Chapter 128. Pneumococcal Infections (Part 5)

Diagnostic Microbiology In patients with community-acquired pneumonia, a pneumococcal etiology is strongly suggested by the microscopic demonstration of large numbers of PMNs and slightly elongated gram-positive cocci in pairs and chains in the sputum. A sample such as the one shown in Fig. 128-2 is highly specific for pneumococcal infection of the lower airways. In the absence of such microscopic findings, the identification of pneumococci by culture is less specific, possibly reflecting colonization of the upper airways. Prior treatment with antibiotics can rapidly clear pneumococci from sputum. These factors need to be considered when sputum cultures from patients who...
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Chapter 128. Pneumococcal Infections (Part 5) Chapter 128. Pneumococcal Infections (Part 5) Diagnostic Microbiology In patients with community-acquired pneumonia, a pneumococcal etiologyis strongly suggested by the microscopic demonstration of large numbers of PMNsand slightly elongated gram-positive cocci in pairs and chains in the sputum. Asample such as the one shown in Fig. 128-2 is highly specific for pneumococcalinfection of the lower airways. In the absence of such microscopic findings, theidentification of pneumococci by culture is less specific, possibly reflectingcolonization of the upper airways. Prior treatment with antibiotics can rapidlyclear pneumococci from sputum. These factors need to be considered whensputum cultures from patients who appear to have pneumococcal pneumonia aresaid to yield only normal mouth flora and when the medical literature describeswhat appear to be poor results of sputum culture. A study of sputum Grams stainand culture in patients with proven (bacteremic) pneumococcal pneumoniashowed that about half of patients could not provide a sputum sample, provided asample of poor quality, or had received antibiotics for >18 h; results in theremaining cases showed >80% sensitivity of microscopic examination of a Gram-stained sputum sample and 90% sensitivity of a sputum culture. Blood culturesyield S. pneumoniae in ~25% of patients hospitalized for pneumococcalpneumonia. Figure 128-2 Gram-stained sputum from a patient with pneumococcal pneumoniashows polymorphonuclear cells with no epithelial cells, indicating the origin ofthe sample in inflammatory exudate without contamination by saliva. Slightlypleomorphic gram-positive coccobacilli appear, generally in pairs. Displacementof stained proteinaceous background material outlines a capsule surrounding someof the organisms. When obtained from a patient with pneumonia, a sample likethis one is highly specific in identifying the pneumococcus as the etiologic agent. Complications Empyema is the most common complication of pneumococcal pneumonia,occurring in ~2% of cases. Some fluid appears in the pleural space in a substantialproportion of cases of pneumococcal pneumonia, but this parapneumonic effusionusually reflects an inflammatory response to infection that has been containedwithin the lung, and its presence is self-limited. When bacteria reach the pleuralspace—either hematogenously or as a result of contiguous spread, possibly acrosslymphatics of the visceral pleura—empyema results. The finding of frank pus,bacteria (by microscopic examination), or fluid with a pH of ≤7.1 indicates theneed for aggressive and complete drainage, preferably by prompt insertion of achest tube, with verification by CT that fluid has been removed. Failure to drainmost or all of the fluid indicates the need for additional treatment, includingplacement of other tube(s) (thoracostomy) or thoracotomy. Empyema is likely iffluid is present and fever and leukocytosis (even low-grade) persist after 4–5 daysof appropriate antibiotic treatment for pneumococcal pneumonia. At this stage,thoracotomy is often needed for cure. Aggressive drainage is likely to reducemorbidity and mortality from empyema (Chap. 257). Meningitis Except during outbreaks of meningococcal infection, S. pneumoniae is themost common cause of bacterial meningitis in adults. Because of the remarkablesuccess of H. influenzae type b vaccine, S. pneumoniae now predominates amongcases in infants and toddlers as well (but not among those in newborns);nevertheless, the incidence of pneumococcal meningitis among children has beendramatically reduced by use of the pediatric pneumococcal conjugate vaccine (seePrevention, below). No distinctive clinical or laboratory features differentiate pneumococcalmeningitis from other bacterial meningitides. Patients note the sudden onset offever, headache, and stiffness or pain in the neck. Without treatment, there is aprogression over 24–48 h to confusion and then obtundation. On physicalexamination, the patient looks acutely ill and has a rigid neck. In such cases,lumbar puncture should not be delayed for CT of the head unless papilledema orfocal neurologic signs are evident. Typical findings in cerebrospinal fluid (CSF)consist of an increased WBC count (500–10,000 cells/μL) with ≥85% PMNs, anelevated protein level (100–500 mg/dL), and a decreased glucose level ( The appearance of pneumococcal infection at other, ordinarily sterile bodysites indicates hematogenous spread, usually during frank pneumonia or, in asmall proportion of cases, from an inapparent focus of infection. A case ofpneumococcal endocarditis is seen every few years at large tertiary-care hospitals.Purulent ...