Complications and long-term impact of early-life acute lower respiratory tract infections

INTRODUCTION

Lower respiratory tract infections (LRTIs) remain a leading cause of morbidity and mortality in children worldwide.^[1] Despite advances in prevention and treatment, their long-term pulmonary sequelae are increasingly recognized.^[2] Survivors of severe childhood LRTIs are at risk of developing chronic respiratory conditions, including asthma, bronchiectasis, and chronic obstructive pulmonary disease (COPD).^[3]

This is a narrative review of literature drawing from studies published between 1995 and 2025, including both high-income and low- and middle-income country (LMIC) cohorts. Diagnosis of pneumonia from included studies was based on clinical features (e.g., cough, fever, and tachypnea), radiological evidence, or microbiological confirmation, depending on the study design. For this review, “early life” refers to the first 3 years of life, a critical period for lung development, immune programming, and vulnerability to infection.^[4] Articles were selected based on relevance to long-term respiratory outcomes following clinically or radiologically confirmed LRTIs, including pneumonia and bronchiolitis.

PATHOGEN DIVERSITY AND EARLY-LIFE INFECTIONS

The spectrum of pathogens in childhood pneumonia is broad, ranging from bacteria such as Streptococcus pneumoniae to atypical organisms such as Mycoplasma pneumoniae and respiratory syncytial virus (RSV) has also been implicated.^[5,6] M. pneumoniae has been associated with both acute and chronic complications, including wheezing and asthma overlap.^[7] Maternal exposures, including human immunodeficiency virus (HIV) infection, smoking, and cytomegalovirus (CMV), have been shown to significantly impair infant lung function in LMICs.^[8] In one study, 14 of 18 children aged 7–8 years with airway obstruction had documented Chlamydia pneumoniae infection during infancy, suggesting a possible link between early infection and long-term respiratory compromise.^[9] Adenovirus infections have also been linked to chronic lung disease (CLD) outcomes.^[10] More recently, COVID-19 has emerged as a novel viral threat, with evidence suggesting potential long-term respiratory outcomes in children.^[11,12]

INFLAMMATORY PATHWAYS AND SEQUELAE

Persistent airway inflammation, impaired lung growth, and remodeling drive long-term sequelae. Children with recurrent pneumonia or severe early-life infections often show reduced lung function later in life. The Perth cohort^[13] demonstrated that childhood pneumonia was associated with impaired lung function persisting into adulthood. Findings from the Drakenstein cohort^[8,14] showed that early childhood wheezing phenotypes, influenced by RSV infection and maternal smoking, were associated with impaired lung function trajectories.

SOCIOECONOMIC AND ENVIRONMENTAL INFLUENCES

Premorbid health conditions influence disease severity and long-term outcomes, yet many studies overlook them.^[15] Children living in environments with high pollution levels, poor nutrition, and prolonged exposure to indoor pollutants such as biomass fuels and tobacco smoke are particularly vulnerable.^[15-17] These socioeconomic and environmental determinants not only increase the incidence of LRTIs but also make adverse consequences more likely.^[8] HIV-related immunodeficiency, prevalent in many LMICs, further compounds these risks and is also underrepresented in literature.^[18]

HOSPITALIZATION AND AGE AS RISK FACTORS

Children requiring inpatient care face a much higher likelihood of developing chronic complications than those managed outside hospital settings.^[4,13,14,16] Hospitalization often reflects greater disease severity, and longitudinal studies have shown that these children are more likely to experience persistent wheezing, reduced lung function, and long-term respiratory morbidity.^[13] Early life hospitalization for pneumonia, particularly in the first 3 years, has been linked to altered lung growth trajectories and increased risk of asthma and COPD in adulthood.^[14]

COMPLICATIONS OF BACTERIAL PNEUMONIA

Bacterial pneumonia in children can lead to severe acute complications, including pneumatoceles, necrotizing pneumonia, empyema, and lung abscesses, all of which may prolong recovery and increase morbidity.^[3,19,20] Pneumatoceles are air-filled cystic lesions that typically arise from Staphylococcus aureus or S. pneumoniae infections. They result from alveolar wall necrosis and inflammation. While many resolve spontaneously, large or infected pneumatoceles may require drainage or surgical intervention. Occasionally, a lung abscess may arise within a congenital thoracic malformation [Figure 1], necessitating surgical resection to prevent recurrence.^[3,20] Necrotizing pneumonia is characterized by extensive lung tissue destruction and cavitation. Although radiologically dramatic, most children recover well with appropriate antibiotic therapy and supportive care.^[17] Management may be complicated by coexisting pleural disease, including empyema, which often requires imaging-guided drainage or surgical decortication.^[20] Despite the severity of these complications, long-term outcomes are generally favorable when managed promptly. Studies show that children who survive necrotizing pneumonia often regain normal lung function over time.^[19,20]

Close

Figure 1:

Congenital thoracic malformation with lung abscess. Chest X-ray shows localized opacity and cystic changes suggestive of congenital malformation. Blue arrow indicates localized opacity and cystic changes.

Export to PPT

COMPLICATIONS OF M. PNEUMONIAE

M. pneumoniae is notable for its diverse respiratory complications in children. Airway-related outcomes include bronchiolitis obliterans (BO), asthma-like syndromes, and persistent cough.^[7,21] A “treatable-traits” approach is increasingly emphasized, aligning with current airway disease management guidelines.^[22,23] Although macrolide resistance is rising, it does not appear to increase the risk of BO.^[7] Prolonged azithromycin use has shown empirical benefit in some settings, though randomized trial data remain limited.^[7]

The existence of cough variant asthma (CVA) as a distinct entity post-Mycoplasma infection is debated. However, the pathogen is consistently associated with prolonged cough and airway hyperresponsiveness.^[7,22] A meta-analysis found elevated immunoglobulin E and eosinophil levels in CVA patients, along with higher Mycoplasma immunoglobulin M positivity.^[7]

Extrapulmonary manifestations such as encephalitis and mucositis are documented but fall outside the scope of this respiratory-focused review. These complications are summarized in Table 1.

COMPLICATIONS OF VIRAL PNEUMONIA

Viral pneumonia can result in long-term respiratory consequences, including BO [Figure 2], bronchiectasis [Figure 3], MacLeod syndrome [Figure 4], and adult-onset COPD.^[21,24-26] BO causes permanent narrowing of the small airways due to inflammation and scarring. MacLeod syndrome (also called Swyer–James–MacLeod syndrome) is a rare, post-infectious lung disorder characterized by a unilateral hyperlucent lung, usually due to obliterative bronchiolitis in childhood. Post-adenovirus BO (PIBO) is especially common in LMICs, with risk factors including severe initial infection, prolonged hospitalization, and underlying immunodeficiency.^[21,24] Chronic lung dysfunction such as bronchiectasis, PIBO, and MacLeod syndrome may be progressive or fixed, depending on etiology and stem from early viral pneumonia and have no current treatment.^[21,24] Bronchiectasis often worsens over time through infection-driven inflammation, airway remodeling, and fibrosis.^[25,26]

Close

Figure 2:

Post-infectious bronchiolitis obliterans. Cross-sectional computed tomography scan showing bilateral areas of air trapping and structural distortion. The image highlights mosaic perfusion and large airway involvement, consistent with post-infectious bronchiolitis obliterans. Blue arrow indicates mosaic perfusion pattern on chest CT.

Export to PPT

Close

Figure 3:

Bronchiectasis showing airway dilation and wall thickening. Computed tomography scan revealing dilated bronchi with thickened walls, characteristic of bronchiectasis. The image highlights chronic airway inflammation and remodeling. Blue arrow indicates dilated bronchi with thickened walls.

Export to PPT

Close

Figure 4:

MacLeod syndrome with unilateral hyperlucency. Coronal computed tomography scan showing unilateral hyperlucency of the right lung, consistent with MacLeod syndrome. The left lung shows increased opacity, while the right lung appears over-aerated with reduced vascular markings. Blue arrow indicates unilateral hyperlucency of the right lung.

Export to PPT

RSV is the predominant viral pathogen in infants, primarily associated with wheezing and asthma development,^[6,14] while the influenza virus more often leads to severe systemic illness, including acute respiratory distress syndrome and multi-organ complications.^[27] A study of hospitalized influenza patients (2012–2016) showed that pre-existing heart disease, confusion at admission, and pneumonia severity predicted complications, while high C-reactive protein and low oxygen saturation correlated with poor outcomes.^[27] Risk for a more virulent adenovirus-associated PIBO increases with severe initial illness, prolonged fever, and coinfections.^[21] Chest computed tomography radiological findings in PIBO include patchy air trapping and large airway involvement [Figure 2]. Follow-up spirometry often shows impairment, as do impulse oscillometry and multiple breath washout. African experiences were recently reviewed, and among over 200 cases, 14.1% developed CLD, many with hypoxemia at presentation. HIV affected about 7%, and nearly 9% died.^[28] Airway dilation and fibrosis are usually irreversible.^[29] No evidence-based treatments exist, but pulsed steroids and azithromycin have been tried empirically.^[21,24,29]

Persistent post-viral cough is a lingering irritative cough that often remains due to heightened airway sensitivity, sometimes lasting weeks or months after the infection clears.

It is thought to be due to mucosal damage and neurogenic inflammation, making the airways hypersensitive to environmental triggers, but in most cases, definitive evidence is lacking. This must be distinguished from “cough variant asthma” as discussed earlier.^[22]

LONG-TERM PULMONARY EFFECTS OF COVID-19

COVID-19 pneumonia presents unique challenges in pediatric populations. While adult survivors generally show good recovery, emerging pediatric data reveal cases of BO and CLD following SARS-CoV-2 infection.^[30,31] Persistent structural damage, including pulmonary fibrosis and airway remodeling, has been observed in some children, and restrictive lung patterns with reduced diffusion capacity have been documented in follow-up studies.^[32] Early reports also suggest vascular injury and microthrombi may contribute to lasting dysfunction.^[33] Although adult studies provide insight into fibrotic changes and imaging abnormalities, their relevance to children is uncertain due to differences in immune response and lung plasticity.^[30,33] Pediatric-focused research is urgently needed to clarify the trajectory of post-COVID lung recovery in early life.

MATERNAL INFECTIONS AND PREGNANCY

Maternal infections during pregnancy, including CMV, HIV, rubella, syphilis, and SARS-CoV-2, can disrupt immune programming and alveolarization. These intrauterine exposures impair lung development and predispose infants to chronic respiratory morbidity.^[34,35] Evidence from the Drakenstein cohort has demonstrated that maternal HIV and CMV exposure are associated with impaired infant lung function trajectories, underscoring the long-term impact of maternal health on pediatric respiratory outcomes.^[8,14] Studies have also shown that maternal RSV infection can lead to vertical transmission and altered cytokine profiles in neonates, potentially predisposing them to wheezing and asthma.^[36] In addition, maternal inflammation and fever during pregnancy have been associated with increased risk of childhood asthma and impaired lung function.^[37]

Maternal vaccination, however, protects mothers and infants by reducing infection risk and transferring antibodies, with established vaccines (influenza, pertussis, rubella, SARS-CoV-2) and emerging RSV strategies showing promise.^[38]

INVESTIGATING LRTI SEQUELAE IN CHILDREN

All children with LRTI require thorough history-taking and physical examination. Any unexpected findings should prompt further testing, particularly in cases of recurrent pneumonia.^[39] There is no internationally agreed consensus on how many recurrent infections are considered normal. Delphi proposals, largely derived from high-income countries, include combinations of respiratory tract infection and pneumonia, which appear broad compared with other suggestions.^[40]

True recurrent pneumonia must be distinguished from a frequent wet cough due to viral infections. When symptoms such as crackles, clubbing, or hypoxemia are present alongside abnormal imaging, childhood interstitial lung disease (chILD), should be considered.^[41]

Diagnosis is suggested when at least four features are present together. These include the presence of respiratory symptoms such as cough, rapid breathing, or exercise intolerance, combined with clinical chest signs like crackles, clubbing, or intercostal retractions. In addition, hypoxemia accompanied by chest X-ray abnormalities strengthens the suspicion. When these elements coexist, they provide sufficient evidence to support a diagnosis.

Repeated imaging is rarely necessary for uncomplicated pediatric pneumonia. A single chest X-ray usually suffices, with follow-up imaging considered only if symptoms persist, complications arise, pneumonia recurs, or initial findings suggest atypical pathology.^[42] High-risk children, such as those with immune deficiencies, may require closer monitoring.^[43] Routine follow-up imaging is unnecessary unless atypical features such as round pneumonia, atelectasis, or unresolved symptoms are present. Parents should be counseled that if the cough persists, they should return for evaluation.^[44] Studies from high-income settings show limited benefit from routine follow-up radiographs. However, in populations with elevated risk or recurrent disease, selective imaging may be warranted. Decisions should balance radiation exposure, cost, and regional disease patterns.^[45]

ADULT OUTCOMES FOLLOWING EARLY-LIFE -LRTIS

Longitudinal studies have shown that early-life LRTIs are associated with increased risk of chronic respiratory conditions in adulthood, including asthma, COPD, and reduced lung function.^[46] The Tucson Children’s Respiratory Study demonstrated that infants with RSV bronchiolitis had higher rates of wheezing and asthma into adolescence and early adulthood.^[47] Similarly, the Perth cohort revealed that children hospitalized for pneumonia before the age of 3 years had lower forced expiratory volume in the first second and forced vital capacity values as adults, suggesting long-term impairment.^[48] These findings were independent of smoking status and socioeconomic background. In LMICs, the Drakenstein cohort showed that early LRTIs were linked to persistent lung function deficits at school age, with implications for adult respiratory health.^[49] Mechanistically, early inflammation may disrupt alveolar development and immune regulation, leading to airway remodeling and reduced reserve capacity.^[50] These changes may not manifest until adulthood, especially under stressors such as pollution or smoking.

Thus, early LRTIs serve as a marker for future respiratory vulnerability, and long-term follow-up is essential to mitigate adult disease burden.^[51]

FUTURE RESEARCH PRIORITIES

Future work should clarify mechanisms linking viral injury and immune dysregulation to long-term lung sequelae. Large pediatric cohorts in LMICs are needed to capture infection–environment–socioeconomic interactions across lung development. Standardized definitions of recurrent pneumonia and post-infectious complications will improve comparability. Evaluating RSV prophylaxis in high-risk groups, validating immunodeficiency screening tools for resource-limited settings, [Table 2], and developing cost-effective imaging protocols are key priorities to guide prevention and monitoring strategies.^[52,53]

CONCLUSION

Early childhood LRTIs cause lasting harm, predisposing survivors to asthma, COPD, and reduced lung function. Prevention through immunization, improved nutrition, reduced pollution, and long-term monitoring is vital, supported by a strong public health commitment.