Risk factors for adult nosocomial meningitis after craniotomy: role of antibiotic prophylaxis.

OBJECTIVE: To evaluate incidence and risk factors of postoperative meningitis, with special emphasis on antibiotic prophylaxis, in a series of 6243 consecutive craniotomies.
METHODS: Meningitis was individualized from a prospective surveillance database of surgical site infections after craniotomy. Ventriculitis related to external ventricular drainage or cerebrospinal fluid shunt were excluded. From May 1997 until March 1999, no antibiotic prophylaxis was prescribed for scheduled, clean, lasting less than 4 hours craniotomies, whereas emergency, clean-contaminated, or long-lasting craniotomies received cloxacillin or amoxicillin-clavulanate. From April 1999 until December 2003, prophylaxis was given to every craniotomy. Independent risk factors for meningitis were studied by a multivariate analysis. Efficacy of antibiotic prophylaxis in preventing meningitis was studied as well as consequences on bacterial flora.
RESULTS: The overall meningitis rate was 1.52%. Independent risk factors were cerebrospinal fluid leakage, concomitant incision infection, male sex, and surgical duration. Antibiotic prophylaxis reduced incision infections from 8.8% down to 4.6% (P < 0.0001) but did not prevent meningitis: 1.63% in patients without antibiotic prophylaxis and 1.50% in those who received prophylaxis. Bacteria responsible for meningitis were mainly noncutaneous in patients receiving antibiotics and cutaneous in patients without prophylaxis. In the former, microorganisms tended to be less susceptible to the prophylactic antibiotics administered. Mortality rate was higher in meningitis caused by noncutaneous bacteria as compared with those caused by cutaneous microorganisms.
CONCLUSION: Perioperative antibiotic prophylaxis, although clearly effective for the prevention of incision infections, does not prevent meningitis and tends to select prophylaxis resistant microorganisms.