Mixed infection in adult bacterial meningitis

12 adult patients suffering from bacterial meningitis caused by mixed infection were identified at Kaohsiung Chang Gung Memorial Hospital over a period of 13 years (1986-1998), and they accounted for 6.5% (12/184) of our culture-proven adult bacterial meningitis. The 12 cases included seven males and five females, aged 17-74 years. Six of the 12 cases had community-acquired infections and the other six had nosocomially-acquired infections. Ten of the 12 cases had associated underlying diseases, with head trauma and/or neurosurgical procedure being the most frequent. Both gram-negative and gram-positive pathogens were identified in these 12 cases with gram-negative pathogens outnumbering the gram-positive ones. The implicated pathogens, starting with the most frequent, included Enterobacter species (Enterobacter cloacae, Enterobacter aerogenes), Klebsiella species (Klebsiella pneumoniae, Klebsiella oxytoca), Escherichia coli, Staphylococcus species (Staphylococcus aureus, Staphylococcus haemolyticus), Pseudomonas aeruginosa, Acinetobacter baumannii, Enterococcus, Serratia marcescens, Citrobacter diversus, Proteus mirabilis, Streptococcus viridans and Neisseria meningitidis. Six of the 12 cases were found to have multi-antibiotic-resistant strains, which included E. cloacae in one, A. baumannii in one, K. pneumoniae in one and S. aureus in three. The management of these 12 cases included appropriate antibiotics and neurosurgical procedures including shunt revision. Despite the complexity of implicated pathogens and the high incidence of emergence of resistant strains, the overall mortality rate (8.3%, 1/12) was not higher than that in adult bacterial meningitis. However, complete recuperation was difficult in adult patients with mixed bacterial meningitis.