Pertussis

Whooping cough, caused by Bordetella pertussis. B parapertussis can cause similar illness but usually less severe. B. holmesii also seen.

Classically, Catarrhal phase (mild fever, productive cough, no pharyngitis) then Paroxysmal (coughing fits, often associated with vomiting, followed by characteristic inspiratory “whoop”) then Convalescent – persistent cough, traditionally 4-12 weeks (100 days)! Fever is rare, and in fact patients can often look relatively well between paroxysms, with clear chest and no respiratory signs. Young infants may present with apnoea rather than whooping.

Post tussive vomiting is pretty specific in adults, but only 66% in children.

Adult disease presents in its mild form as disturbed sleep, sweating, sinusitis or otitis, protracted cough so not usually diagnosed. Cough associated with choking is characteristic, whereas sweating is not very sensitive or specific. Cough is non-productive (although there may be a sensation of retained secretions – question carefully!).

But probably underdiagnosed, esp where symptoms are chronic but mild, or in the third of cases where symptoms last less than 3 weeks.

In UK children aged 5-15 with persistent cough (ie over 14/7, in many cases severe) identified in primary care, at least 20% had evidence of recent infection with Bordetella pertussis,  (doi:10.1136/bmj.g3668) Hence reported incidence depends on quality of surveillance rather than actual prevalence! Probably the same everywhere, with peaks every 2-5 yrs.

The reason for the chronic, persistent cough is still not clear (many infections cause similar ciliary disruption, and don’t cause such chronic symptoms).

In 2012, national outbreak declared in UK on basis of higher than usual prevalence.  New vaccination in pregnancy campaign, still on going.  Cause uncertain: more sensitive diagnostic methods?  Enhanced awareness and reporting?  Less enduring protection after immunization with acellular vaccines (cf whole cell vaccines)? Mismatch between antigens in acellular vaccines and circulating strains of B pertussis? Although the largest increase in reported incidence seems to be in adolescents, children aged <3 months are at highest risk of serious morbidity and mortality from pertussis.

Complications

  • Rarely encephalopathy, including seizures. Probably a direct toxin effect, plus hypoxia during paroxysms.
  • Hernias and rectal prolapse.
  • Secondary pneumonia is not uncommon, so if chest signs are present consider antibiotic treatment to cover other organisms.
  • Pneumothorax, aspiration, rib fractures in elderly
  • Sinusitis, otitis

Immunity

Although part of universal immunization schedule, immunity (from immunization or exposure) is pretty short lived viz 2-5yrs, so in vaccinated areas severe disease seen either pre-immunization ie young babies, or adolescent/adults after immunity has worn off. Most cases in unvaccinated infants are contracted from a family member, usually the mother. In low coverage areas burden of disease is in 5 yr olds, because of regular exposure through life. Currently programme vaccinating pregnant women – appears to be safe.  Another strategy by which susceptible infants can be protected—cocooning—involves immunizing all close contacts of the infant, not just the mum.  Both approaches have been shown to be cost effective, the US does both.  Other countries boost teenagers.  Better vaccines would be nice! WHO recommends that countries still using whole cell vaccines continue to do so unless they can schedule boosters. See Vaccines.

Diagnosis

Notifiable!

  • Lymphocytosis can be spectacular but not sensitive. Due to Pertussis toxin, as used in vaccine, which is specific to B pertussis but probably not that important for pathogenesis cf tracheal cytotoxin etc. Hence not seen post immunization (ie adults), in parapertussis, or in neonates (transplacental antibodies).
  • Culture from pernasal swab is not fantastically sensitive but is useful for genetic studies. False negatives mostly due to sampling late in course of disease.
  • PCR more sensitive than culture but false positives common (as usual with PCR).
  • Numerous different ELISA tests � be suspicious of any that are qualitative (pos/neg) rather than quantitative. IgG based are good, whole cell tend to be poor. Mouth swab test available.
  • Serology is of limited use for infants (transfer of maternal IgG), but you can always test the parents (Mum may have stored serum from pregnancy).

Differential

Asthma!  Cystic fibrosis.

Mycoplasma and adenovirus can cause chronic cough.

Treatment

48 hour isolation, 7/7 erythromycin or clarithro, 3/7 azithro. Clarithromycin preferred in neonates, given association with pyloric stenosis (may also be a risk with azithro).  Co-trimoxazole as second line.  Makes little difference to clinical course, but does help reduce transmission. Treat within 3-4 weeks of start of illness. Azithromycin  is as effective as erythromycin, gastrointestinal adverse events are much less, and compliance in general was markedly better [Pediatrics. 2004 Jul;114(1):e96-101 – pmid:15231980].

Still need full immunization course as natural disease does not confer long lasting immunity.

Prophylaxis

Where vulnerable individuals eg unimmunized infants, asthmatics are exposed to a likely case, there is an argument for giving prophylactic erythromycin to all close contacts. See Health Protection Agency advice. Journal of Public Health Medicine 2002;24(3):200-206.

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