The objective of this study was to assess the diagnostic accuracy of oropharyngeal (OP) cultures relative to simultaneous bronchoalveolar lavage (BAL) cultures in very young children with CF, and to examine the effects of bacterial density, age, and study cohort on diagnostic accuracy. Respiratory culture data were analyzed from three independent, prospective studies involving simultaneous collection of 286 OP and BAL cultures from 141 children with CF <5 years of age. For predicting any growth of Pseudomonas aeruginosa (Pa) from the lower airway in subjects </=18 months of age (mean age, 8 +/- 5 months), OP cultures had a sensitivity of 44% (95% CI 14%, 79%), specificity of 95% (90%, 99%), positive predictive value of 44% (14%, 79%), and negative predictive value of 95% (90%, 99%). Diagnostic accuracy was similar for Haemophilus influenzae (Hi). Specificity was significantly lower for Staphylococcus aureus (Sa). Sensitivity for all organisms improved if a positive lower airway culture was defined as >/=10(3) or >/=10(5) cfu/mL. Specificity for Pa declined significantly with increasing age. In children with CF <5 years of age, the specificity and negative predictive value of OP cultures for Pa are high, while the sensitivity and positive predictive value are poor. Thus, in this age range, a negative throat culture is helpful in "ruling out" lower airway infection with Pa. However, a positive culture does not reliably "rule in" the presence of Pa in the lower respiratory tract. These findings may have implications for study design and interpretation as well as clinical management of young children with CF.
Copyright 1999 Wiley-Liss, Inc.