Influenza A virus infection in infants.

Influenza A virus causes a variety of respiratory and nonrespiratory illness in children. The symptomatology varies with different age groups. The purpose of this retrospective study was to define the clinical characteristics of influenza A infection in Taiwanese infants. During the period from December 1997 to February 1998, 37 febrile patients younger than 1 year of age, including five newborns, were admitted to our hospital due to suspicion of sepsis or meningitis. The medical records of these patients were retrospectively evaluated. Influenza A virus was isolated from the specimens of the throat swabs in all patients, whereas no bacterial pathogen was detected. The most common clinical manifestations of these infants were lower respiratory tract infections, including pneumonia, bronchiolitis, and croup. There was no significant difference between the clinical characteristics of infants younger than 3 months and those aged from 3 months to 1 year. The mean duration of fever, peak of body temperature, and duration of hospitalization were 3.41 (+/-1.86) versus 4.4 (+/-2.02) days, 39.0 (+/-0.57) versus 39.9 (+/-0.63) oC, 4.9(+/-1.49) versus 6.3 (+/-3.7) days in infants younger than 3 months and infants aged from 3 months to 1 year, respectively. The older infants aged from 3 months to 1 year had a significantly higher peak body temperature than the infants younger than 3 months (p < 0.05). Two patients with croup had a more severe clinical course, however, the outcomes were good in all patients. During an influenza A virus outbreak, influenza A infection should be included in the differential diagnosis of infants with lower respiratory tract infection.