Chapter 128. Pneumococcal Infections (Part 5) pot

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 appear to have pneumococcal pneumonia are said to yield only "normal mouth flora" and when the medical literature describes what appear to be poor results of sputum culture. A study of sputum Gram's stain and culture in patients with proven (bacteremic) pneumococcal pneumonia showed that about half of patients could not provide a sputum sample, provided a sample of poor quality, or had received antibiotics for >18 h; results in the remaining cases showed >80% sensitivity of microscopic examination of a Gram- stained sputum sample and 90% sensitivity of a sputum culture. Blood cultures yield S. pneumoniae in ~25% of patients hospitalized for pneumococcal pneumonia. Figure 128-2 Gram-stained sputum from a patient with pneumococcal pneumonia shows polymorphonuclear cells with no epithelial cells, indicating the origin of the sample in inflammatory exudate without contamination by saliva. Slightly pleomorphic gram- positive coccobacilli appear, generally in pairs. Displacement of stained proteinaceous background material outlines a capsule surroundin g some of the organisms. When obtained from a patient with pneumonia, a sample like this 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 substantial proportion of cases of pneumococcal pneumonia, but this parapneumonic effusion usually reflects an inflammatory response to infection that has been contained within the lung, and its presence is self-limited. When bacteria reach the pleural space—either hematogenously or as a result of contiguous spread, possibly across lymphatics of the visceral pleura—empyema results. The finding of frank pus, bacteria (by microscopic examination), or fluid with a pH of ≤7.1 indicates the need for aggressive and complete drainage, preferably by prompt insertion of a chest tube, with verification by CT that fluid has been removed. Failure to drain most or all of the fluid indicates the need for additional treatment, including placement of other tube(s) (thoracostomy) or thoracotomy. Empyema is likely if fluid is present and fever and leukocytosis (even low-grade) persist after 4–5 days of appropriate antibiotic treatment for pneumococcal pneumonia. At this stage, thoracotomy is often needed for cure. Aggressive drainage is likely to reduce morbidity and mortality from empyema (Chap. 257). Meningitis Except during outbreaks of meningococcal infection, S. pneumoniae is the most common cause of bacterial meningitis in adults. Because of the remarkable success of H. influenzae type b vaccine, S. pneumoniae now predominates among cases in infants and toddlers as well (but not among those in newborns); nevertheless, the incidence of pneumococcal meningitis among children has been dramatically reduced by use of the pediatric pneumococcal conjugate vaccine (see "Prevention," below). No distinctive clinical or laboratory features differentiate pneumococcal meningitis from other bacterial meningitides. Patients note the sudden onset of fever, headache, and stiffness or pain in the neck. Without treatment, there is a progression over 24–48 h to confusion and then obtundation. On physical examination, 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 or focal neurologic signs are evident. Typical findings in cerebrospinal fluid (CSF) consist of an increased WBC count (500–10,000 cells/μL) with ≥85% PMNs, an elevated protein level (100–500 mg/dL), and a decreased glucose level (<30 mg/dL). If antibiotics have not been given, large numbers of pneumococci are seen in Gram-stained CSF in virtually all cases, and specific therapy can be administered, although, because of its similar appearance, Listeria may be misidentified as the pneumococcus. If an effective antibiotic has already been given, the number of bacteria may be greatly decreased and microscopic examination of a Gram-stained specimen may yield negative results. In this situation, immunologic methods may detect pneumococcal capsule in the CSF in up to two-thirds of cases. Other Syndromes The appearance of pneumococcal infection at other, ordinarily sterile body sites indicates hematogenous spread, usually during frank pneumonia or, in a small proportion of cases, from an inapparent focus of infection. A case of pneumococcal endocarditis is seen every few years at large tertiary-care hospitals. Purulent pericarditis, occurring as a separate entity or together with endocarditis, is even rarer. The name Austrian's syndrome is given to the concurrence of pneumococcal pneumonia, endocarditis, and meningitis. Septic arthritis can arise spontaneously in a natural or prosthetic joint or as a complication of rheumatoid arthritis. Osteomyelitis in adults tends to involve vertebral bones. Pneumococcal peritonitis occurs by one of three pathogenetic pathways: (1) hematogenous spread when ascites or other preexisting peritoneal disease is present; (2) local spread from a perforated viscus (usually appendicitis or perforated ulcer); or (3) transit via the fallopian tubes. Salpingitis may be recognized with or without accompanying peritonitis. Epidural and brain abscesses arise as a complication of sinusitis or mastoiditis. Cellulitis is also uncommon, developing most often in persons who have connective tissue diseases or HIV infection. The appearance of any of these unusual pneumococcal infections may suggest that tests for HIV infection should be undertaken. Finally, for reasons that are unclear, unencapsulated (but not encapsulated) pneumococci may cause sporadic or epidemic conjunctivitis. . Chapter 128. Pneumococcal Infections (Part 5) Diagnostic Microbiology In patients with community-acquired pneumonia, a pneumococcal etiology is strongly. yield S. pneumoniae in ~25% of patients hospitalized for pneumococcal pneumonia. Figure 128- 2 Gram-stained sputum from a patient with pneumococcal pneumonia shows polymorphonuclear cells. 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