Organism: Bordetella pertussis Flashcards
Describe the epidemiology of pertussis
Highly contagious infection of the respiratory tract
may occur at any age but most severe in infants
endemic worldwide and periodic outbreaks occur
30% of adults with a cough lasting >2 weeks may have pertussis
Prior to the introduction of immunisation, epidemics occurred every 4-5 years, with the highest attack rate in young children
What leads to pertussis reinsurgence?
In recent years 🡪 increased numbers of cases including deaths especially in the very young
Reduced herd immunity – lack of natural boosting and waning immunity
Poor long term protective efficacy of acellular pertussis vaccines
Reinfection can occur
An additional booster is now recommended for which groups of people?
Children aged 11-14 years
Healthcare workers
What are the virulence factors?
- Filamentous haemagglutinin
- Pertactin (an outer membrane protein, P69 protein)
- Fimbriae
- Capsule
- Cytotoxin
- Pertussis toxin
- Endotoxin (LPS
How is pertussis diagnosed?
Clinical features
Microbiological tests
Culture – aspiration of nasopharyngeal secretions (in the very young) or nasopharyngeal swab – special transport medium – rapid transport to laboratory
Serology
Nucleic Acid Amplification tests (NAAT) – PCR – more sensitive than culture and faster
Other supportive lab tests
↑ WCC with absolute lymphocytosis
What is the laboratory diagnosis of pertussis
Culture (Fastidious organism)
Bordetella spp. do not enter the bloodstream
Blood cultures are of no benefit
Serology
Anti-pertussis IgG detected on samples taken > 2 weeks after onset of symptoms
More useful for epidemiological purposes
PCR
On pernasal swab or nasopharyngeal aspirate
Describe culture in the laboratory diagnosis of pertussis
Selective & enriched medium; (laboratory must be notified in advance)
Charcoal-blood agar, antibiotics to inhibit normal flora, may take up to 10 days to grow
Gram negative coccobacilli (tiny)
Lacks sensitivity
What are the laboratory features of pertussis?
Very small Gram negative cocco-bacillus 3 distinct serotypes 1-3 Human specific organism Strictly aerobic Capsulated
Give the pathogenesis of pertussis
Portal- Inhalation of droplets
Attachment to respiratory mucosal cells- Filamentous haemagglutinin (ciliated cells)
-Pertactin (P69 protein) (tracheal cells)
- Fimbriae (ciliated cells)
Evasion- Capsule
Damage- Cytotoxin- paralyses cilia, causes paroxysms of coughing
-Pertussis toxin
-Endotoxin (lipopolysaccharide)- causes disruption of the host cell
How is Whooping cough spread?
Shed in respiratory droplets with coughing or sneezing
The organisms attach to ciliated respiratory epithelium in the nasopharynx and trachea
They resist innate defences - mucociliary clearance, antimicrobial peptides, and multiply and resist phagocytosis
Bronchioles become blocked with inflammatory cells, lymphocytes & mucous
Bronchiolar obstruction leads to collapse of alveoli, resulting in diminished oxygenation of the blood
What measures have been taken to ensure the prevention of pertussis?
Universal infant immunisation is recommended
(WHO and National agencies)
Whole cell pertussis vaccines were used in the past
Suspension of killed organisms
Acellular vaccines are now generally used
Contain antigen to 3 or more virulence determinants
Significantly fewer local/systemic reactions than observed with whole cell vaccine
Administered in combination with diphtheria and tetanus vaccines (DPT, “Triple Vaccine”)
Ireland: 3 doses (2, 4, 6 months), boosters (4-5 years and adolescence)
Describe the treatment of Whooping cough
Primarily supportive, e.g., fluid administration
Erythromycin / clarithromycin
if administered in the catarrhal stage may eliminate the disease, & may prevent transmission
Hospitalisation & ICU care may be required in the very young
What are the stages of Whooping cough?
> Catarrhal Stage 1-2 weeks
*Nonspecific symptoms e.g., generalised malaise, rhinorrhoea, and mild cough:
*The most infectious stage
Paroxysmal Stage 2-4 weeks
*Paroxysmal cough - severe, vigorous coughs that occur during a single expiration following by vigorous inspiration * whooping sound
*Post-tussis vomiting
Convalescent Stage 3-4 weeks
gradual reduction in the frequency and severity of cough
The total duration of all three phases is typically about three months
State the pertussis complications
Condition Percent reported Pneumonia 5.2 Seizures 0.8 Encephalopathy 0.1 Death 0.2 Hospitalization 20 *Highest mortality rate is in preterm infants *Pneumonia in 20% of infants
Describe pertussis in adults
up to 7% of cough illnesses per year in adults are pertussis
20-30% of cough illnesses in adults lasting >14 days are due to pertussis
Milder than in infants & children
Typically under-recognised
Adults are often the source of infection for children
