Reliability of the Direct Fluorescence Assay Compared to the Real-time RT-PCR as Respiratory Syncytial Virus Diagnostic Tool

Lower respiratory tract infections (LRTIs) are the leading cause of morbidity and mortality among
children under five years of age. Worldwide, Respiratory syncytial virus (RSV) is considered the most
common cause of LRTIs among young children. There are various detection methods for RSV
available in the market, two of them, the direct fluorescence assay (DFA) and the real-time reversetranscription
polymerase chain reaction (rt-RT-PCR) were compared in our study. The DFA provides
same-day results, and the rt-RT-PCR is widely used in research laboratories because of its superior
sensitivity; however, rt-RT-PCR is cost prohibitive in many clinical settings, particularly in newly
industrialized and developing nations.
We collected 450 nasopharyngeal aspirates from children 5 years of age or less and tested for RSV
using both methods. The overall prevalence rate of the RSV among the children was 23.8% with a
significantly higher prevalence among children under the age of 6 months of age when compared to
other age groups. The sensitivity of DFA in comparison to rt-RT-PCR was highest (86%) during the
first 3 days of symptoms onset and decreased gradually till it reached 65% after the first week. The
specificity of DFA in comparison to rt-RT-PCR ranged between 99 and 100% irrespective of the date
of collection. We concluded that, although the rt-RT-PCR is more sensitive for RSV detection, the
DFA offers a reliable point-of-care alternative detection method especially during the first few days of
illness. Therefore, the DFA can be used as an early detection tool for RSV where rt-RT-PCR is
unavailable.