PICNIC (PEDIATRIC INVESTIGATORS COLLABORATIVE NETWORK ON INFECTIONS IN CANADA) STUDY OF THE ROLE OF AGE AND RESPIRATORY SYNCYTIAL VIRUS NEUTRALIZING ANTIBODY ON RESPIRATORY SYNCYTIAL VIRUS ILLNESS IN PATIENTS WITH UNDERLYING HEART OR LUNG-DISEASE

Objective. To determine the effects of age and respiratory syncytial v irus (RSV) antibody status on frequency and severity of RSV infections in children with underlying heart or lung disease. Design. Cohort stu dy conducted during two consecutive RSV seasons. Setting. Ambulatory p atients at eight Canadian pediatric tertiary care centers. Methods. Su bjects under 3 years old with underlying heart disease who were digoxi n-dependent or had not received corrective cardiac surgery or with und erlying lung disease were enrolled. Demographic information and an acu te sera for RSV neutralizing antibody was obtained on enrollment. Week ly telephone follow-up consisting of a respiratory illness questionnai re was followed with a home visit to obtain a nasopharyngeal aspirate when there was new onset of respiratory symptoms. The specimen was use d to detect RSV antigen. RSV illnesses were grouped as upper or lower respiratory tract infection (LRI) based on clinical and radiographic f indings. RSV hospitalizations were considered to be those RSV infectio ns that resulted in hospitalization. Results. Of 427 enrolled subjects , 160 had underlying lung disease only, 253 had underlying heart disea se only, and 14 had both. Eleven percent and 12% of lung and heart dis ease groups, respectively, had an RSV LRI. Three percent and 6% of lun g and heart disease groups, respectively, were hospitalized with RSV i nfection. A significant decrease in frequency of RSV LRI and RSV hospi talization occurred with increasing age, with a major drop in those ol der than 1 year vs those younger than 1 year. Acute sera were availabl e from 422 subjects. Geometric mean RSV antibody titers demonstrated a U-shaped distribution with increasing age. The trend to lower antibod y concentrations in premature infants did not reach statistical signif icance. The frequency of RSV infection and RSV LRI was lower in patien ts with antibody at a titer more than 100, although the difference for RSV hospitalization was not statistically significant. These differen ces remained significant after age adjustment. Conclusion. Both age an d RSV antibody status impact on RSV illness and LRI. Reduction in illn ess frequency with increasing age may lead to more informed targeting of those children most likely to benefit from RSV immune globulin prop hylaxis.