Acute respiratory infections remain one of the most formidable challenges in global child health, and a new ecological study from Colombia now offers one of the most detailed pictures yet of how these illnesses behave in a major Latin American setting. Drawing on extensive national health system databases, researchers led by Natalia Sanabria-Herrera of Clínica Universidad de la Sabana traced the burden of severe acute respiratory infections among children under five years old across five of Colombia’s largest cities throughout 2018. Their findings, published in BMC Pediatrics, quantify for the first time at this scale how often these infections send young children to emergency departments, hospital wards, and intensive care units, and which pathogens and diagnoses carry the greatest lethal risk.

The scale of the problem is striking. After adjusting for age and sex, the researchers calculated an incidence rate of 3,488 cases per 10,000 children per year across the five selected cities. In practical terms, that means roughly one in every three children under five in these urban populations required emergency care, hospitalization, or intensive care for an acute respiratory infection within a single year. The figure underscores how ubiquitous these infections are in early childhood, a period when immature airways, developing immune systems, and frequent exposure to circulating viruses converge to make respiratory illness the leading reason for pediatric medical attention worldwide.

The study was designed as a descriptive, ecological analysis covering the full calendar year from January 1 to December 31, 2018. The team mined administrative records from Colombia’s national health system, including the Integrated Social Protection Information System known as SISPRO, to identify every case of acute respiratory infection that resulted in emergency department attendance, hospital admission, or intensive care unit admission. Cases were classified using the International Classification of Diseases, 10th Revision, alongside Colombia’s own Unified Medicine Coding and Common Unified Procedure Coding System, allowing the researchers to link clinical diagnoses, levels of care, and mortality outcomes across the entire care pathway. Because the analysis relied on fully anonymized administrative data rather than direct patient contact, the Medical Ethics Committee at Universidad de La Sabana granted approval without requiring individual informed consent, in line with Colombian biomedical research law and the Declaration of Helsinki.

The median age of children in the studied sample was two years, but age proved to be a decisive factor in how severe the disease became. Children who required intensive care were significantly younger than those who did not, with a median age of just one year in the ICU group compared with two years in the non-ICU group, a difference that was highly statistically significant. This gradient of vulnerability with decreasing age is a recurring theme in pediatric respiratory medicine, and the Colombian data confirm it with unusual clarity because of the sheer size of the population examined. The youngest infants, whose small airways are most easily obstructed by inflammation and whose immune defenses are least experienced, consistently occupied the most severe end of the disease spectrum.

When the researchers examined which diagnoses dominated, bacterial pneumonia emerged as the single most common clinical diagnosis across the cohort. Among viral causes, respiratory syncytial virus, or RSV, stood out as the leading etiological agent, and its dominance was particularly pronounced among children admitted to intensive care. RSV is well known to pediatricians as the classic cause of bronchiolitis, an infection that clogs the tiny bronchioles of infants with mucus and cellular debris, and the Colombian findings align with decades of international evidence placing RSV at the center of severe infant respiratory disease. The convergence of high bacterial pneumonia incidence and heavy RSV circulation in the same population highlights a dual burden: a virus that fills pediatric intensive care units and a bacterial pathology that generates the largest overall volume of serious cases.

Mortality in the cohort was low in absolute terms but sharply patterned by age and diagnosis. The highest death rate was observed in children under one year of age, at 0.2 percent, a figure that was statistically significant. Within that group, bronchiolitis carried the highest case fatality at 0.3 percent, followed by bacterial pneumonia at 0.1 percent, both reaching statistical significance. Among children who reached the intensive care unit, mortality rose to 0.8 percent, again a significant finding. Notably, although RSV was the most common viral etiology overall and dominated ICU admissions, only a single death in the dataset was attributed to the virus, suggesting that with adequate supportive care, including the oxygen therapy and mechanical ventilation available in Colombian pediatric intensive care, most children infected even with the most dangerous respiratory virus can survive.

Seasonality emerged as another defining feature of the epidemic landscape. The study found that incidence peaks aligned with Colombia’s rainy season, a pattern the authors link to climatic conditions documented by the Institute of Hydrology and Environmental Studies, known by its Spanish acronym IDEAM. In tropical countries, respiratory virus transmission does not follow the winter rhythm familiar from temperate latitudes; instead, increases in rainfall and humidity create conditions favorable to viral survival and transmission, while keeping children crowded indoors. For health system planners, this seasonal signature is invaluable: it defines predictable windows when emergency services, hospital beds, and pediatric intensive care capacity come under maximum pressure, and when preventive measures such as RSV immunization campaigns would deliver the greatest benefit if timed appropriately.

The methodological strength of the work lies in its comprehensiveness. Rather than relying on sentinel sites or voluntary reporting, which can distort the apparent burden of disease, the researchers harnessed the administrative infrastructure of Colombia’s universal health system, in which Healthcare Insurers, or EPS, register affiliations through the Unique Registry of Affiliates and procedures are coded through standardized national systems. This allowed the team to assemble a near-complete picture of severe respiratory disease across five major cities simultaneously. The trade-off inherent in ecological and administrative designs is that coding accuracy depends on clinical documentation, and the study cannot establish individual-level causal relationships between exposures and outcomes. Nevertheless, for measuring the magnitude and distribution of a disease burden, population-scale administrative data of this kind are among the most powerful tools available to epidemiologists.

The findings arrive at a moment of rapid change in the global response to pediatric respiratory disease. RSV prevention has been transformed in recent years by the approval of long-acting monoclonal antibodies for infants and of maternal vaccines, giving countries for the first time practical tools to blunt the annual RSV surge. The Colombian data provide exactly the kind of local evidence that national authorities need to decide how and when to deploy such interventions: they identify infants under one year, and especially those with bronchiolitis, as the group at highest risk of death, and they pinpoint the rainy season as the period of peak transmission. The authors argue that targeted interventions, improved surveillance, and healthcare strategies tailored to the country’s specific epidemiology are essential to reducing the impact of these infections on the most vulnerable children.

Beyond its immediate policy implications, the study fills an important gap in the scientific literature. The authors note that clinical data on viral etiology and outcomes in Latin America have been scarce, leaving the region underrepresented in the global estimates produced by initiatives such as the Global Burden of Disease project and the World Health Organization’s respiratory illness surveillance. By documenting an adjusted incidence approaching 3,500 severe cases per 10,000 children per year, a clear age gradient in severity, a dominant viral pathogen, and a mortality profile concentrated in the first year of life, the Colombian team has supplied a benchmark against which other countries in the region can now measure themselves. As RSV immunization programs roll out across Latin America in the coming years, studies of this kind will serve as the baseline that determines whether those investments are actually reducing the toll of severe respiratory disease on the region’s youngest children.

Subject of Research: Epidemiology of severe acute respiratory infections in children under five in Colombia

Article Title: Patterns of severe acute respiratory infections in children under five years old in Colombia: an ecological study

Article References: Sanabria-Herrera, N., Agudelo, S., Gutiérrez, J. D., Gutiérrez, V. A., & Oliveros, H. (2026). Patterns of severe acute respiratory infections in children under five years old in Colombia: an ecological study. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07576-x

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07576-x

Keywords: acute respiratory infections, Colombia, children under five, RSV, bacterial pneumonia, bronchiolitis, pediatric epidemiology, intensive care, seasonality, surveillance, public health, Latin America

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Tags: acute respiratory infectionsbacterial pneumoniabronchiolitischild mortality due to respiratory infectionschildhood respiratory illness epidemiologychildren under fiveColombiaColombia child health dataepidemiological study of respiratory infections in Latin Americahealth system burden of pediatric respiratory diseaseshospitalization rates for respiratory infectionsintensive careLatin Americapathogens causing childhood respiratory illnesspediatric epidemiologypediatric respiratory infectionsPublic healthpublic health strategies for childhood respiratory illnessesrisk factors for severe respiratory infections in childrenRSVseasonalitysevere acute respiratory infections in childrensurveillanceurban pediatric respiratory disease