Etiology and outcome of severe community acquired pneumonia in immunocompetent adults

Background: Community Acquired Pneumonia (CAP) is a commonly encountered disease, one third of which is Severe Community Acquired Pneumonia (SCAP) that can be potentially fatal. There is a paucity of data on etiology and outcome of patients with SCAP in South Asian Population. Methods: A retrospective cross-sectional study was conducted from March 2002 till December 2008 on patients of 16 years and above who were admitted with the diagnosis of SCAP in accordance to the criteria of American Thoracic Society Guidelines (2001). The patients underwent clinical and diagnostic evaluations to detect the severity of illness as well as the etiology and other risk factors influencing the eventual outcome of SCAP. Results: A total of 189 patients were included in the study. The mean age was 60 +/- 18.0 years and 110 (58%) patients were males. The most common isolated pathogens were Staphylococcus aureus (15 patients), Streptococcus pneumoniae (14 patients) and Pseudomonas aeruginosa (9 patients). The highest mortality was seen in patients with Pseudomonas aeruginosa (89%) and Staphylococcus aureus (53%). Overall mortality rate was 51%. On univariate analysis, septic shock (p < 0.001), prior antibiotic use (p = 0.04), blood urea nitrogen > 30 mg/dl (p = 0.03), hematocrit < 30% (p = 0.03) and Acute Physiology and Chronic Health Evaluation (APACHE) II score > 20 (p < 0.001) were significantly different between the patients who survived as compared to those who did not. On multivariate analysis, septic shock (p < 0.001, OR: 4.70; 95% CI= 2.49-8.87) was found to be independently associated with mortality. Conclusion: The microbes causing SCAP in our study are different from the usual spectrum. Staphylococcus aureus and Pseudomonas aeruginosa were the common causative pathogens and associated with high mortality. It is important to establish clinical guidelines for managing SCAP according to the etiologic organisms in our setting.