Meningitis in adults is primarily due to meningococci and pneumococci. The picture shows the value of reviewing the gram stain yourself and thus instituting appropriate antibiotic therapy. The gram stain shows the gram positive bacilli consistent with Listeria monocytogenes. Listeria is more likely in neonates, elderly, alcoholics, cancer patients, and immunosuppressed patients (ex. renal transplant patients). However, 30% of adult patients with documented L. monocytogenes meningitis have no apparent underlying condition. Serious Listeria infections have been associated with several foodborne outbreaks linked to contaminated cole slaw, milk and cheese.
Empirical antibiotic therapy should include coverage for the most likely cases in adults. This includes N. meningitidis or S. pneumoniae. However, gram negative organisms and possible Listeria. Thus, empirical coverage would include Ampicillin and Ceftriaxone. Given the CSF findings and the gram stain the appropriate antibiotic would be ampicillin or penicillin. There is an argument for in-vitro synergy with the addition of an aminoglycoside (2,3) but whether combination therapy has superior efficacy is unknown. An alternative choice is trimethoprim-sulfamethoxazole which is the only non beta-lactam agetn that is bactericidal in vitro (4).
In one large study involving patients 16 years and older from 1962-88, it was found that Streptococcus pneumoniae (37%), Neisseria meningitidis (13%) and Listeria monocytogenes (10%) were most commonly isolated pathogens (5). Only 67% of patients had the classic triad of fever, nuchal rigidity and mental status changes but all had at least one of these findings. 95% of patients had fever (T>100.0) with another 4% becoming febrile during the next 24 hours. Neck stiffness was present in 88% and 78% had a change in mental status (confused, lethargic, responsive to pain, unresponsive to stimuli) and 29% had new-onset seizures.
- Scheld WM. Chapter 374 - Bacterial meningitis and brain abscess. In Harrison's Principles of Internal Medicine, 13th Edition.pp.2296-2309.
Trautmann M, Wagner J, Chahin M, Weinke T. Listeria meningitis: report of ten recent cases and review of current therapeutic recommendations. J. Infect. 1985; 10: 107-14.
Hansen PB, Jensen TH, Lykkegaard S, Kristensen HS. Listeria monocytogenes meningitis in adults. Sixteen consecutive cases. 1973-1982. Scand J Infect Dis. 1987;19: 55-60.
Levitz RE, Quintiliani R. Trimethoprim-sulfamethoxazole for bacterial meningitis. Ann Intern Med 1984;100: 881-90.
Durand MI, Calderwood SB, Weber DJ, et al. Acute bacterial meningitis in adults: a review of 493 episodes. N Engl J Med 328(1): 21-28.