eMedicine Specialties > Infectious Diseases > Lower Respiratory Tract Infections
Pneumococcal Infections: Differential Diagnoses & Workup
Updated: May 16, 2008
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
Workup
Laboratory Studies
- In any patient in whom a pneumococcal infection is suspected, Gram stain and culture should be performed using appropriate specimens, when possible, including one or more of the following:
- Blood
- Cerebrospinal fluid (CSF)
- Sputum
- Pleural fluid or lung aspirate
- Joint fluid
- Bone
- Other abscess or tissue specimens
- Specimens should be obtained prior to the initiation of antibiotic therapy and inoculated directly into blood-culture bottles, when possible.
- Antibiotic susceptibilities should be obtained on all cultures with growth of S pneumoniae.
- Other laboratory values that may be helpful in diagnosis and treatment include a complete blood cell (CBC) count and differential, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP).
- Conjunctivitis, otitis media, sinusitis: Laboratory work is not usually obtained in patients with conjunctivitis, otitis media, or sinusitis unless they have unusually high fevers or have an extremely ill appearance. If specimens are obtained, they should be sent for Gram stain and culture and susceptibility. In these cases, isolation of S pneumoniae should be considered a strong indication for pathogenicity and treatment.
- Pneumonia
- Many patients with pneumonia are treated presumptively with antibiotics to include coverage of S pneumoniae. When possible, sputum cultures should be obtained in patients with pneumonia. This can be accomplished via expectoration (in adults), collection of endotracheal specimens, or bronchoalveolar lavage (BAL).
- 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 provides good evidence for pneumococcus.
- When large effusions or empyema is present, attempts should be made to obtain pleural fluid for Gram stain and culture.
- Blood cultures should be obtained in hospitalized patients with pneumonia; in pneumococcal pneumonia, blood cultures are positive in an estimated 10% of children and up to 25% of adults.
- 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.
- Neutrophil levels, CRP levels, and ESR are all often elevated.
- In most patients with invasive pneumococcal infections, the WBC count is elevated (>12,000 cells/μL) and there is a predominance of neutrophils. However, the WBC count may be normal, especially early in the disease process. An abnormally low WBC count may indicate severe disease and a poor prognosis.
- The ESR and CRP level are typically elevated in patients with invasive pneumococcal disease.
- The development of a polymerase chain reaction (PCR) assay for S pneumoniae with sufficient sensitivity and specificity is underway.
- Meningitis
- CSF findings are typical of those found in bacterial meningitis and usually include the following:
- Elevated opening pressure
- Elevated WBC count (1000-5000 cells/μL) and elevated neutrophil level (>80%)
- Elevated protein level (>100 mg/dL)
- Decreased glucose level (<40 mg/dL; <50% of simultaneous blood glucose)
- Positive Gram stain and culture results in most patients with pneumococcal meningitis who did not receive antibiotics in the 4-6 hours prior to lumbar puncture.
- Rapid antigen tests (latex agglutination or enzyme immunosorbent assays) can be performed on CSF (as well as sputum and urine) but rarely provide information beyond what is obtained with Gram stain and culture. CSF obtained from patients pretreated with antibiotics may be an exception.
- Blood culture results are positive in up to 90% of patients.
- CSF findings are typical of those found in bacterial meningitis and usually include the following:
- Bacteremia: The WBC count may be elevated and blood cultures are positive for growth of S pneumoniae.
- Other invasive infections
- The WBC count, neutrophil level, CRP level, and ESR are often elevated in patients with bone, joint, soft tissue, cardiac, and other invasive infections.
- Specimens of appropriate material may yield positive Gram stain findings and/or culture growth.
- Blood cultures are frequently positive and should be obtained when possible.
- In females with peritonitis, vaginal swab cultures should be obtained in addition to blood and peritoneal cultures.
- Antimicrobial susceptibility testing should be performed on all isolates of S pneumoniae, regardless of the isolation site, because of the increasing prevalence of intermediately susceptible and resistant isolates.
- Microbiological laboratories should follow established guidelines regarding inoculum size and media (Mueller-Hinton agar with sheep, horse, or lysed horse red blood cells).
- Susceptibilities can be determined using the minimal inhibitory concentration (MIC) or using disk diffusion techniques, such as the E-test.
- The National Committee for Clinical Laboratory Standards (NCCLS) has defined S pneumoniae susceptibility as follows:
- Penicillin
- Susceptible: MIC is less than or equal to 0.06 µg/mL.
- Intermediate: MIC is between 0.12 and 1 µg/mL.
- Resistant: MIC is greater than or equal to 2 µg/mL.
- Cefotaxime/ceftriaxone
- Susceptible (non-CNS/CNS): MIC is less than or equal to 1 or 0.5 µg/mL, respectively.
- Intermediate (non-CNS/CNS): MIC is 2 or 1 µg/mL, respectively.
- Resistant (non-CNS/CNS): MIC is greater than or equal to 4 or 2 µg/mL, respectively.
- Penicillin
- Strains with intermediate or resistant susceptibility patterns should be considered nonsusceptible and alternate therapy used.
Imaging Studies
- Chest radiography
- Chest radiography should be performed in most patients with evidence of invasive pneumococcal infection and those with pneumonia.
- Early in the disease process, the chest radiography findings may appear normal
- The typical chest radiography finding in adolescents and adults with pneumococcal pneumonia is lobar consolidation.
- Infants and young children with pneumococcal pneumonia more often have a pattern of scattered parenchymal consolidation and bronchopneumonia.
- Other chest radiography findings may include air bronchograms, pleural effusions, pneumatoceles, and, rarely, abscesses.
- Cavitation is not a feature of S pneumoniae pneumonia and should prompt investigation for other pathogens.
- Ultrasonography/CT scanning
- Chest ultrasonography or chest CT scanning may be obtained to provide information on the presence and/or extent of pleural effusion/empyema and parenchymal disease.
- Sinus CT scanning may provide information about the presence and extent of sinus disease. Positive findings include opacification and/or air-fluid levels.
- Facial CT scanning should be obtained in patients with periorbital or orbital cellulitis to look for evidence of soft tissue swelling, bony involvement, cranial nerve impingement, or proptosis.
- MRI/CT scanning
- MRI or CT scanning of affected bones or joints should be obtained to observe for evidence of joint destruction, periosteal elevation, or a mass.
- An MRI of the brain may be obtained in patients with meningitis to determine the location and extent of infection involvement.
Other Tests
Echocardiography should be performed in patients in whom endocarditis is suspected.
Procedures
- Middle ear fluid aspiration
- Pleural fluid aspiration
- Chest tube thoracostomy or catheter placement
- Video-assisted thoracoscopy (VATS) or pleural decortication
- Lumbar puncture
- Joint fluid aspiration and/or wash-out of joint space
- Bone biopsy
- Soft tissue/muscle biopsy
Histologic Findings
See Causes.
More on Pneumococcal Infections |
| Overview: Pneumococcal Infections |
 Differential Diagnoses & Workup: Pneumococcal Infections |
| Treatment & Medication: Pneumococcal Infections |
| Follow-up: Pneumococcal Infections |
| Multimedia: Pneumococcal Infections |
| References |
| Further Reading |
| « Previous Page | Next Page » |
References
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Further Reading
For additional information, see Medscape's Pneumonia Resource Center, Otitis Media Resource Center, and Sepsis Resource Center.
Keywords
Streptococcus pneumoniae, S pneumoniae, pneumococcus , pneumococci, upper respiratory tract disease, lower respiratory tract disease, upper respiratory disease, lower respiratory disease, respiratory disease, community-acquired pneumonia, CAP, pneumonia, lung infection, respiratory infection, pneumococcal disease, otitis media, pharyngeal infection, nosocomial pneumonia, hospital-acquired pneumonia, bronchopneumonia, broncho-pneumonia, meningitis, tracheobronchitis, acute sinusitis, sinusitis, pneumococcal sepsis, pneumococcal pneumonia, pneumococcal conjunctivitis, pneumococcal otitis media, pneumococcal sinusitis, acute exacerbations of chronic bronchitis, AECB, pneumococcal meningitis, pneumococcal bacteremia, pneumococcal joint infection, pneumococcal bone infection, pneumococcal soft tissue infection, pneumococcal osteomyelitis, pneumococcal peritonitis, pneumococcal endocarditis, pneumococcal pericarditis, pneumococcal septic arthritis
