Laboratory Diagnosis of Acute Lower Respiratory Tract Viral Infections in Children

This report summarizes and compares the results of complement fixation test (CFT), virus isolation (VI), and direct immunofluorescence test (DIF) for the antigen detection of respiratory syncytial virus (RSV), influenza A virus (Flu A), and adenovirus in 62 children with acute lower respiratory tract infections (ALRI) in Kuwait. It includes, as well, CFT results for parainfluenza virus and Mycoplasma pneumoniae. Combining the three methods, a potential causative agent was identified in 56 (90 per cent) children, of whom 14 (22 per cent) had evidence of infection with more than one pathogen. RSV was most frequently identified followed by Flu A, parainfluenza, Mycoplasma pneumoniae and adenovirus. Virus isolation proved the best method for identification of RSV, Flu A, and adenovirus [identified 52 (84 per cent) cases]. DIF was sensitive for RSV detection (sensitivity 84 per cent, specificity 94 per cent), and less sensitive for Flu A (sensitivity 62 per cent, specificity 98 per cent). However, DIF was completely insensitive to adenovirus (no positives). CFT was positive for the five pathogens in 44 (71 per cent) of the population studied; therefore, almost 20 per cent of positive identifications would have been missed if VI and DIF were not done. The sensitivity and specificity of CFT for RSV, adenovirus and Flu A were 71, 75, and 31 per cent, and 94, 96, and 94 per cent, respectively. Based on the results of this pilot study, it appears that a combination of the three tests yields the best rate of virus detection. Cell culture cannot be discarded for the identification of some respiratory viruses, especially adenovirus, until better techniques, or more sensitive reagents are applied. However, since RSV is the virus most commonly involved in children with ALRI, we recommend using DIF on routine basis for diagnosis. Its results compare well with virus isolation; it is simple, rapid, and inexpensive.