Differential Diagnosis for Gram Neg Cocci in Pairs + Stiff Neck

• Single Most Likely Diagnosis

  • Neisseria meningitidis infection: This bacterium is known for causing meningitis, which presents with symptoms like stiff neck (nuchal rigidity), and it is a Gram-negative coccus that typically appears in pairs (diplococci). The combination of these characteristics makes it the most likely diagnosis.

• Other Likely Diagnoses

  • Moraxella catarrhalis infection: Although less commonly associated with meningitis, Moraxella catarrhalis is a Gram-negative coccus that can appear in pairs. It's more often linked to respiratory infections but can cause invasive disease in certain contexts.
  • Neisseria gonorrhoeae infection (disseminated): While primarily known for causing sexually transmitted infections, Neisseria gonorrhoeae can disseminate and cause infections in other parts of the body, including the central nervous system, though this is less common.

• Do Not Miss Diagnoses

  • Haemophilus influenzae type b (Hib) infection: Although Hib is a Gram-negative coccobacillus rather than a coccus, it's a critical cause of meningitis, especially in unvaccinated children. The presentation can be similar, and missing this diagnosis could be fatal.
  • Streptococcus pneumoniae infection: While S. pneumoniae is a Gram-positive coccus, it's a leading cause of bacterial meningitis. The clinical presentation of meningitis (including stiff neck) can be similar across different pathogens, making it crucial not to miss this diagnosis based on Gram stain appearance alone.

• Rare Diagnoses

  • Kingella kingae infection: This is a Gram-negative coccus that can cause invasive infections, including meningitis, particularly in young children. It's less common but should be considered in the appropriate clinical context.
  • Other rare Gram-negative cocci: There are other, less common Gram-negative cocci that could potentially cause infections presenting with stiff neck, such as certain species of Acinetobacter or Branhamella. However, these would be rare causes of meningitis or similar syndromes.