Epidemiological and clinical profile between influenza A and B virus in Costa Rican children.

Objective: We aimed to evaluate the clinical and epidemiological behavior of influenza type A versus type B and analyze if there was any correlation or differences between the characteristics of both groups.

Methods: An observational, retrospective, descriptive, and population-based study based of children who were hospitalized at the only national pediatric hospital of Costa Rica from January 1, 2010 to December 31, 2018 and had a confirmed influenza virus infection.

Results: 336 patients were analyzed. Mean age was 35,6 ± 36,7 months (3,0 ± 3,1 years). The only significant variables at 25% in relation to influenza type A or B virus were: sex, month of diagnosis, fever, vomiting, cough, use of antibiotics and admission to the PICU. The hospitalization rate at our hospital increased between the months of October to December, with a higher percentage of cases in November and December, which reveals that the "real peak" in our population begins between 3 to 4 months after the end of the vaccination campaign. Patients with influenza A virus had a 2.5 times greater risk of being admitted to the PICU. Mortality rate was 0.6% and 0% among influenza A and B children, respectively.

Conclusions: Variables in which a causality was found with type A or B virus were: admission to the PICU, month of diagnosis, and cough. However, influenza B clinical behavior continues to be unpredictable.