Figure 147.1 Gram-stained sputum specimen positive for S. pneumoniae demonstrates lancet-shaped gram-positive diplococci.
The BinaxNOW® test involves dipping a special swab into a urine specimen, or a pleural fluid specimen, at room temperature and applying the swab to an immunochromatographic membrane in a booklet-like device that is closed after the swab is set up. A positive test result, which must be read 15 minutes later, appears as a pink-to-purple colored line in a window on the cover of the booklet. Importantly, isolation of the pneumococcal organism is still necessary to assess susceptibility to penicillin and other antibiotics.
Meningitis
A specific diagnosis of pneumococcal meningitis can be confirmed quickly during the initial examination of the patient by identification of the organism on a Gram stain of CSF or by detection of pneumococcal C-polysaccharide cell wall antigen in a CSF specimen using the immunochromatographic membrane assay. The test is performed and read in the same manner as described above for testing a urine specimen. However, in patients with pneumococcal meningitis, the test shows a very high sensitivity (100% or nearly so) and very high specificity (100% or nearly so) in both children and adults. The availability of rapid diagnostic tests for the diagnosis of S. pneumoniae meningitis facilitates prompt initiation of appropriate antibiotic therapy while waiting for the results of the culture of CSF.
Antibiotic susceptibility testing
The spectrum of antibiotic minimum inhibitory concentrations (MICs) of S. pneumoniae strains is routinely determined employing automated procedures against a panel of antibiotics specified by the Clinical and Laboratory Standards Institute (CLSI, Wayne, PA). The panel of antibiotics includes penicillin, cefaclor, cefuroxime, cefotaxime, ceftriaxone, cefepime, meropenem, levofloxacin, azithromycin, erythromycin, tetracycline, chloramphenicol, clindamycin, amoxicillin-clavulanate, trimethoprim–sulfamethoxazole, and vancomycin. MIC breakpoints for non-meningitis and meningitis isolates to selected antibiotics are included in the footnotes of Tables 147.1 and 147.2, respectively.
| Clinical assessment of pneumonia | Recommended antibioticsa | Recommended antibiotic dosagesa |
|---|---|---|
| Ambulatory adult without any comorbidity or recent antibiotic treatment | First choice: a macrolide, either azithromycin or clarithromycin or erythromycin | Azithromycin 500 mg on d 1 and then 250 mg PO for 4 d; or clarithromycin 500 mg PO q12h for 7–14 days; or erythromycin 500 mg PO q12h for 7–14 d |
| Alternate choice: doxcycline | Doxycycline 100 mg PO q12h for 7–14 d | |
| Ambulatory adult 50 years of age and older with one or more comorbid condition and/or recent antibiotic treatment | First choice: a fluoroquinolone with antipneumococcal activity. | Levofloxacin, 750 mg PO q24h for 5 d; gatifloxacin, 400 mg PO q24h for 7–14 d; moxifloxacin, 400 mg PO q24h for 7–14 d; or gemifloxacin, 320 mg PO q24h for 7 d |
| Alternate choice: amoxicillin–clavulanate or amoxicillin or cefuroxime plus a macrolide | Amoxicillin–clavulanate 875 mg/125 mg PO q12h for 7–14 d; amoxicillin 875 mg PO q12h for 7–14 d; or cefuroxime axetil 500 mg PO q12h for 7–14 d, plus azithromycin or clarithromycin as described above | |
| Hospitalized adult with or without either comorbid conditions or recent antibiotic treatment | First choice: a fluoroquinolone with antipneumococcal activity | Levofloxacin, 750 mg PO q24h for 5 d; gatifloxacin, 400 mg PO q24h for 7–14 d; moxifloxacin, 400 mg PO q24h for 7–14 d; or gemifloxacin, 320 mg PO q24h for 7 d |
| Alternate choice: ceftriaxone or cefotaxime plus a macrolide | Ceftriaxone, 1–2 g IV/IM q24h for 7–14 d; or cefotaxime, 1–2 g IV q8h for 7–14 d; plus Azithromycin, 500 mg IV, then PO, q24h for 7–10 d; or clarithromycin 500 mg PO q12h for 7–14 d |
a Streptococcus pneumoniae isolated from blood or pleural fluid must be tested for antibiotic susceptibility and choice of antibiotic treatment should be based on these results. For these S. pneumoniae isolates (non-meningitis isolates), the MIC breakpoints in µg/mL of penicillin parenterally administered susceptible ≤2, intermediate = 4, and resistant ≥8; ceftriaxone susceptible ≤1, intermediate = 2, and resistant ≥4; cefotaxime susceptible ≤1, intermediate = 2, and resistant ≥4; azithromycin susceptible ≤0.5, intermediate = 1, and resistant ≥2; levofloxacin susceptible ≤2, intermediate = 4, and resistant ≥8. The antibiotic regimen selected should exceed these MICs.
| Penicillin allergy | Age group | Recommendations for antibiotics | Recommendations for dosage of antibioticsa |
|---|---|---|---|
| No | Child | Ceftriaxone or cefotaxime plus vancomycin | Ceftriaxone, 50 mg/kg IV q12h, or cefotaximea, 50 mg/kg IV q6h plus vancomycin, 10–15 mg/kg IV q6h (or q12h if 12–16 yr), 10–14 d plus dexamethasone 0.15 mg/kg IV q6h for 2–4 d, starting 10–20 minutes before first dose of antibioticsb |
| Adult | Ceftriaxone or cefotaxime plus vancomycin plus dexamethasone, maybe plus rifampin | Ceftriaxone, 2 g IV q12h, or cefotaxime, 2 g IV q4h plus vancomycin, 1 g IV q12h, 10–14 d plus dexamethasone 0.15 mg/kg IV q6h for 2–4 d, 10–20 minutes before antibiotics, maybe plus rifampin, 300 mg PO q12h for 10–14 d | |
| Yes | Child | Chloramphenicol plus vancomycin plus dexamethasone | Chloramphenicol, 75–100 mg/kg IV q6h plus vancomycin 10–15 mg/kg IV q6h (or q12h if 12–16 yr), 10–14 d plus dexamethasone 0.15 mg/kg IV q6h for 2–4 d, starting 10–20 minutes before first dose of antibioticsb |
| Adult | Chloramphenicol plus vancomycin plus dexamethasone, maybe plus rifampin | Chloramphenicol, 1500 mg IV q6h plus vancomycin, 1 g IV q12h, 10–14 d plus dexamethasone 0.15 mg/kg IV q6h for 2–4 d, 10–20 minutes before antibiotics, maybe plus rifampin, 300 mg PO q12h for 10–14 d |
a Streptococcus pneumoniae isolates recovered from cerebrospinal fluid (CSF) must be tested for antibiotic susceptibility and an antibiotic treatment regimen should be selected based on these results. For these CSF S. pneumoniae isolates, the MIC breakpoints in µg/mL of penicillin parenterally administered susceptible ≤0.06 and resistant ≥0.12; ceftriaxone susceptible ≤1, intermediate = 2, and resistant ≥4; cefotaxime susceptible ≤1, intermediate = 2, and resistant ≥4; vancomycin susceptible ≤1; chloramphenicol susceptible ≤4 and resistant ≥8. The antibiotic regimen selected should exceed these MICs. S. pneumoniae CSF isolates respond to ceftriaxone and cefotaxime because these third-generation cephalosporins achieve levels in the CSF above the MIC of most of these strains.
b Adjunctive dexamethasone, 0.15 mg/kg, every 6 hours for 2–4 days, in children residing in high-income countries (not low-income countries), preferably started 10–20 minutes before antibiotic therapy is begun, shows a decrease in any hearing loss and short-term neurologic sequelae, modest diminution of severity of illness, and slightly lowered case-fatality rate.
Although automated procedures have eclipsed other means of MIC determination, the MIC of an individual isolate of S. pneumoniae can be determined employing the E-test (AB Biodisk, Solna, Sweden). In this test, a penicillin-impregnated plastic-coated paper strip is placed on a blood agar plate inoculated with the isolate to produce a semiconfluent growth and incubated for 24 hours in a 5% CO2 atmosphere. The MIC represents the point of intersection of the strip by the ellipsoid zone of inhibition.
Infections due to the pneumococcus
Pneumonia
Importance
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