Paragraph: the aetiology of community-acquired pneumonia (cAp) is not easy to establish. As lung ultrasound (LUS) has already proved to be an excellent diagnostic tool for cAp, we analysed its usefulness for discriminating between the aetiologically different types of CAP in children. We included 147 children hospitalized because of cAp. LUS was performed in all patients at admission, and follow-up LUS was performed in most patients. LUS-detected consolidations in viral CAP were significantly smaller, with a median diameter of 15 mm, compared to 20 mm in atypical bacterial CAP (p = 0.05) and 30 mm in bacterial cAp (p < 0.001). Multiple consolidations were detected in 65.4% of patients with viral CAP and in 17.3% of patients with bacterial CAP (p < 0.001). Bilateral consolidations were also more common in viral CAP than in bacterial CAP (51.9% vs. 8.0%, p < 0.001). At follow-up, a regression of consolidations was observed in 96.6% of patients with bacterial CAP and in 33.3% of patients with viral cAp (p < 0.001). We found LUS to be especially suitable for differentiating bacterial CAP from CAP due to other aetiologies. However, LUS must be interpreted in light of clinical and laboratory findings. Childhood community-acquired pneumonia (CAP) is a common infection of the lower respiratory tract and the single most important cause of mortality in preschool children in the developing world 1 . In the developed world, CAP is imposing a significant burden of morbidity, with an estimated annual incidence of 14.5 per 10,000 children from 0 to 16 years old 2 . The diagnosis of CAP in children can be challenging as there is no pathognomonic sign or symptom 3 . Respiratory viruses are the most common cause of CAP in preschool children, followed by bacteria, especially Streptococcus pneumoniae. The atypical bacteria Mycoplasma pneumoniae and Chlamydophila pneumoniae are common causes of pneumonia in children older than 5 years 4 . The identification of the causal agent is pivotal, especially in children who require hospital admission, as it guides the choice of appropriate treatment. However, the microbial diagnosis of CAP in children is not easy to establish without invasive procedures, which are only rarely performed in this age group 2,5 . Pneumonia can be a life-threatening disease if left untreated 6 . Initially, antibiotic therapy is empirical and influenced by epidemiological, clinical and radiographic findings. Slovenian guidelines recommend a penicillin-based antibiotic as a first-line therapy for non-complicated bacterial CAP in the paediatric population. Macrolide antibiotics should be used for the presumed atypical bacterial CAP 7 . Children with non-complicated viral CAP need only supportive treatment 6 . Clinical features of bacterial pneumonia, atypical bacterial pneumonia or viral pneumonia frequently overlap and cannot be used reliably to distinguish between the various aetiologies 8 . The same applies to blood tests such as the complete blood count (CBC) with differential and acute phase reactants. Normal white blood cell (WBC) count and low C-reactive protein (CRP) do not exclude bacterial CAP 6 . On the other hand, a low serum procalcitonin (PCT; <0.25 ng/ml) was recently found to have a 96% negative predictive value (95% confidence interval [CI], 93-99), 85% sensitivity (95% CI, 76-95), and 45% specificity (95% CI, 40-50) in identifying children without typical bacterial CAP 9 . 
 Title: the Usefulness of Lung Ultrasound for the Aetiological Diagnosis of community-Acquired pneumonia in children
Output: True