Streptococcus pneumoniae

Streptococcus pneumoniae causes pneumococcal disease.

Epidemiology

Incidence – kills more people in the U.S. (40,000 annually) than any other vaccine-preventable disease
- Invasive pneumococcal disease – 22-25/100,000
Transmission – humans are the natural reservoir for S. pneumoniae; organism colonizes in nasopharynx
- Most common in winter and early spring

Organism

S. pneumoniae are gram-positive, typically lancet-shaped diplococci
More than 80 serotypes
S. pneumoniae serotypes that are pathogenic in humans are not always heavily encapsulated
- Virulence determined by composition of capsular polysaccharide
- Antibodies to capsular polysaccharides confer type-specific immunity

Risk for Invasive Disease

Asplenia
HIV infection
Alaska Native American Indian, African American
Immunocompromised patients

Clinical Presentation

Pneumonia
- S. pneumoniae is responsible for 50% of all cases of community-acquired pneumonia
  - Often develops as a secondary pneumonia during upper respiratory tract viral infections
  - Abrupt onset of fever, shaking chills, cough, dyspnea, tachypnea and fatigue
  - Bacteremia occurs in 25-40% of patients
    - S. pneumoniae causes 85% of all cases of bacteremia in pediatric population
    - Overall mortality rate for bacteremia is 20% but may reach 60% in elderly patients
Otitis media (OM)
- S. pneumoniae responsible for 30–50% of OM cases
  - ~90% of children in U.S. have at least one episode by age 3
  - 50% have >6 episodes/year
  - Penicillin-resistant pneumococcus is the most common cause of recurrent or persistent OM
Sinusitis
- S. pneumoniae responsible for up to 40% of nonviral sinusitis cases
Meningitis
- Neurologic sequelae common in survivors

Treatment

Often effectively treated with antibiotics
Complicating factors
- Delayed treatment
- Resistant bacteria
- Patient has another debilitating illness or is immunocompromised

Prevention

Current vaccines recommended by the CDC
- Adults – 23-valent polysaccharide vaccine (PPV23, Pneumovax™)
  - Pneumovax™ – serotypes included in the vaccine are 1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F, 33F
- Infants and toddlers – 7-valent polysaccharide conjugate vaccine (PCV7, Prevnar™)
  - Prevnar™ – serotypes included in the vaccine are 4,6B, 9V, 14,18C, 19F, 23F
- Clinical trials are in progress for 9 and 11 valent-conjugated vaccines that include serotypes 1 and 5, and serotypes 3 and 7F
- Vaccination pre- and post-titers may be used to assess immune response

Indications for Testing

Invasive disease (eg, pneumonia, meningitis)

Laboratory Testing

Initial testing – CBC, arterial blood gas, chemistry profile
Antigen-based testing
- Immunochromatographic urinary antigen testing in symptomatic adults has 70-80% sensitivity and >90% specificity
  - Most sensitive in presence of bacteremia
  - Prior antibiotic use does not affect antigen test
  - Urine antigen test may stay positive for up to one month; therefore, it is not useful for recurrences or to assess therapy
- Caution: children may asymptomatically shed S. pneumoniae antigen in urine, decreasing clinical specificity of assay
Culture is gold standard – blood, cerebrospinal fluid (CSF), respiratory sources
Nucleic amplification tests and PCR – still under investigation
Meningitis – Gram stain and CSF culture detect most cases of meningitis
Bacteremia and pneumonia
- Blood cultures are positive in a minority of cases of invasive disease
- High-quality sputum with gram stain and culture may also yield results
Other testing for community-acquired pneumonia may include Legionella and Mycoplasma

Differential Diagnosis

Asthma
Exacerbation of chronic obstructive pulmonary disease
Viral pneumonia
Fungal pneumonia
Pneumonitis

Tests generally appear in the order most useful for common clinical situations

Test name: CBC with Platelet Count & Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count with Flow Cell Differential

Use:

Initial testing for infectious process

Test name: Renal Function Panel

ARUP #: 0020144

Methodology: Refer to individual components

Use:

Test for renal function

Panel includes albumin, calcium, carbon dioxide, creatinine, chloride, glucose, phosphorous, potassium, sodium, and BUN

Test name: Streptococcus pneumoniae Antigen, Urine

ARUP #: 0060228

Methodology: Qualitative Immunochromatographic Assay

Use:

Rapid diagnostic test for invasive disease from S. pneumoniae (eg, bacteremia, pneumonia, meningitis)

Limitations:

False positives may occur because of cross-reactivity with other members of S. mitis group or asymptomatic colonization of S. pneumonia

Clinical correlation is recommended

Patients who have received the S. pneumoniae vaccines may test positive in the 48 hours following vaccination; avoid testing within 5 days of receiving vaccination

Test name: Streptococcus pneumoniae Antigen, CSF

ARUP #: 0061162

Methodology: Qualitative Immunochromatographic Assay

Use:

Diagnostic test for pneumonococcal meningitis

Limitations:

False positives may occur because of cross-reactivity with other members of S. mitis group

Clinical correlation is recommended

Patients who have received the S. pneumoniae vaccines may test positive in the 48 hours following vaccination; avoid testing within 5 days of receiving vaccination

Test name: Respiratory Culture (Includes Gram Stain 0060101)

ARUP #: 0060122

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Sinus swabs or aspirates should be ordered as a Wound Culture (0060132).

Use:

Determine presence of pneumonia

Test name: Blood Culture

ARUP #: 0060102

Methodology: Bactec® continuous monitoring system. Standard reference procedures for identification of aerobic and anaerobic microorganisms

Use:

Determine presence of pneumonia

Limitations:

Testing is limited to the University of Utah Health Sciences Center only

Test name: CSF Bacterial Culture (Includes Gram Stain 0060101)

ARUP #: 0060106

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification

Use:

Test for meningitis

Test name: Aerobic Organism Identification with Reflex to Susceptibility

ARUP #: 0065070

Methodology: Identification methods including Biochemical, MALDI TOF and/or 16S rDNA sequencing.

Use:

Gold standard for identification of S. pneumoniae

Limitations:

For suspected agents of bioterrorism, Salmonella or Shigella, notify your state department of health and refer isolates to your state laboratory for identification; susceptibilities on agents of bioterrorism are not performed at ARUP

Additional Tests Available

Test name: Streptococcus pneumoniae Antibodies, IgG (14 serotypes)

ARUP #: 0050725

Methodology: Quantitative Multi-Analyte Fluorescent Detection

Comments:

Quantify antibody levels to pneumococcal polysaccharides in persons receiving vaccine to determine response to vaccine and whether protective antibody levels are reached at 1 month post-immunization

Vaccination, pre- and post-antibody titer may aid in diagnosis of patients with suspected antibody deficiency with chronic/recurrent sinopulmonary infections

Test not designed to determine protection against S. pneumoniae based on a single sample

Test name: Legionella pneumophila Antigen, Urine

ARUP #: 0070322

Methodology: Qualitative Enzyme-Linked Immunosorbent Assay

Comments:

Test name: Mycoplasma pneumoniae by PCR

ARUP #: 0060256

Methodology: Qualitative Polymerase Chain Reaction

Comments: