Introduction: The prognosis of community acquired pneumonia (CAP) varies from one patient to another. It is the leading infectious cause of morbidity and mortality in developing countries. The factors that determine the prognosis of CAP are poorly understood. Indeed, few studies have attempted to determine these factors.

Objectives: Assess the prognostic factors of CAP including patient characteristics, vital signs, biology, radiology and the use of initial antibiotic therapy.

Methods: Observational descriptive study that included patients who have had a CAP from January 2014 to May 2022 in pulmonary department I of Abderrahmane Mami Hospital. The judging criteria of a poor prognosis was: 30-day mortality, intensive care unit hospitalization and short-term (30-day) complications.

Results: A total of 125 patients were enrolled. The 30-day mortality was 5.6% (7 patients).

Nine patients (7.2%) were transferred to the medical intensive care unit. Complications were noted in 36 patients (28.8%) and were mainly represented by: renal failure, cardiac decompensation, radiological aggravation with ARDS, shock and purulent pleurisy.

Thirty-six patients (28.8%) had a poor outcome and prognosis. In multivariate analysis Factors of a poor prognosis were: Age more than 58 (p=0.011). A white blood cell count above 15000 (p=0.0068). Hypercapnia>44 (p=0.0002). A PSI score > 79 and a CURB-65 score >1 respectively (p <0.0001) and (p=0.0001). PSI score was more sensitive (sensitivity=83.33; specificity=62.07) while CURB-65 was more specific (sensitivity=58.33;specificity=78.41).

Conclusions: According to our study, CAP can be severe even in a middle-aged adult in the presence of hypercapnia and hyperleukocytosis. Prognosis scores are reproducible tools to assess objectively the prognosis of CAP.