What is included in the workup of pneumococcal pneumonia?

Updated: Jun 08, 2020
  • Author: Eduardo Sanchez, MD; Chief Editor: John L Brusch, MD, FACP  more...
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Many patients with pneumonia are treated empirically. Antibiotics used in these cases should include those that cover S pneumoniae. In severe, unusual, or complicated cases or those that require hospitalization, an attempt to obtain sputum cultures should be made. [58] An acceptable sputum sample is indicated by the presence of few epithelial cells and many polymorphonuclear neutrophils (a ratio of 1:10-20). The presence of many gram-positive cocci in pairs and chains on Gram stain of sputum provides good evidence for pneumococcus. When large effusions/empyema is present, pleural fluid should be obtained for Gram stain and culture.

The yield of blood cultures in pneumonia is relatively low. The most common bacteria isolated is S pneumoniae. Blood cultures are not indicated in all hospitalized patients with CAP, but they should be obtained in patients with severe pneumonia, immunocompromise (alcohol abuse, leukopenic, liver disease, asplenia, HIV infection), and in outpatient therapy failure. [3]

Most patients with pneumococcal pneumonia have significant leukocytosis (>12,000 cells/μL), and up to one fourth have a hemoglobin level of 10 mg/dL or less.

A small study by Casado Flores et al evaluated a rapid immunochromatographic test for detection of the pneumococcal antigen, C polysaccharide antigen, in children with pleural effusion. [59] The positive predictive value was 96%, and the sensitivity and specificity were high. In this study, the immunochromatographic test made identification of the pneumococcal origin of effusion easy.

A urinary antigen test based on an immunochromatographic membrane technique is widely available to detect the C-polysaccharide antigen of S pneumoniae but does not distinguish between pneumococcal serotypes. In the diagnosis of S pneumoniae CAP, this test has a sensitivity of 77%-88% and a specificity of 67%-100%. [60, 61] However, the clinical usefulness of this pneumococcal urinary antigen test is not well defined. The 2019 IDSA CAP guidelines do not recommend routine urinary testing for pneumococcal antigen in adults with CAP, except in adults with severe pneumonia. [62]

Serotype-specific urinary antigen detection has been shown to substantially increase the detection of pneumococcal pneumonia among adults hospitalized with CAP; [63] however, these assays are not yet in routine use. The emergence of rapid low-cost genomic sequence detection assays have the potential of improving pathogen-directed therapy, thereby improving antimicrobial stewardship. [62]

A multiplex PCR panel is a novel tool that identifies common bacterial and viral pathogens seen in community- and hospital-acquired pneumonias. Although overidentification of colonizers is a potential limitation, this diagnostic study is a powerful tool for antibiotic stewardship that will permit rapid intervention and optimal targeted therapy. [64] PCR-based detection of S pneumoniae depends on the amplification of pneumococcus-specific genes. Some studies suggest that sputum PCR is a more sensitive method than sputum culture for detecting S pneumoniae in patients hospitalized with CAP, especially in those previously treated with antibiotics. [65]

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