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pertussis

pertussis (whooping cough)

introduction

  • pertussis is caused by a bacteria Bordetella pertussis
  • it is extremely infectious and not only causes 10-30% of all subacute coughs, but can be fatal in high risk patients such as infants
  • vaccination is partly protective but very important in reducing spread, all children should be vaccinated unless there are C/I, and likewise adolescents and adults should have a booster as immunity wanes by 10yrs

clinical features

  • incubation period is typically 7–10 days (range of 4–21 days)

initial catarrhal stage

paroxysmal stage

  • after 1-2 weeks, a paraoxysmal dry cough develops which can last months, and in children, often develops the classical whooping cough, or may just have post-tussive vomiting or syncope
  • FBE may show lymphocytosis

Dx

  • diagnosis is often clinical by the time the paroxysmal stage develops, and unfortunately, little can be done at this time as after 3wks of illness, starting antibiotics will have little benefit
    • after the 1st 3wks, consider pertussis serology to diagnosis cases of subacute cough:
      • “pertussis-specific IgA is only produced after natural infection, whereas IgG rises with vaccination and natural infection. While a positive IgA test confirms the diagnosis of pertussis, a negative result does not exclude the possibility of infection. (It is important to remember that a small proportion of the population has an IgA deficiency.) Paired samples showing rising titres of specific IgA or IgG are a more reliable indication that the patient has pertussis.”
  • those in contact with known cases of pertussis or contacts with subacute coughs, should be considered for nasopharyngeal swab for PCR (BEFORE antibiotics) and empirical antibiotics in the catarrhal stage to reduce infectivity
    • this is particularly important for healthcare workers, last trimester pregnancy, contacts with children under 2yrs who are not fully vaccinated, such as child care workers

Rx

  • close contacts
    • consider antibiotic prophylaxis of close contacts, particularly if there are un-immunised infants at risk
  • if in 1st 2wks:
    • nasopharyngeal swab for PCR, preferably before starting antibiotics
    • empirical antibiotics1):
      • azithromycin 10mg/kg (up to 500mg) daily for 3 days, or,
      • azithromycin 10mg/kg (up to 500mg) day 1, then 5mg/kg (up to 250mg) daily for next 4 days, or,
      • clarithromycin bd for 7 days, or,
      • co-trimoxazole bd for 7 days if the above are not tolerated
    • patients should avoid contact with susceptible individuals until at least five days of antibiotics have been taken
  • if after 3rd week:
    • antibiotics, steroids, asthma Rx, antihistamines are of NO benefit (unless patient also has asthma in which case asthma Rx should be continued if one believes the symptoms are asthmatic and not pertussis cough)
    • if Dx is not clear, consider pertussis serology as outlined in Dx section
pertussis.txt · Last modified: 2016/07/14 19:15 by gary1