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) for a week, 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 (2 weeks or more). 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. Note epidemiology below, 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).
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
- Malignant pertussis – rapidly progressive ARDS, pulmonary hypertension and right heart failure, multiorgan failure. Hyperleukocytosis is predictive (contributes to endothelial damage?) – increase of greater than 10 per day associated with death in PICU (but not absolute count), as is CRP>20. Hyperhydration contraindicated of course, so ECMO and leucodepletion have been attempted.
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. Mums appear to be the source in 38% of cases, dads in 17% of cases. That suggests that half the cases come from other family members of the community.
In low coverage areas burden of disease is in 5 yr olds, because of regular exposure through life.
Epidemiology
Before the vaccine era, there were often in excess of 100 000 cases of pertussis per year in England and Wales. Whole cell pertussis was effective but was associated with seizures and in rare cases long term brain damage, leading to a fall in vaccine uptake in the 70s and a resurgence in cases. The acellular vaccine has less side effects.
In 2012, national outbreak declared in UK on basis of higher than usual prevalence. Similar spike in numbers worldwide. New vaccination in pregnancy campaign, still on going – 90% effective against pertussis in babies, and disease less severe if infected. Antibody transfer to baby but also reduced chance of close contact. 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.
Cause for outbreak 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.
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
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.
48 hour isolation if treated, 21 days from onset if not.
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.
Prevention
“Cocooning” is the strategy of vaccinating a baby’s mother (AFTER BIRTH) and father (during pregnancy) to protect baby against pertussis. Considered cost effective although I can’t see any evidence… Tricky though, because getting dads/grandparents to vaccine appointments is harder than getting a mum at an antenatal appointment – and because any delay in vaccinating the mum after birth reduces the usefulness of the vaccine.
The US does both cocooning and vaccination in pregnancy, I believe.
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.