diagnosis.
  
• Best specimen is collected by nasopharyngeal aspiration.

DNA detection by polymerase chain reaction (PCR) increased sensitivity and quicker results.

Lymphocytosis

• Lymphocytes often have a weird “clefted” appearance”