Utility of Direct Fluorescent Antibody Testing of Nasopharyngeal Washes in Children With and Without Respiratory Tract Illness

Abstract

Direct fluorescent antibody (DFA) testing of nasopharyngeal wash specimens is a rapid and reliable means of diagnosing respiratory viral infection. The utility of DFA testing in the evaluation of febrile children without respiratory symptoms has not been critically evaluated. It is not known whether clinical or demographic factors apart from respiratory symptoms are associated with a positive DFA or whether a positive DFA is more likely to be associated with lower or upper respiratory tract symptoms (RTS). This is a retrospective case-series of 756 consecutive nasopharyngeal specimens with respiratory DFA testing performed at the University of California San Francisco from November 1, 2002 through October 31, 2003. No RTS was a statistically significant predictor of negative DFA [odds ratio (OR), 0.03; 95% confidence interval (CI), 0.004-0.2; P = 0.001] compared with lower RTS. Male subjects were more likely than female subjects to have a positive DFA (OR 1.8; 95% CI 1.1-2.8; P = 0.02). Specimens collected from April to October were less likely to have a positive DFA (OR 0.4; 95% CI 0.2-0.7; P = 0.001). Specimens collected at the time of hospital admission and during a hospitalization were less likely to have a positive DFA (OR 0.5; 95% CI 0.3-0.9; P = 0.01 and OR, 0.07; 95% CI 0.02-0.2; P = 0.001, respectively) compared with specimens collected in the outpatient setting. The yield of testing children without respiratory tract illness is extremely low.