A 56-year-old female with rheumatoid arthritis on methotrexate is admitted to ICU with fever and acute confusional state following a brief diarrhoeal illness. On examination, her temperature is 38.6°C with neck stiffness and a Glasgow Coma Score of E3M5V4. Twenty-four hours later, her blood cultures grow gram positive bacilli.
a) What is the most likely diagnosis? (10% marks)
b) What is the most appropriate anti-microbial therapy? (15% marks)
21.2 1. Listeria Monocytogenes meningitis
2. IV Benzyl Penicillin 2.4g 4-hrly or IV Bactrim 160/800mg 6-hrly (penicillin-allergy)
Fever, confusion and diarrhoea? Neck stiffness?? In an immunocompromised person with faulty B-cells? The differentials are broad, but the college gives you a positive blood culture, and the answer practically throws itself at you. There are only a small range of Gram-positive bacilli which are common human pathogens:
- Bacillus anthracis
- Corynebacterium diphtheriae
- Nocardia asteroides
- Listeria monocytogenes
- Clostridium sp.
Of these, Nocardia and Listeria are the only ones which are likely to cause meningitis. Both are a likely candidate in a patient with poor humoural immunity, but the only one with the diarrhoeal illness as a prodrome is Listeria (Nocardia generally causes a respiratory illness before it invades the brain).
Ergo, the most appropriate antibiotic choice (via eTG) is benzylpenicillin, or Bactrim if there is a penicillin allergy.