In this retrospective study we evaluated the diagnostic value and the clinical relevance of detecting 19 viruses and Mycoplasma pneumoniae in symptomatic pediatric patients attending a pediatric outpatient clinic, emergency department or admitted to the pediatric ward of a large general hospital. At least one respiratory pathogen was detected in 73% of the enrolled patients. These findings are in support of the reports in the literature were viral detection rates of 47-95% are described in children. Possible explanations for the wide differences in detection rates in the literature include heterogeneity in study populations, differences in presenting respiratory symptoms (upper or lower respiratory symptoms), number of respiratory pathogens tested, method used for detection and genetic variability between populations [1, 16–18]. RSV and HRV were the most common viruses detected in this patient group, FLUAV and HPIV-2 were not detected during the year. HPIV-2 was possibly not detected due to a biennial cycle of HPIV-2. A plausible explanation for the lack of detection of FLUAV is the fact that the influenza A(H1N1)pdm09 circulated earlier (October-December 2009) than expected and our study was conducted in 2010 and another explanation for the low incidence is the result of a nationwide successful (> 95% coverage) large influenza vaccination campaign against influenza A(H1N1)pdm09 in 2009 for children aged between 6 months to 4 years.
Overall, in 27% of the patients, multiple respiratory viruses were found, comparable to other studies were the co-infection rate ranged from 17% to 41% [17, 19]. As expected, the majority of the respiratory pathogens were detected in the younger patients. The higher detection rate of respiratory pathogens among younger children has been ascribed to a higher infection rate, lower viral clearance rate due to a still developing specific immune system against these viruses and higher infection pressure associated with day care attendance and living conditions such as crowding [1, 2, 20–22]. Furthermore, the parents of younger children may seek healthcare earlier in the course of disease due to parental anxiety.
The recent introduction of more sensitive molecular methods in the clinical practice has increased the virus detection rates significantly compared to viral culture methods. This has, however, made the interpretation of positive test results more difficult, especially when multiple viruses are found with a low Ct value. Nevertheless, the detection of a virus by RT-qPCR does not necessarily means that it causes symptoms. The presence of a virus, particularly HRV, has to be interpreted carefully as viral RNA could be detected in nasal mucus for up to 5–6 weeks after infection and respiratory viruses are also detected in asymptomatic children [23, 24]. For newer viruses, such as WUPyV and KIPyV, causality of respiratory disease remains unclear. Until their role in respiratory disease is known inclusion in a respiratory panel for diagnosis may not be warranted.
In literature conflicting results are reported regarding multiple viral co-infections and its association with the severity of acute disease. In this study, 66.6% of the HRV positive patients HRV was co-detected with another virus compared to 42% of the RSV cases. In addition, most samples with more than 1 virus, HRV and RSV were detected together, in 12 (25.5%) of the 47 samples, respectively. Similar to our data, Aberle et al.  found HRV and RSV together in 35.9% of the dual infections and Advani et al.  found that in 73% of the co-infections HRV was involved. On the other hand, Greer et al.  found HRV in a much lower co-detection rate of 23.6%. Some studies have demonstrated that multiple viral pathogens cause more severe disease [1, 17], whereas others did not find any difference in disease severity between the detection of a single and multiple respiratory viruses in respiratory samples, not even with the combination of RSV and HRV [16, 19, 26]. The present findings support the latter conclusion. We found that patients with multiple respiratory viruses even had a shorter duration of hospitalization and were more likely to have non-respiratory symptoms as diarrhea, vomiting and feeding problems. This is similar to the observation of a shorter duration of hospitalization in patients with RSV/HRV dual infections compared to those with a single infection with RSV by others [19, 27]. This suggests that HRV may have a potential protective effect on disease severity. This may be explained by the possible protection of the induced immune response trigged by viral infection from infection with a second virus as postulated by Greer et al.  where HRV could protect its host from infection by other viruses.
Detection of a virus in patients with respiratory symptoms would be expected to aid a clinician to refrain from the prescription and continuation of antibiotics. Unfortunately, as shown by the present study this is not the real life clinical practice as only in 40% the antibiotic treatment was ceased. The present findings confirm previous reports that have shown that detection of a viral respiratory pathogen in a large part of the pediatric patients did not influence a change in antibiotic management of individual patients [15, 28]. This may be attributed to the young age of the children, severity of clinical symptoms and the general attitude of clinicians to complete antibiotic treatment in children due to concern about bacterial co-infections and development of antibiotic resistance. Identification of viral pathogens can be of importance for both individual patient management and hospital infection control policy. Rapid diagnosis could contribute to a significant reduction in unnecessary laboratory tests and costly imaging, especially in young children, thereby decreasing diagnostic costs. Bonner et al.  demonstrated this together with a decreased length of time to discharge in a study were the impact of a rapid influenza test result was determined on patient management. Rapid and sensitive diagnosis of viral infections is also thought to be important to reduce nosocomial transmission as all patients infected with a respiratory virus need to be isolated (contact or droplet precautions). All these data suggest that routine molecular testing for respiratory viral pathogens could be useful to decrease the duration of hospitalization and reduce nosocomial infections.
In addition, in specific patient populations, e.g., after stem cell transplantation or with immunosuppression, identification of the viral pathogen can be important in predicting the clinical course, preventing graft-versus-host disease and graft rejection and, even lifesaving [30, 31].