To evaluate the rate of hospitalization for acute respiratory tract infection in children less than 24 months with haemodynamically significant congenital cardiac disease, and to describe associated risk factors, preventive measures, aetiology, and clinical course.

We followed 760 subjects from October 2004 through April 2005 in an epidemiological, multicentric, observational, follow-up, prospective study involving 53 Spanish hospitals.

Of our cohort, 79 patients (10.4%, 95% CI: 8.2%–12.6%) required a total of 105 admissions to hospital related to respiratory infections. The incidence rate was 21.4 new admissions per 1000 patients-months. Significant associated risk factors for hospitalization included, with odds ratios and 95% confidence intervals shown in parentheses: 22q11 deletion (8.2, 2.5–26.3), weight below the 10th centile (5.2, 1.6–17.4), previous respiratory disease (4.5, 2.3–8.6), incomplete immunoprophylaxis against respiratory syncytial virus (2.2, 1.2–3.9), trisomy 21 (2.1, 1.1–4.2), cardiopulmonary bypass (2.0, 1.1–3.4), and siblings aged less than 11 years old (1.7, 1.1–2.9). Bronchiolitis (51.4%), upper respiratory tract infections (25.7%), and pneumonia (20%) were the main diagnoses. An infectious agent was found in 37 cases (35.2%): respiratory syncytial virus in 25, Streptococcus pneumoniae in 5, and Haemophilus influenzae in 4. The odds ratio for hospitalization due to infection by the respiratory syncytial virus increases by 3.05 (95% CI: 2.14 to 4.35) in patients with incomplete prophylaxis. The median length of hospitalization was 7 days. In 18 patients (17.1%), the clinical course of respiratory infection was complicated and 2 died.

Hospital admissions for respiratory infection in young children with haemodynamically significant congenital cardiac disease are mainly associated with non-cardiac conditions, which may be genetic, malnutrition, or respiratory, and to cardiopulmonary bypass. Respiratory syncytial virus was the most commonly identified infectious agent. Incomplete immunoprophylaxis against the virus increased the risk of hospitalization.