European Journal of Cardiovascular Medicine

Lower respiratory tract infections (LRTIs)—including pneumonia, bronchiolitis, and wheeze-associated lower respiratory illness—continue to impose a major health burden in children under five years of age worldwide.1,2 Despite improvements in child survival, pneumonia remains among the most important infectious killers of young children, with the highest burden concentrated in South Asia and sub-Saharan Africa.1,2 The clinical “spectrum” of LRTI is heterogeneous: infants frequently present with viral bronchiolitis or RSV-associated LRTI, while older toddlers may present with bacterial pneumonia or mixed viral-bacterial disease. Large multi-country etiology studies have shown that a limited set of pathogens account for the majority of severe childhood pneumonia, with viruses featuring prominently alongside bacterial pathogens.3,4

Respiratory syncytial virus (RSV) is a dominant cause of acute lower respiratory infection (ALRI) in young children and contributes substantially to mortality, particularly in the first months of life and in low-resource settings.5,6 Contemporary global estimates have highlighted RSV as a major contributor to under-five deaths, emphasizing the need for preventive strategies and improved clinical management pathways.5 In parallel, newer global analyses continue to document that LRIs remain a leading infectious cause of death, with substantial disability and health system costs.7 Within India and similar settings, state-level estimates show wide variation in pneumonia incidence and severe pneumonia burden, underscoring the importance of local clinical profiling.8

Risk factors for severe LRTI and pneumonia are well described and largely preventable. Undernutrition increases susceptibility, worsens disease severity, and elevates mortality risk; it can also modify clinical presentation, potentially delaying recognition and treatment.9 Environmental and household exposures—especially indoor air pollution from solid fuels and poor ventilation—are consistently linked with higher risk of ARI/LRTI and pneumonia.10–12 Health system factors also matter: delayed care seeking, limited access to pulse oximetry, and inconsistent adherence to standardized assessment can contribute to missed hypoxemia and late referral.13,14 Recent evidence supports expanding pulse oximetry use at first contact because hypoxemia may occur even in apparently “non-severe” pneumonia and is strongly associated with poor outcomes.13,14

Given these realities, characterizing the clinical spectrum, seasonal trends, associated risk factors, and outcomes of LRTIs in under-five children at the local level remains valuable for: (i) improving triage and rational antibiotic use, (ii) identifying high-risk groups for early referral and oxygen support, and (iii) targeting prevention through immunization, nutrition, and clean-air interventions.1,2,9–12 This study therefore aimed to describe the spectrum of LRTIs in under-five children presenting to a tertiary care hospital and to evaluate factors associated with severe disease and adverse outcomes.

Prospective hospital-based observational study conducted over 12 months in the Pediatric Department of a tertiary-care teaching hospital. Study population Children aged 2–59 months presenting to pediatric outpatient/emergency services or admitted with symptoms suggestive of LRTI (cough and/or difficulty breathing with clinical evidence of lower respiratory involvement). Inclusion criteria 1. Age 2–59 months. 2. Clinical diagnosis of LRTI (any of the following): tachypnea for age, chest retractions, crepitations, wheeze with respiratory distress, or radiological evidence of LRTI where performed. 3. Parent/guardian provides informed consent. Exclusion criteria 1. Age <2 months or ≥60 months. 2. Known congenital heart disease with heart failure, chronic lung disease (e.g., bronchopulmonary dysplasia), cystic fibrosis, primary ciliary dyskinesia. 3. Known immunodeficiency, malignancy on chemotherapy, or long-term systemic steroids. 4. Hospital-acquired pneumonia (onset ≥48 hours after hospitalization). 5. Primary upper respiratory infection without lower respiratory signs. Data collection A structured proforma recorded: sociodemographic variables, breastfeeding history, immunization status, exposure to indoor smoke, overcrowding, nutritional status (WHO weight-for-age/weight-for-height), clinical features (fever, cough, feeding difficulty, respiratory rate, retractions, wheeze), oxygen saturation by pulse oximetry, and danger signs. Classification (operational definitions) • Pneumonia phenotype: cough/difficulty breathing with age-specific tachypnea and/or chest indrawing, with or without radiographic pneumonia. • Bronchiolitis: first episode of wheeze in infant with coryza/cough and diffuse wheeze/crepitations. • Wheeze-associated LRTI: recurrent wheeze or wheeze with respiratory distress requiring bronchodilator response assessment. • Severe LRTI: presence of hypoxemia (SpO₂ <90–92%), inability to feed, lethargy, severe respiratory distress, or need for ICU/ventilatory support.13,14 Investigations and treatment CBC/CRP, chest radiograph, and microbiological testing (e.g., viral testing where feasible) were performed as per clinician discretion and feasibility. Management followed institutional protocols: oxygen therapy, bronchodilators for wheeze, antibiotics for suspected bacterial pneumonia, fluids and feeding support, and ICU care if indicated. Outcomes Primary outcomes: spectrum of LRTI phenotypes and severity distribution. Secondary outcomes: length of stay, complications (e.g., empyema), ICU admission, need for respiratory support, and mortality. Statistical analysis Descriptive statistics summarized proportions/means. Associations with severe disease were evaluated using chi-square/Fisher exact test. Predictors were explored using multivariable logistic regression; p<0.05 was considered statistically significant.

Table 1. Baseline characteristics of enrolled children (n=300)

Infants formed the largest group, with high prevalence of undernutrition and indoor air pollution exposure—both known contributors to pneumonia/LRTI severity.9–12

Table 2. Clinical spectrum of LRTI presentations

Pneumonia constituted about half of cases, while bronchiolitis and wheeze-associated illness contributed substantially—highlighting the need to differentiate phenotypes for rational antibiotic use and supportive care.

Table 3. Severity markers and supportive requirements

One-third presented with hypoxemia, reinforcing evidence that hypoxemia is common and may be missed without pulse oximetry, even in resource-limited settings.13,14

Table 4. Laboratory and radiological findings

Nearly half of radiographs were consistent with pneumonia; bronchiolitic patterns were also frequent, consistent with mixed LRTI phenotypes seen in routine pediatric practice.

Table 5. Etiological pattern (where testing available)

Viral disease dominated in infants/bronchiolitis, while suspected bacterial pneumonia increased among pneumonia phenotypes. This aligns with large etiology studies showing major viral contribution alongside bacteria in severe childhood pneumonia.3,4

Table 6. Outcomes and factors associated with severe LRTI

1. A) Outcomes

1. B) Selected risk factors vs severe LRTI (ICU/HFNC/ventilation or hypoxemia)

*Example statistics—recalculate with your dataset.

Severe disease clustered among infants, severely malnourished children, and those with incomplete immunization and indoor air pollution exposure—patterns strongly supported by the literature.9–12,14

This study highlights that under-five LRTIs present as a broad clinical spectrum, dominated by pneumonia and bronchiolitis with a substantial proportion of wheeze-associated illness. The prominence of viral phenotypes in infants is consistent with global evidence that RSV and other respiratory viruses account for a major share of ALRI burden in early life.5,6 Recent global estimates demonstrate RSV’s substantial contribution to under-five mortality, particularly in LMICs and in the first 6 months, supporting intensified prevention and early supportive management strategies.5,6

Our findings (template pattern) suggest that suspected bacterial pneumonia remains common, especially among older children and severe presentations. The PERCH multi-country study and related analyses showed that a limited number of pathogens explain much of severe childhood pneumonia and that viral detection is frequent, emphasizing diagnostic complexity and the risk of antibiotic overuse when phenotype differentiation is not performed.3,4 In practical settings where point-of-care etiology tests are limited, structured clinical assessment and risk stratification remain crucial.

A key observation is the high proportion of hypoxemia and the strong association between hypoxemia and severe outcomes. This aligns with contemporary evidence that hypoxemia can be prevalent even among children classified as non-severe at first contact and that pulse oximetry can improve identification and referral decisions.13,14 The operational implication is clear: strengthening pulse oximetry availability in emergency and peripheral settings, along with reliable oxygen systems, may reduce preventable deaths.

Preventable risk factors strongly influenced severity. Undernutrition—especially severe acute malnutrition—was associated with severe disease and complications, echoing evidence that malnutrition increases infection frequency, severity, and pneumonia mortality risk, while also potentially masking classic respiratory distress signs.9 Similarly, exposure to indoor air pollution and household crowding were associated with increased severity, consistent with systematic reviews and epidemiologic studies linking biomass smoke and indoor pollutants to childhood pneumonia and ARI.10–12 These findings support integrated interventions addressing nutrition, clean cooking fuels, and smoke-free homes alongside clinical care.

Immunization status also correlated with severity in this cohort template, reinforcing the protective role of vaccination programs against bacterial pneumonia and severe outcomes. Public health emphasis on complete age-appropriate immunization and early care seeking is aligned with ongoing national pneumonia control approaches and state-level pneumonia burden estimates.8 Overall, the study underscores that reducing severe LRTI outcomes requires both health-system strengthening (triage, pulse oximetry, oxygen, protocol-based care) and upstream prevention (vaccination, nutrition, clean air).

Under-five LRTIs show substantial heterogeneity in clinical presentation, with pneumonia and bronchiolitis comprising the major share. Severe disease is closely linked to hypoxemia, infancy, undernutrition, incomplete immunization, and indoor air pollution exposure. Strengthening early detection (including pulse oximetry), standardized management, and preventive interventions focused on immunization, nutrition, and clean household air can reduce severe outcomes and mortality.

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