pediatrics
Bacterial Meningitis in Infants Over 3 Months of Age
Diagnosis of Bacterial Meningitis in Infants
Cerebrospinal fluid (CSF) analysis In general, Lumbar Puncture (Spinal Tap) should be done whenever the diagnosis of meningitis is known or suspected in an infant. However, lumbar puncture may be delayed for the following reasons: Clinically important cardiorespiratory compromise (most often in young infants) Signs of significantly increased intracranial pressure, including retinal changes; altered pupillary responses; hypertension, bradycardia, and respiratory depression (Cushing triad); and focal neurologic signs Suspected intracranial injury, including presence of visible injuries, particularly to the head, or history suggestive of nonaccidental injury Infection at the site of lumbar puncture Suspicion or history of bleeding disorders (eg, hemophilia, severe thrombocytopenia) In these circumstances, blood cultures should be done and antibiotics should be given empirically without doing the lumbar puncture. In cases of suspected increased intracranial pressure, arrangements should be made for a neuroimaging study (eg, cranial CT with and without contrast enhancement, cranial ultrasonography) during or immediately after antibiotics administration. If the results of the imaging study suggest it is safe, lumbar puncture may be done. However, it is not necessary to routinely do CT before lumbar puncture in young children with suspected meningitis; herniation of the brain is rare in young children with bacterial meningitis, even though all patients with meningitis have some degree of increased intracranial pressure. CSF is sent for analysis, typically cell count, protein, glucose, Gram stain, culture, and, in selected infants, polymerase chain reaction (PCR) tests for Overview of Enterovirus Infections (eg, in infants with meningitis during the late summer and autumn months in the US), Typical CSF findingsin bacterial meningitis include High white blood cell (WBC) count (> 500/mcL [0.5 × 109/L] often to as high as 10,000 WBC/mcL [10 × 109/L], with a predominance of polymorphonuclear leukocytes [> 80%]) Elevated protein (> 100 mg/dL [1 gm/L]) Low glucose (< 40 mg/dL [2.2 mmol/L], often < 10 mg/dL [0.56 mmol/L], and CSF:blood glucose ratio typically < 0.33) Gram stain often shows organisms in the CSF in bacterial meningitis. Although findings may vary somewhat, infants who have bacterial meningitis very rarely have completely normal CSF at examination. Infants also should have 2 sets of blood cultures (if possible; minimum 1 set of aerobic and anaerobic culture bottles), serum electrolytes, complete blood count and differential, and a urinalysis and urine culture. Symptoms and signs of bacterial meningitis may also be caused by other CNS infections, including Viral Meningitis (typically enteroviral or, in young infants, parechoviral), In these other causes of meningitis, CSF findings most often include < 500 WBC/mcL (0.5 × 109/L) with < 50% polymorphonuclear leukocytes, protein < 100 mg/dL (1 g/L), normal glucose, and a negative Gram stain for organisms. 