Objective: Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infections (LRTI) in children. This study was aimed to investigate the presence of RSV by cell culture and direct fluorescent antibody (DFA) methods in children with LRTI and to evaluate the results in association with the clinical findings of the patients.

Materials and Methods: The study included 162 children with LRTI. The age group of the cases was 0-5 years old, of which 107 were outpatients and 55 were inpatients. Nasopharyngeal swab samples were obtained by flocked swabs and transported to the laboratory within the viral transport medium (Copan Diagnostics, Brescia, Italy). Samples were inoculated into the shell-vial cell culture prepared with A549 cells and presence of RSV were investigated in the fixed cells by fluorescence-labeled monoclonal antibodies (Anti-RSV Group FITC, Argene, BioMérieux, France) after 48-72 hours of incubation. For the DFA method, slides were prepared directly from the samples with cytospin centrifuge method and RSV was investigated following staining with fluorescent labeled monoclonal antibodies in a similar way. Samples which yielded discordant results with cell culture and DFA test, RSV RNA was investigated by a commercial real-time polymerase chain reaction (RT-PCR) kit (RealStar RSV RT-PCR Kit, Altona Diagnostics, Germany). In addition, symptoms, physical examination and laboratory findings together with the treatment outcome of the patients were recorded.

Results: RSV was detected in 26.5% (43/162) of the samples by cell culture. Both cell culture and DFA detected RSV in 24.3% (38/162) of the samples while 71.0% (115/162) were negative with both tests. Five RSV cell culture positive samples were negative with DFA, and four positive samples with DFA were negative with cell culture. In these nine samples, the RSV PCR test results were consistent with the cell culture test results. When the cell culture method was considered as the reference method, sensitivity, specificity, positive (PPV) and negative predictive values (NPV) for the DFA method were 88.4%, 96.6%, 90.5% and 95.8%, respectively. The average age of the RSV-positive patients (11.2±11.3 months) were significantly lower than that of RSV-negative patients (21.7±18.6 months) (p=0.001). There were no significant difference in terms of gender, symptoms, physical examination, treatment outcome and other laboratory markers (CRP, leukocytosis, increase in neutrophile count, lymphocytosis and thrombocytosis) between RSV positive and negative patients (for all p>0.05). The analysis of the RSV test requests revealed that 93.8% of the requests were in January, February and March, and all positive cases were detected in these months.

Conclusion: In conclusion, RSV was detected in 26.5% of 0-5 years old children with LRTI and this rate was significantly higher in early ages. DFA method which has a high sensitivity and specificity in the diagnosis of RSV infection, ensures rapid diagnosis and enables the evaluation of the quality of respiratory samples.