Chapter 128. Pneumococcal Infections (Part 5) pot

Pneumococcal Infections Part 5 Diagnostic Microbiology In patients with community-acquired pneumonia, a pneumococcal etiology is strongly suggested by the microscopic demonstration of

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 surrounding 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