Serial Procalcitonin Levels and Bacterial Etiology in Hospitalized Patients with Community-Acquired Pneumonia

Background: Accurate determination of the microbial etiology of pneumonia has important consequences for appropriate administration of antimicrobials and antimicrobial stewardship. Procalcitonin (PCT) is a biomarker that is finding increasing diagnostic and prognostic utility in lower respiratory infections, however, it remains unclear whether it can be helpful in predicting the bacterial etiology of pneumonia. In this study, we examined the relationship between serial PCT measurements and bacterial etiology in hospitalized patients with community-acquired pneumonia, including those at high risk for infections due to multi-drug resistant organisms (MDRO), to determine whether PCT at admission and its trajectory early in the hospital course of patients provides distinguishing information between different bacterial causes of pneumonia.Methods: We analyzed data collected from a prospective cohort study of 505 patients admitted to a tertiary care center with a clinical syndrome consistent with pneumonia. Bacterial etiology of pneumonia was determined from high quality respiratory samples, blood cultures and other relevant diagnostic tests according to standard protocols in conjunction with clinical review. Daily plasma procalcitonin levels were measured for these patients serially during the first four days of hospitalization. We compared procalcitonin levels associated with different bacterial etiologies of pneumonia over the first four days of admission, using the Mann-Whitney-U test to assess for statistical significance.Results: Out of 505 patients, the diagnosis of pneumonia was adjudicated in 322, and bacterial etiology determined in 64 cases. The predominant pathogens were Staphylococcus aureus (n = 19; 12 Methicillin Resistant (MRSA) and 7 Methicillin Susceptible (MSSA)), Pseudomonas aeruginosa (n = 12), Streptococcus pneumoniae (n = 6), and Haemophilus influenza (n=5). We found higher procalcitonin values for S. pneumoniae relative to other etiologies, a delayed rise for Pseudomonas over time, and consistently low PCT values for infections due to multiple bacteria. In addition, our results also suggest that procalcitonin values on the second day of hospitalization, rather than at admission, may have the most utility in distinguishing between bacterial etiologies.Conclusion: Serial procalcitonin values during the early course of bacterial pneumonia reveal a difference between pneumococcal and other bacterial etiologies, and may have an adjunct role in guiding antibiotic choice and duration.