Table 1 shows a detailed summary of data obtained for each winter season.

During the 2022/2023 winter season, 45 children with upper respiratory tract infection underwent MRI and 44 had a CT scan. Both MRI and CT examinations were performed in 23 patients, resulting in a total of 112 patients (57 males; mean age 6 ± 5 years, median age 5.5 years), who were included in the study.

These 112 cases of cross-sectional imaging in children with upper respiratory tract infections in the 2022/2023 winter season were significantly more than expected based on the data from the winter seasons of the preceding five years, in which the respective mean was 32 cases (P<0.001). The following complications were detected: mastoiditis, abscess, phlegmon, meningitis, reactive vasculitis, and sinus vein thrombosis. Abscesses were predominantly located periauricular, intracranial, and periorbital. Phlegmons were diagnosed using MRI and were, by far, most frequently located in the orbit/periorbital area, occasionally in cervical or other facial localizations, such as the nose or cheek. Reactive vasculitis, which was diagnosed in MRI, affected the petrous and cavernous segment of the internal carotid artery characterized by vessel wall thickening and consecutive luminal narrowing. Sinus vein thrombosis was found in the sigmoid and transverse sinuses and partly extended into the internal jugular vein.

The number and rate of complications diagnosed by imaging were also significantly higher than expected based on the data from previous winter seasons, with a complication rate of 92% (mean of prior years, 75%; P<0.001). The complication rate was higher at younger ages with 98% in children younger than 4 years, 95% in children under 7 years, and 87% from 7 years old (P=0.026).

Each of the complications assessed showed a significant increase during the winter season of 2022/2023. Severe complications especially increased during the first post-pandemic winter season. For example, vascular complications (sinus vein thrombosis and reactive vasculitis) increased from only five cases within the prior five years to 11 cases during the 2022/2023 winter season. Reactive meningitis as a complication of upper respiratory tract infection increased from four cases in the prior five winter seasons to eight cases during the post-pandemic winter season. Table 1 provides an overview of the number of cases of each imaging-based complication recorded per winter season. Figures 1, 2, 3, 4, 5, 6, 7, and 8 show examples of each of the assessed complications from the 2022/2023 winter season.

Coronal T1-weighted magnetization prepared-rapid gradient echo sequence magnetic resonance image after intravenous contrast agent administration in a 5-year-old girl with a sinus vein thrombosis in the right sigmoid sinus (arrow) caused by mastoiditis

Axial post-contrast computed tomography image (soft tissue window) in a 2-year-old girl with a sinus vein thrombosis in the left sigmoid sinus (arrowhead) and a retroauricular abscess (arrow) caused by mastoiditis

Axial T1-weighted magnetization prepared-rapid gradient echo sequence magnetic resonance image after intravenous contrast agent administration in an 8-year-old boy with osteomyelitis of the frontal bone as a complication of acute sinusitis of the frontal sinus and ethmoidal cells. Subperiosteal abscess on the forehead (Pott’s puffy tumor, thick arrow) and frontal epidural and subdural abscesses (arrowheads) are visible as well as accompanying cerebritis of the right-sided gyrus frontalis inferior (asterisk) and accompanying meningeal reaction (thin arrows)

Axial multi-slab of a time-of-flight angiography 3-dimensional sequence magnetic resonance image without contrast agent administration in a 5-year-old girl with extensive abscess at the left skull base with reactive vasculitis of the internal carotid artery in the petrous part M1 (arrow) as a complication of otitis media and mastoiditis

Axial T2-weighted turbo-spin-echo sequence magnetic resonance image with fat-saturation without contrast agent administration in a 2-year-old girl with a right-sided periorbital phlegmon as a complication of acute sinusitis

Axial T2-weighted turbo-spin-echo sequence magnetic resonance image with fat-saturation without contrast agent administration in an 8-year-old girl with mastoiditis (arrowhead). There is a concomitant abscess (arrow) on the right

Axial computed tomography image (bone window) without contrast agent administration in a 13-year-old boy with right mastoiditis (asterisk) and osseous destruction (arrow) and extraosseous periauricular abscess (arrrowhead)

Axial computed tomography image (soft tissue window) without contrast agent administration in a 7-year-old boy with a left retrotonsillar abscess due to tonsillitis (arrow)

Regarding the results of pathogen testing, the rate of detected bacterial infections did not significantly differ within the 6-year period studied (P=0.053). Streptococci (especially, Streptococcus pyogenes, intermedius, pneumoniae, constellatus) made up the majority followed by staphylococci (particularly Staphylococcus aureus, epidermidis, and auricularis) and bacillus species. However, the rate of cases with detected bacterial infection with streptococcal species in 2022/2023 winter season was 76%, significantly higher than it was expected based on the prior five winter seasons with a mean rate of 62% (P=0.010). Complications arose in all confirmed streptococcal infections and streptococci were detected in most serious complications, such as abscesses and intracranial difficulties. There was also a significant increase in the rate of surgical treatment, including functional endoscopic sinus surgery, mastoidectomy, adenectomy, paracentesis with insertion of a tympanic drainage, abscess clearage (intracranial, cervical), tonsillectomy, and combinations thereof, in pediatric cases with complications of upper respiratory tract infections visualized by MRI and CT (P=0.023).

During the first complete pandemic winter season in Europe (2020/2021), the number of MRI and CT scans in children with upper airway infections decreased significantly to 20 cases compared to a mean of 33 cases in the pre-pandemic years, 39 cases in the second pandemic year, and 112 cases in the first post-pandemic winter season (P<0.001). Additionally, the complication rate (P=0.002), the rate of detected streptococcal infections (P<0.001), and the rate of surgery (P=0.012) decreased significantly in the 2020/2021 winter season compared to the other winter seasons assessed. In the second pandemic winter season, the numbers and rates recovered to pre-pandemic levels.

The CRP level was lowest in 2017/2018 and highest in 2020/2021, which is a statistical significant difference (P<0.001). Leukocytosis did not differ significantly between the years (P=0.101).