The course of fever following influenza virus infection in children treated with oseltamivir.

Although the effectiveness of oseltamivir against influenza virus infection is well known, there has been no report analyzing the detailed time course of fever following the drug treatment in children. Oseltamivir was prescribed for 4 days to every child with a positive result for rapid immunological test for influenza virus during 2002--2003, 2003--2004, and 2004--2005 epidemics. Only those who were 1-12 years of age and prescribed oseltamivir within 24 hr after the onset of fever were included in the analysis. The numbers of children with type A/H3N2 disease for the three seasons were 64, 77, and 33, and those with type B disease were 102, 4, and 86, for the respective seasons. The period until normalization of temperature was obtained from six-hourly recordings of body temperature. By multiple regression analysis, temperature periods were longer in type B than in type A/H3N2 disease, negatively associated with age, and positively with maximal body temperature (all: P < 0.001). The effectiveness of oseltamivir on body temperature in type B disease was less apparent in the 2004--2005 than in the 2002--2003 season, irrespective of age. No such between-season difference was observed for Type A/H3N2 disease. Frequencies of ineffective cases with biphasic fever (19.6% and 43.0% during 2002--2003 and 2004--2005 seasons) were significantly higher in type B than in type A/H3N disease (12.0% and 11.8%, respectively). The effectiveness of oseltamivir depends on a child's age, maximal body temperature and the virus type. This study confirmed recent reports indicating decreased effectiveness of oseltamivir against type B disease.