Question 21.2

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)

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College answer

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.