Pus has received written commentary since the first recorded medical works. Prescriptions for draining pus from abscesses were found in the Egyptian Medical Papyri (1550 BC) (2) and Hippocrates (430 BC) described empyema in several of his writings (3, 4). By the early 1800s, bronchiectasis, empyema, and lung abscess were recognized clinical entities associated with purulent secretions noted on autopsy but not yet linked to infection (5). In the latter half of the nineteenth century, the association of bacteria and infection with these entities evolved. In the 1870s, Pasteur reported that microorganisms were found in pus and were necessary to cause purulent infections (6). By the end of the nineteenth century, textbooks of bacteriology classified the “pyogenic bacteria” (Staphylococcus aureus and Streptococcus pyogenes), and noted that the most common cause of lobar pneumonia was pneumococcus (7). In the first quarter of the twentieth century, before the development of antibiotics, radiographic imaging became a standard diagnostic tool, which revolutionized the diagnosis of pneumonia, lung abscess, and pleural disease (8). In the 1800s, bronchiectasis was most often associated with sequelae of then common infectious diseases, including pertussis, measles, and tuberculosis, or due to the long-term effects of retained airway foreign bodies (9). Over the past 50 years, with the advent of vaccinations, improved nutrition, public health services, environmental awareness of indoor pollutants, and antibiotics/antifungal therapies, the prevalence of bronchiectasis has significantly decreased. It is now considered relatively uncommon in developed countries, though it still remains a significant cause of morbidity.

The common themes of the suppurative pulmonary conditions are persistent and recurrent infection, intense neutrophilic inflammation, and poor clearance of infected material. Classic suppurative lung diseases are characterized by pus observed in expectorated sputum or sampled with drainage procedures through pleural catheters and with bronchoalveolar lavage.

Persistent inflammation becomes destructive but is often compartmentalized to a lung region. Lung abscesses are usually thick-walled localized regions; bronchiectasis, even in children with CF, occurs with only patchy peribronchiolar pneumonitis and could be considered an endobronchial abscess (10). Sepsis rarely occurs in children as a consequence of lung abscesses or bronchiectasis.

Bronchiectasis is defined by the abnormal appearance of the conducting airways by high-resolution computerized tomography (HRCT) of the chest, producing dilation, thickened airway walls, and saccular changes in the clinical setting of chronic wet cough with or without expectoration of mucopurulent sputum. Bronchiectasis can be diagnosed in some chest radiographs, but this is an insensitive way to make the diagnosis and is not considered the gold standard. Bronchiectasis is the result of chronic airway infection leading to loss of structural integrity of the airway wall, which produces airway dilation. It can occur focally after serious acute respiratory infections or with post-obstructive pneumonia due to foreign body or endobronchial lesions (tumor and tuberculosis) or throughout the lung in a patchy distribution (e.g., CF and PCD). Bronchiectasis can also develop after severe lower respiratory viral infections, especially in indigenous populations (18, 30). Bronchiectasis results in airway dilation, described as cylindrical or saccular in shape, diagnosed by HRCT. The relatively increased size of the airway lumen compared to its neighboring pulmonary artery produces a “signet ring” appearance, diagnostic of bronchiectasis. However, the normal ratio of the airway to the vessel diameter is age dependent in normal children (31).

Protracted bacterial bronchitis is a recognized entity encountered primarily in young children. It is defined by a “wet” cough lasting longer than 1 month. It is likely a precursor to bronchiectasis in some cases, but it can be completely eliminated with two to three prolonged courses of antibiotic treatment (32). Children with PBB are often too young to expectorate sputum even though they present with a “wet” cough. Only through clinical studies using samples obtained by bronchoscopy with bronchoalveolar lavage do we know that this condition is characterized by neutrophil-rich sputum that is culture positive for bacterial pathogens (33).

Chronic suppurative lung disease (CSLD) is a broad descriptive term, but it has recently been specifically applied to children who clinically appear to have bronchiectasis but do not demonstrate the diagnostic imaging features of bronchiectasis. Children with CSLD respond to the same treatment regimens used for childhood bronchiectasis, and some authors consider them a spectrum of the same disorder. Of note, they differ from children with PBB in that their conditions cannot be completely reversed with multiple courses of antibiotics. In a 2-year prospective study, 43% of 161 children with PBB had >3 episodes of wet cough per year despite antibiotic treatment (32). The number of treatment failures that constitutes a change in diagnosis from PBB to CSLD has not been defined. Thirteen percent of children with PBB eventually demonstrated radiographic evidence of bronchiectasis (32). PBB and CSLD likely represent a continuum of chronic suppurative airway disease and recurrent treatment “failure” of children with PBB should raise the question of CSLD or bronchiectasis.

There remain glaring disparities among children in different societies who are at risk for CSLD. Access to vaccines for Haemophilus type b, pneumococci, and influenza, and comprehensive longitudinal health care vary significantly across and within countries. Among wealthy nations with effective public health infrastructures and proactive well-child care, suppurative lung disease is uncommon and usually occurs in the context of a known pulmonary or immune host defense disorder. However, among high-risk indigenous groups in Australia, New Zealand, Argentina, and Alaska, postinfectious bronchiectasis is most common. There is ongoing debate about the relative role of social and environmental risks versus immune deficiencies and abnormal lung injury and repair processes in different populations of children (16, 34, 35). It is of interest that a high rate of consanguinity has reported in several series of families whose children have idiopathic bronchiectasis, suggesting a genetic predisposition to bronchiectasis in some groups (36, 37).

The global burden of CSLD in children is unknown. The geographic prevalences of bronchiectasis are limited due in part to lack of access to imaging technology need to make the diagnosis. Those regions where prevalences of acute pneumonia, tuberculosis, HIV infections, malnutrition, and tobacco and biomass combustion are highest are likely to be the regions where CSLD is more frequent. Figures 1–5 depict the variations in frequencies of risk factors across countries and geographic regions. The world map of episodes per child year of acute pneumonia reported in 2007 is depicted in Figure 1 (38). Figure 2 is a map of worldwide cigarette consumption (# cigarettes smoked per person per year for individuals >15 years of age) according to the Tobaccos Atlas in 2015 (39). The percentage of households using solid fuel (biomass) for cooking in 2000 is depicted in Figure 3 (40). Figure 4 illustrates the global percentage of children <5 years old in 2005 who are underweight, a reflection of malnutrition (41). If these maps are superimposed, the highest risk for CSLD in children would occur in Southeast Asia, China, and Sub-Saharan Africa. Prevalence data about persistent suppurative lung conditions in children in most of these areas have not been reported.

Tuberculosis in children with and without HIV is also global concern. Several reports of chest CT findings in children with tuberculosis describe bronchiectasis occurring in 9–20% and cavitary lesions in 25% of adolescents (42, 43). The Global Tuberculosis Programme at the World Health Organization estimated that 1 million children developed tuberculous disease in 2014 (44). Seventy-five percent of children with tuberculosis come from just 22 countries. Of these, India alone accounts to 27% of the global burden of tuberculosis in children <15 years of age (45). The global frequency of tuberculosis cases per 100,000 population in 2007 is portrayed in Figure 5 (46). The map of HIV disease prevalences also compiled by the World Health Organization in 2007 is portrayed in Figure 6 (47). These maps suggest that bronchiectasis related to tuberculosis and HIV occurs most frequently in Africa, India, and parts of Southeast Asia.

Most children with acute suppurative processes, e.g., pneumonia, empyema, abscess, if treated appropriately, make full recoveries with minimal long-term morbidity. However, apart from CF, the long-term consequences of CSLD in children have not been well described. Serial lung function trends for children with CF and non-CF postinfectious bronchiectasis have been reported (48). Non-CF bronchiectasis is associated with worse lung function early in life soon after the initial airway injury, but it progresses much more slowly over time compared to CF-related bronchiectasis. Complete resolution of symptoms among Native Alaskan children with postinfectious bronchiectasis occurs in one-third by adolescence (49). Although the mortality risk is greater in adults with bronchiectasis than among adults with asthma, it is lower compared to adults with COPD, at least in developed countries (50). Among adults with COPD, mortality is higher when it bronchiectasis is also present. Systems of care that transition youth and young adults with CSLD to adult providers have been best developed for patients with CF and, more recently, for those with ciliary disorders. Comprehensive care models of non-CF-related bronchiectasis have been developed that stabilize and/or improve lung function over time (51). However, the impact of smoking tobacco and other combustible products among adolescents and young adults with bronchiectasis has not been reported. Also, these models have not accounted for eventual transitions to adult care.

With the advent of antibiotics, improved nutrition, and focus on child health in developed countries, bronchiectasis has been termed an “orphan disease.” Relative to the research devoted to CF, the published research on care of children with other chronic suppurative respiratory disease is scarce. Although the World Health Organization has prioritized asthma, acute pneumonia, and tobacco use, the burden of CSLD in children is unknown. Given the geographic distribution of risk factors worldwide, it is likely that children with these conditions are underdiagnosed and undertreated. The global burden of CSLD in children and its impact on health in adulthood are important to ascertain. Only then can effective systems of comprehensive longitudinal care in the context of different cultures be devised.

GR wrote entire article except history section. EC wrote history section and reorganized the article into current format.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.