Protracted Bacterial Bronchitis (PBB)
Anne B Chang1,2
1
Queensland Children’s Respiratory Centre and Queensland Children’s Medical Research
Institute, Royal Children’s Hospital, Brisbane;
2
Child Health Division, Menzies School of Health Research, Darwin;
Prof Anne Chang
Queensland Children’s Respiratory Centre
Royal Children’s Hospital, Brisbane, Herston, Queensland 4029, Australia
Tel: 61 7 36365270 Fax 61 7 36361958
Email: annechang@ausdoctors.net
What is PBB?
PBB, long been recognized by pediatric pulmonologists worldwide, was only adequately
characterized (clinically and BAL) recently.1-3 PBB’s original description was derived from a
prospective study that evaluated the aetiology of chronic cough in children using a research
protocol. The study1 used a priori defined criteria and validated cough diaries to assess
response with a clear time period relating to when medications were given. In the 108 young
children with chronic cough in the study, bacterial infection of the airways (defined as growth
of single pathogens of ≥105 cfu/ml) was the most common (40% of children) finding.1 Airway
neutrophilia was also present and the respiratory pathogens found in the endobronchial
infection were H influenzae, S pneumoniae and M catarrhalis.1,3 The criteria for PBB in the
research study were; (1) history of chronic moist cough, (2) positive BAL culture, and (3)
response to antibiotic treatment with resolution of the cough within two weeks.
Outside of research protocols, bronchoscopies cannot be routinely undertaken for
uncomplicated chronic wet cough in clinical practice. Thus PBB, sometimes truncated to
protracted bronchitis (PB) is clinically defined as (a) the presence of isolated chronic (>4
weeks) wet/moist cough, (b) resolution of cough with antibiotic treatment and (c) absence of
pointers suggestive of an alternative specific cause of cough.2 Hence while the diagnosis of
PB can be suspected at the time of consultation, it can only be made down the track on
review. PB has been officially recognized by the Thoracic Society of New Zealand and
Australia and the British Thoracic Society.2
The clinical profile of children with PB
Children with PB are typically young (<5 years of age, median age-3years1,3), do not have any
other systemic symptoms including the absence of clinical sinusitis and ear disease. Some
parents may report a ‘wheeze’ but it usually represents a misinterpretation of the sound.3
Many of these children have been misdiagnosed as having asthma.1,3 Their chest x-rays
usually show peribronchiolar changes or may be reported as ‘normal’.1,3 Like children with
chronic cough, children with PB have significant morbidity; parents typically have seen
multiple medical practitioners for their child’s chronic cough in the last 12 months. In PB the
child’s cough resolves only after a prolonged course of appropriate antibiotics (12-14 days).
When a typical course (5 days) of antibiotics is used, the cough either relapses within 2-3
days, or slightly subsides but does not resolve completely. This is in contrast to the short
course of antibiotics (5-7 days) required to treat community acquired pneumonia in otherwise
well children. Children with PB also have higher Canadian Acute Respiratory Infection Scale
(CARIFS) scores in subsequent respiratory illness. When compared with children with acute
asthma and normal controls, children with PB, there was no difference between groups on
day-1. However days 7, 10 and 14 later, children with PB had significantly (p <0.0001 for all)
higher CARIFS scores.2
Pathogenesis of PBB
PBB is associated with persistent bacterial infection in the airways1,3 and it is widely accepted
that persistent bacteria infection (with accompanying inflammation) is harmful to the airways.
PBB is likely non-homogenous with neutrophilic airway inflammation developing by a
variety of mechanisms. It is likely that an innate immune dysfunction or immature adaptive
immunity is present, at least in a subgroup of these children. A group of children with
bacterial colonisation, airway neutrophilia and protracted cough that was unrelated to the
presence or absence of oesophagitis, was identified from 150 children undergoing
gastroscopy.4 In children without lung disease, cough was more likely to result from airway
bacterial infection and not to esophagitis.4 The abnormal microbiology of the airways in
children with cough, was not reflected in the microbiology of gastric juices. In a subset of
these children (n=69), bacterial colonisation of the lower airways was associated with
neutrophilic inflammation and reduced expression of both the toll-like receptor (TLR) -4 and
the preprotachykinin gene, TAC1, that encodes substance P.5 Substance P has a defensin-like
function which may explain the association between reduced TAC1 and persistent bacterial
infection. In order to provide additional evidence for a dysfunctional host response to
bacterial infection, chemokine receptor expression was assessed. Elevated gene expression for
neutrophil chemo-attractant chemokine IL-8 cellular receptor, CXCR1, was detected, while
the chemokine receptors (CCR3, CCR5) were similar between groups.
In another cohort of children with established chronic cough who presented to respiratory
physicians and had PBB, intense neutrophilic airway inflammation with marked inflammatory
mediator response (IL-8, active matrix metalloproteinase 9 [MMP-9]) was present, compared
to controls.6 The median levels of IL-8 (0.69, IQR 0.30, 1.72 ng/ml) in the BAL was similar
to those found in other studies that examined chronic airway inflammation in cystic fibrosis
and other forms of chronic suppurative lung disease.6 In contrast to above data, TLR-2 and
TLR-4 mRNA expression were significantly elevated in this cohort when compared to the
control group.6 However when corrected for neutrophil numbers (it remains unclear if values
should be corrected), TLR-2 and -4 were reduced.6 Furthermore when followed up those with
recurrent PBB has significantly reduced TLR-2 and 4 mRNA expression (adjusted values)
compared to those who had did not have recurrent PBB in the 12-mo follow-up period
(unpublished). Nevertheless there were other differences between these cohorts that include
age (innate immunity is age-dependent), duration of cough and key presentation history.
Thus the nature and duration of innate immune dysfunction remain undefined, nor is it clear
whether the dysfunction is specific to the lower airways or is more generalised (ie systemic).
Only a long term study will elucidate the pathogenesis and evolution of PB in children.
Treatment and follow-up of children with PB
Both the Australian and UK groups have described the response of the wet cough to a
prolonged (at least 2 weeks) course of antibiotics.1-3 In a Cochrane review (albeit consisting of
2 limited studies with total number of 140 children), chronic wet cough in children responded
to antibiotics with a number needed to treat of 3 (95%CI 2, 4) and the progression of illness,
defined by requirement for further antibiotics, was significantly lower in the antibiotic group
with a number needed to treat for benefit of 4 (95%CI 3, 5).2 However until a double blinded
randomized control trial that specifically addresses this question is performed, it remains
indefinite which children with wet cough should receive antibiotics.
Children with PB may have recurrent episodes. In the Brisbane cohort’s preliminary study,
approximately 35% of children have recurrent (> 2 episodes a year) PB. Also whether PB is
antecedent to chronic suppurative lung disease and bronchiectasis in some children is
unknown and important to evaluate. It is likely that, at least in a small but significant number
of children, PBB is an early spectrum of the same process leading to chronic suppurative lung
disease and bronchiectasis.2 Children with PB do not have established bronchiectasis as those
with established bronchiectasis usually have a different clinical profile and are unlikely to
recover after 12-14 days of oral antibiotics. It is suggested that children with recurrent PB (>2
episodes per year) are evaluated like a child with bronchiectasis.
Summary
In summary, chronic wet cough in young children is common and causes considerable
morbidity and health care costs. A clinical diagnostic entity called PBB is the most common
cause of chronic wet cough on young children. Even though many children with PBB get
better with 2 weeks of antibiotics, the long term consequences in young children whose
pulmonary system are still developing, remains undefined. In published preliminary studies,
reduced levels of receptors involved in innate immune recognition in the BAL cells of
children with PBB and airway infection were described. It is likely that, at least some if not
many, children with recurrent PBB have innate immune dysfunction and are at risk of chronic
suppurative lung disease, which has been lately recognised to be not as rare as previously
thought. Studies elucidating the determinants of chronic airway inflammation and bacterial
colonisation in children, in particular the role of innate immunity dysfunction in children with
recurrent PBB and their clinical outcomes are required.
References
(1) Marchant J M, Masters I B, Taylor S M, Cox N C, Seymour G J, Chang A B.
Evaluation and outcome of young children with chronic cough. Chest 2006; 129:
1132-1141.
(2) Chang A B, Redding G J, Everard M L. State of the Art - Chronic wet cough:
protracted bronchitis, chronic suppurative lung disease and bronchiectasis. Pediatr
Pulmonol 2008; 43: 519-531.
(3) Donnelly D E, Critchlow A, Everard M L. Outcomes in Children Treated for
Persistent Bacterial Bronchitis. Thorax 2007; 62: 80-84.
(4) Chang A B, Cox N C, Faoagali J, et al. Cough and reflux esophagitis in children: their
co-existence and airway cellularity. BMC Pediatr 2006; 6: 4.
(5) Grissell T, Chang A B, Gibson P G. Impaired toll-like receptor 4 and substance P gene
expression is linked to airway bacterial colonisation in children. Pediatr Pulmonol
2007; 42: 380-385.
(6) Marchant J M, Gibson P G, Grissell T V, Timmins N L, Masters I B, Chang A B.
Prospective assessment of protracted bacterial bronchitis: airway inflammation and
innate immune activation. Pediatr Pulmonol 2008; 43: 1092-1099.