Effects of viral lower respiratory tract infection on lung function in infants with cystic fibrosis

Objective. To determine the effect of respiratory viral infections on pulmo nary function in infants with cystic fibrosis (CF) after the respiratory vi rus season (October through March). Methods. Recruitment was for one respiratory virus season during a 3-year s pan, 1988 to 1991, with reenrollment allowed; 22 infants <2 years of age wi th CF (30 patient-seasons) and 27 age-matched controls (28 patient-seasons) participated. Primary outcome variables were preseason and postseason pulm onary function tests and serology for viral antibodies. Twice-weekly teleph one calls screened for respiratory symptoms. The presence of respiratory sy mptoms triggered a home visit and an evaluation for upper or lower (LRTI) r espiratory tract infection. A nasopharyngeal sample for viral culture was p erformed with each visit. Results. Controls and CF infants each had a mean of 5.3 acute respiratory i llnesses; CF infants were four times more likely to develop an LRTI compare d with controls (odds ratio, 4.6; 95% confidence interval, 1.3 and 16.5). T hree of 7 (43%) CF infants with respiratory syncytial virus infection (docu mented by culture) required hospitalization. Controls had no association be tween respiratory illness and postseason pulmonary function. For CF infants , reduced postseason maximal flow at functional residual capacity (V'(max)- FRC) was associated with two interactions, ie, respiratory syncytial virus infection and LRTI, and male sex and LRTI; increased gas trapping (FRC) wa s associated with an interaction between respiratory syncytial virus and LR TI and day care. Postseason pulmonary function tests were obtained a mean o f 3.2 months after final LRTI. Conclusions. Infants with CF incurring respiratory virus infection are at s ignificant risk for LRTI, for hospitalization, and for deterioration in lun g function that persists months after the acute illness.