The effects of influenza virus infection on FEV1 in asthmatic children. The time-course study

To study the time-course of influenza-induced asthma, we retrospectively examined FEV1 from five days before to ten days after the onset of illness in 20 asthmatic children aged 8 to 12 years with tolerable respiratory symptoms. Influenza infection was confirmed by a rise at least fourfold in serum complement fixation titers. Fifteen of 20 patients had decrease in FEV1 more than 20 percent from baseline during the acute stage. FEV1 began to decrease with the onset of illness in the 15 patients with the exception of one whose FEV1 decreased during the incubation period. It continuously decreased on the second day, when mean (+/- SD) decrease in FEV1 became maximum, 30.3 +/- 10.9 percent. It began to improve on the third day, and returned within 10 percent difference on the seventh to tenth day. We conclude that influenza-induced asthma may continuously deteriorate during the first two days of illness and may require at least seven days for recovery.