Whooping cough

Can be diagnosed if:

  • cough >2/52
  • coughing paroxysms present
  • no other cause identified

In young infants, adolescents, and adults, it can present as a single prolonged cough (references here and here). That complicates diagnosis considerably.

Note that it starts with coryzal/mild conjunctival symptoms and a mild cough. The cough becomes paroxysmal after 7 – 14 days. There is conflicting evidence (not listed) on the window of opportunity for antibiotics – it may be worth trying them as late as 8 weeks but others say 3 weeks. Macrolides would be the usual choice, but co-trimoxazole is an alternative in patients over two months. In the unlikely event of me treating a baby <1 month, I should use azithromycin as it’s the only macrolide not contraindicated at that age. Erythromycin or clarithromycin are 7/7, azithromycin 5/7.

No other treatments really help particularly with symptoms, with the exception of IV pertussis Ig in children (not clear whether it’s been tested in adults and found wanting or whether just not tested – I think the latter). It’s worth advising smoking cessation where relevant.

The incubation period is 5 days after antibiotics have been started – exclude children . If any close contacts have a cough, assume pertussis and treat as such. If contacts are unimmunised or partly immunised, advise they complete course as soon as possible. The article was a bit fuzzy on indications for post-exposure prophylaxis, but infants and pregnant women in the third trimester are at particular risk.

Culture of swab or NPA is most sensitive in the early stages and/or in unvaccinated individuals. After 3 – 4 weeks (according to BMJOnline – Pulse article says 2 weeks) anti-pertussis toxin IgG should be used for diagnosis. Pulse says serology rather than NPA should also be used if >48 hrs after starting antibiotics. A single IgG titre >100 – 125 Eu/ml is highly sensitive and specific.

Note that lymphocytosis is also typical. CXR may show changes (focal atelectasis or perihilar infiltrates) but these are not specific.

Note that immunity is not lifelong. If an unimmunised or partially immunised patient with a history of pertussis has been in contact with pertussis again, this is still an indication for immunisation (plus, of course, there’s the difficulty of being sure of the diagnosis).

Note that pneumonia is the most common complication. There are others, such as seizures or encephalopathy.

(Source – BMJ Online Learning module with some details from Pulse module)

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About Dr Sarah

I'm a GP with a husband and two young children.
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