Clinical characteristics of children hospitalized for influenza virus infection

Background: The clinical manifestations of influenza virus are fairly nonspecific and are similar to those of other viral infections, respiratory processes due to other causes and even septic disease in neonates. Few studies have been performed of the clinical characteristics of influenza virus infection in hospitalized children.

Objective: To evaluate the clinical characteristics of children hospitalized for influenza virus infection in four consecutive epidemic waves (2000-2004).

Methods: We retrospectively reviewed the medical records of children hospitalized for influenza A and B virus infection confirmed by cell culture and polymerase chain reaction. Age, sex, symptoms on admission, complementary investigations, diagnosis and outcome were evaluated.

Results: Eighty-four children were hospitalized, of which 74 had influenza virus type AH3, five had influenza virus type AH1 and five had influenza B virus. A total of 42.8 % were aged less than 6 months. The main symptoms were fever (75 patients), cough (56 patients) and ENT involvement (53 patients). The most frequent causes of admission were febrile syndrome (75 patients), bronchiolitis (19 patients), pneumonia (13 patients) and bronchitis (8 patients). In 21 patients viral or bacterial coinfection was found, the most frequent of which was respiratory syncytial virus (10 patients). Few differences were found among age groups except for pneumonia and prolonged fever (more frequent in children older than 6 months) and lymphocytosis (in children younger than 6 months). The greatest number of complementary investigations in younger children was performed for acute febrile syndrome in neonates aged less than 6 months. Risk factors for hospitalization were found in only three children, all of whom were older than 6 months. Outcome was favorable in all children.

Conclusions: Influenza virus infection in hospitalized children is most frequent in previously healthy neonates with fever and nonspecific signs and symptoms that are similar to those of other infectious processes. Specific microbiological diagnostic techniques are required for an early diagnosis. Healthy infants aged less than 24 months are most at risk for hospitalization for influenza virus infection.