PERTUSSIS Fiji National University

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PERTUSSIS Fiji National University Powered By Docstoc
					PERTUSSIS
        (aka) Whooping Cough
        An acute, communicable and lengthy (lasting about 6-8 weeks) respiratory illness that may
         affect susceptible persons of all ages, but is especially serious in young children.

Causative Agent
   Bordatella pertussis (less common is Bordatella parapertussis which causes a milder form of
     pertussis)
   Small, aerobic, non-motile Gram –ve coccobacilli.
   Fastidious organism – survives only a few hours in respiratory secretions and needs special
     media to be isolated and grown.

Transmission
    Humans are the only reservoirs of B. pertussis
    Bacteria spread by aerosolized droplets from coughing of infected individuals.
    Direct face to face contact, closed confined areas or exposure to the respiratory, nasal or oral
     secretions of an infected individual.
    Adults are usually an important source of B. pertussis infection among non-immunised or
     partially immunised children.
    Carriers of the infection are asymptomatic – not a significant source of infection because they
     are not coughing.

Pathogenesis




  B. pertussis may extend to infect the alveoli, but will never invade past the resp. Epithelium
   layers and is rarely found in the bloodstream (blood cultures are -ve for B. pertussis).
  Virulence factors and toxins released by bacteria enable its attachment to the resp. epithelium,
   local tissue damage to epithelium and cilia and some systemic effects.

Clinical
Pertussis typically presents with symptoms in 3 stages and is preceded by an asymptomatic
incubation period of about 7-10 days. 3 stages are:

Catarrhal Stage
    Lasts 2-7 days
    Non-specific signs and symptoms – similar to common cold
    Rhinorrhea, nasal congestion, sneezingFever – uncommon, but if present it is low grade
    Cough – which gradually increases instead of improving like that in an URTI
Paroxysmal Stage
Lasts 1-4 weeks
    Paroxysmal coughs (coughing episodes with increasing intensity) followed by a characteristic
       ‘whoop’ due to forceful inspiration of air through a narrowed glottis. About 10-30 rapidly
       successive coughs in an episode with almost 20 episodes in a day. Paroxysms are more
       frequent at night. Paroxysms may develop spontaneously or due to external stimuli, for
       example, exertion; feeding in infants
    Post-tussive vomiting – may lead to dehydration and nutritional compromise if not managed well
       or corrected.
    May develop cyanosis, gagging, protrude the tongue, with tearing, mucus and saliva from the
       eyes, nose and mouth.

Convalescent
   Cough paroxysms begins to subside – decreasing in intensity and frequency gradually over the
      next few weeks or even months.
   Duration of this stage varies
   Paroxysmal type coughing may occur for 6 or more months after the occurrence of pertussis, in
      association to other respiratory infections that may occur during convalescence.

Atypical Presentations
    Certain groups of persons do not present with typical pertussis. These include:
    Young infants (< 6 months)
    Previously immunised children
    Older children & adolescents – due to waning immunity

In young infants, presentation of pertussis may be different because of:
     A very short or absent catarrhal stage
     Early symptoms may include tachypnoea, difficulty feeding, or respiratory distress
     No characteristic ‘whoop’ at the end of a cough paroxysm – young infants don’t have very strong
        thoracic muscles which can enable the forceful inspiration which produces the whoop. Usually
        they appear to have an apnoeic episode, gagging and cyanosis after a paroxysm.
     May appear deceptively well, with no respiratory symptoms or signs between the cough
        paroxysms.

In previously vaccinated children, efficacy of the complete regimen of pertussis vaccines is not 100%,
putting them at increased risk of getting the infection compared to recently vaccinated children. They
may develop an atypical and milder form pertussis, not immediately fitting the CDC clinical case
definition of pertussis – with potential to miss these cases.

Diagnosis
    Typical pertussis – reliably diagnosed clinically, based on characteristic history and physical
       findings
    Atypical presentations – must have a high index of suspicion to make diagnosis
    Consider pertussis in children with a cough ≥ 14 days.

The CDC has clinical case, confirmed case and probable case definitions to help in diagnosing an
individual if having pertussis.

A clinical case definition is defined as a person:
Who has a cough illness lasting at least two weeks with one of the following:
    paroxysms of coughing,
    inspiratory "whoop," or
    post-tussive vomiting,
    and without other apparent cause (as reported by a health professional)
The laboratory criteria for diagnosis is defined as:
   The isolation of B. pertussis from a clinical specimen, or
   Positive polymerase chain (PCR) reaction assay for B. pertussis


A confirmed case is defined as a person:
    With an acute cough illness of any duration who is culture-positive from nasopharyngeal
      secretions
    Who meets the clinical case definition (see text) with laboratory confirmation by PCR from
      nasopharyngeal secretions
    Who meets the clinical case definition (see text) and is epidemiologically linked directly to a
      case confirmed by either culture or PCR from nasopharyngeal secretions

A probable case is defined as a person:
    Who meets the clinical case definition (see text) without laboratory confirmation or an
      epidemiologic link to a laboratory-confirmed case

Laboratory
    Leukocytosis – due to lymphocytosis (proliferation of lymphocytes). Profound lymphocytosis (>
     70% of WBC count). Usually develops at the end of the Catarrhal stage or during the
     Paroxysmal stage. Characteristic feature, but NOT diagnostic.

Other lab investigations to aid in confirming a diagnosis:
    Culture – B. pertussis may be isolated and cultured from nasopharyngeal secretions taken
       during the Catarrhal and early Paroxysmal stages. Important to perform lab testing as soon as
       diagnosis is considered as it is difficult to grow B. pertussis after the Paroxysmal period or
       after antibiotic treatment is initiated.
    Polymerase Chain Reaction (PCR) assay
    Direct Fluorescent Antibody (DFA) testing – use nasopharyngeal specimens to identify B.
       pertussis. Very useful if antibiotic treatment has been started as antibiotics decrease the
       likelihood of getting a +ve culture.
    Serology – ELISA – test depends on the demonstration of an increase in antibody titre, so not
       very useful in early diagnosis or stages of pertussis.

Complications
The complications from Pertussis most often affect the young infants:
    Apnea – almost occur exclusively in infants esp. < 6 months old. May occur spontaneously or
      in association with cough paroxysms and is possibly due to vagal stimulation.
    Pneumonia – may be a primary manifestation of pertussis (due to the extension of infection by
      B. pertussis to include the pulmonary alveoli) or a secondary bacterial infection. It may require
      hospitalisation
    Seizures
    Death – usually in young infants < 6 months of age, who are too young to have already
      completed their regimen of pertussis vaccinations
    Other complications may include: weight loss and dehydration (from feeding difficulties or
      post-tussive vomiting), epistaxis, facial petechiae, subconjunctival hemorrhage, fractured ribs,
      pneumothorax, inguinal or umbilical hernias, subdural hematomas (usually 2˚pressure effects
      from the Proxysmal stage).

Treatment
    Hospitalisation – especially with young infants, or on presentation of respiratory distress,
       cyanosis, apnea, seizures, inability to feed.

    Isolation – keeping patients isolated for at least 5 days after start of antibiotic treatment so as to
       prevent transmission of B. pertussis as it is very contagious.
    Supportive
          Monitoring respiratory status – providing oxygen, doing light suctioning for secretions,
              etc
          Fluid or nutritional support – to prevent any weight loss or dehydration due to the
              exertion on coughing, difficulty feeding and vomiting experienced.
          Avoiding stimuli that may trigger the cough paroxysms.

    Antibiotics:

Macrolides – interfere with RNA dependent protein synthesis in the bacteria.
  1. Erythromycin – drug of choice for infants. Given orally q6h for 14 days. The newer generation
      macrolides - Azithromycin and Clarithromycin - may be better tolerated.
  2. Azithromycin – favoured for use in infants < 1month old. Erythromycin is an alternative – but
      usually associated with development of Infantile Hypertrophic Pyloric Stenosis (IHPS) in
      infants < 1 month old. Clarithromycin not used.

    Co-trimoxazole - if the macrolides are contraindicated or not well tolerated. Given orally q12h for
       14 days. Not used in infants < 2 months old - they are at risk of bilirubin displacement and
       kernicterus.

Prevention
    Antibiotic chemoprophylaxis – for close contacts of the index case. Should be administered
       within 21 days of onset of symptons in the infected individual for better efficacy.
    Isolation during illness – prevents or reduces transmission to contacts as pertussis is contagious.
    Vaccination
            3 dose regimen in Fiji – given to infants at 6, 10, and 14 weeks old. Efficacy does not
               reach 100% and disease does not give lifelong immunity. Potential to still get infection
               and disease even if vaccinated.

				
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posted:4/9/2011
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