The onset of HAdV in children remains controversial, and the results of this study based on 5,989 cases found that the peak periods of disease onset were in December, January, May, and June, while the underestimation periods were in August, September, October, and November. This result suggested that the onset of adenovirus was significantly correlated with climatic factors. Moreover, the most common age of children infected by HAdV was 6.0 months or older. Finally, the risk of co-infection for children was influenced by the duration of hospitalization and the procalcitonin level.
In this study, we noted that 73.6% of the children with respiratory disease presented with bronchiolitis, and their clinical manifestations were similar to those of “influenza,” including cough, runny nose, and fever. Of the remaining patients, 17.6% presented with bronchopneumonia and 8.8% presented with severe pneumonia. The clinical manifestations of these cases included persistent high fever, dry cough, shortness of breath, and hypoxemia, which were associated with a high incidence of mortality. This result was consistent with the findings of a previous study conducted in Korea . Furthermore, the fever duration ranged from 0 to 13 days, and the mean temperature fluctuated from 37.4 °C to 39.4 °C, which was not consistent with the study conducted by Xie et al. , who noted that the temperature fluctuated from 40.0 °C to 40.9 °C in most children; the disease duration ranged from 3.0 to 14.0 days; and most cases entered the recovery period after 2.0 weeks.
Most cases presented mild symptoms at the early stage, and 73.6% of the children showed bronchiolitis. The imaging characteristics in these cases included increased and thickened main veins in the two lungs and a higher frequency of interstitial reticular shadows in the lower lobes of the two lungs. Moreover, the characteristics of the moderate to severe cases included multiple clusters of consolidation shadows in both lungs, "centripetal" lesions that were mainly found in the middle and inner lungs, more fusion foci, more large foci, more emphysema, more lung texture, fewer round foci, fewer pulmonary bullae, and less pleural effusion, which were associated with rapid progression, and multiple clusters of consolidation shadows in both lungs. Although the cases with moderate to severe symptoms presented with "centripetal" lesions, they showed no obvious irregularity in the distribution and morphology of the bronchial tree. Finally, we did not find positive cases for encephalitis, indicating that HAdV infections did not involve the central nervous system. These characteristics could differentiate HAdV infections from H1N1 infections, since H1N1 tends to distribute along the central bronchial tree with an intact bronchial tree shape. Moreover, the H1N1 virus can easily invade the central nervous system, yielding positive images of the central nervous system, and may even cause necrotizing encephalitis.
In this study, the duration of hospitalization and procalcitonin were suggested to affect the risk of co-infection in children with HAdV infections. The potential reason for this could be that a longer hospital stay was associated with severe symptoms. Moreover, the increased level of procalcitonin could protect against the risk of co-infection, which were inconsistent with previous studies . The level of procalcitonin could distinguish the infections by viral and bacterial, and the value of procalcitonin should combined with CRP and the clinical manifestations of HAdV infections [17, 18]. Finally, increased LDH levels might be associated with an increased risk of co-infection, although this association was not found to be statistically significant in the present study. A potential reason for this could be that an elevated LDH level may indicate damage to lung tissue, and is a biomarker for predicting the severity of infection [19, 20].
Several limitations of this study should be acknowledged: (1) Since this study had a retrospective design, uncontrolled biases affecting the reliability of the results might have been present; (2) the data available in the current study were based on electronic medical records, while the background therapies were not addressed; (3) stratified analyses based on the characteristics of patients were not conducted owing to the small number of patients in each group; (4) the serotype of the adenovirus, which could affect the clinical manifestations and severity of the disease, was not addressed in this study.