The Value of Ultralow Dosis CT and Ultrasound in the Diagnosing of Pneumonia in the Emergency Department

Community-acquired pneumonia (CAP) is one of the most common infectious diseases in the emergency department (ED). In Denmark, the incidence of hospitalization is 809 per 100,000 and 30-day mortality is 13%. In 2018, 29.5 per 100.000 people died of pneumonia. An increase from 27.7 per 100,000 in 2017. CAP is usually suspected in patients with dyspnea, cough and fever, without other probable explanations or when other differential diagnosis is less likely. However often patients present with vague and uncharacteristic symptoms such as altered state of consciousness, gastrointestinal symptoms or pain. Likewise is fever not always present in the elderly. The most common CAP pathogens are Streptococcus pneumoniae, Haemophilus influenzae, and gram-negative bacilli. Other notable microbiological pathogens include viruses such as Influenza, COVID-19, parainfluenza and respiratory syncytial virus. Viruses are associated with bacterial co-infections, leading to increase mortality and complications such as admission to the ICU. Normally, when a pulmonary infection is suspected, a chest X-ray is performed. Chest x-rays have a sensitivity of 43,5% (39,4-50,8) and a specificity of 93% (92.1-93.9) for pulmonary opacities compared to CT. A chest x-ray has a sensitivity of 79% for pneumonia. Computed tomography (CT) scan of the thorax has higher diagnostic precision and results improve management but result in a correspondingly increased amount of radiation compared to chest X-ray. An ultra-low-dose CT (ULD-CT) scan of the thorax may be an alternative to CT scan. ULD-CT has a radiation dose of approx. 1.5 times greater than the radiation dose of a chest X-ray and approx. 1.5% of a CT scan. ULD-CT has shown better image quality than chest X-ray, and for acutely admitted patients with dyspnea, it has a clinical effect on both diagnosis and treatment. Like chest X-rays, basic findings on ULD-CT of the thorax can be interpreted by trained clinicians.

Ultrasound is a fast non-invasive diagnostic test, without radiation. LUS has high sensitivity and specificity, with the area under ROC (AUC) of 0.95-0.98 for pneumonia. A meta-study for the use of LUS in the diagnosis of pneumonia in the ED has shown a sensitivity of 92% (87-96%) and a specificity of 94% (87-97%). AUC was calculated at 0.97. The ultrasound operators in the meta-study were all experienced ultrasound operators. Ultrasound is an operator-dependent tool and in children, it has been demonstrated that LUS diagnostic accuracy for pneumonia, is significantly lower when performed by a novice sonographer compared to an advanced sonographer. There are few if any studies that have investigated the diagnostic accuracy of novice LUS operator, in the ED, for pneumonia.

Study goals and objectives The project is divided into two, a ULD-CT study and an LUS study. The study will aim to investigate their diagnostic capabilities in at emergency department setting.

The main objective of the ULD-CT study is to investigate and answer:

• Can ULD-CT be used to diagnose pneumonia in the emergency department?
• How is the agreement between the results from ULD-CT and results from HR-CT
• Is ULDCT more sensitive and specific than standard chest x-ray in the diagnosis of pneumonia?