A 42-year-old man is brought to the hospital by his wife due to headache and a change in mental status. His wife reports that the symptoms started yesterday and are getting worse. He has experienced migraines previously, but the pain and photophobia are much worse this time. He was not himself and was very confused this morning, so she brought him to the Emergency Department. His temperature is 38.8°C with a normal blood pressure and heart rate. There is moderate neck stiffness on examination with no focal neurologic deficits. A lumbar puncture is performed, and a Gram stain of the cerebrospinal fluid (CSF) shows gram-positive cocci.
What is the most likely pathogen, and what would be expected on CSF analysis? (Note: WBCs are white blood cells.)
: S. pneumoniae, ↑ WBCs, ↑ protein, ↓ glucose. The Gram stain confirms that this patient has acute bacterial meningitis, which commonly presents with fever, headache, neck stiffness, and/or mental status changes. Other symptoms include photosensitivity and seizures. The most common causative organism is S. pneumoniae, which is a lancet-shaped diplococcus. Other common pathogens that cause meningitis are summarized in Figure below.
The CSF findings in meningitis are high yield for the shelf examination. Bacterial meningitis will present with very elevated lymphocytes with a neutrophil predominance, low glucose, and elevated protein. Viral meningitis will present with elevated lymphocytes with a lymphocyte predominance (though there is often a neutrophil predominance early in the course of the infection), normal glucose, and mildly elevated protein. Fungal meningitis will have findings similar to viral meningitis, except that the glucose will be low. Meningitis due to tuberculosis (TB) will have findings similar to fungal meningitis, but other clues will be given to help make the diagnosis such as exposures, risk factors, and acid-fast bacilli (AFB) smear or culture.