BACKGROUND AND AIM: Atypical pneumonia involves viral and some bacterial microorganisms in etiology. As Coronavirus 2019 (COVID-19) is newly identified, the differences between coronavirus and other microorganisms causing atypical pneumonia have not been fully expressed yet. We aimed to make a clinical comparison of cases with COVID-19 and atypical pneumonia.

METHODS: “Non-COVID-19 atypical pneumonia” (non-COVID) group included patients with both radiological and clinical confirmation of atypical pneumonia by radiologists and clinicians. Patients with a positive polymerase chain reaction test formed “COVID-19 pneumonia” (COVID) group. Demographics, radiological, laboratory, and clinical features were recorded retrospectively.

RESULTS: A total of 177 patients (46 non-COVID and 131 COVID) were included. The mean age of the COVID group was significantly lower (p=0.040). Ground-glass density and peripheral involvement were more common in thoracic computed tomography of patients with COVID-19 (p=0.017 and p=0.019). Fever and fatigue in COVID (p<0.001 and p=0.040) and shortness of breath and gastrointestinal complaints in non-COVID group were significantly higher as presenting symptoms (p<0.001 and p=0.031). In biochemical tests, impairment in liver function tests in COVID-19 (p<0.001), impairment in kidney function tests, increased C-reactive protein (CRP) and procalcitonin (PCT) in non-COVID-19 patients were more common (p=0.003, p=0.042, and p=0.023, respectively). Serum PCT, CRP, and lymphocyte levels were significantly lower in cases with COVID-19 (p<0.001, p=0.048, and p=0.016). There was no significant difference in the prognosis of both groups (p=0.556).

CONCLUSIONS: With COVID-19 pandemic, there has been an increase in atypical pneumonia cases in which viral strains play a role. Symptomatic, laboratory, and radiological differences between two groups detected in our study may help in differential diagnosis especially in winter when atypical pneumonia is more common.