Gonococcal septic arthritis is caused by which organism?

• A. Haemophilus influenzae
• B. Streptococcus pneumoniae
• C. Staphylococcus aureus
• D. Neisseria gonorrhoeae

Answer: (D)

Gonococcal septic arthritis is caused by Neisseria gonorrhoeae, a Gram-negative diplococcus that often leads to disseminated gonococcal infection in sexually active individuals. This organism targets mucosal surfaces (genital, rectal, pharyngeal) and can seed joints, producing arthritis that may be migratory with tenosynovitis and sometimes dermatitis. Diagnostically, you can find intracellular Gram-negative diplococci in purulent synovial fluid or detect the organism by nucleic acid amplification tests from mucosal sites; cultures are done on selective media such as Thayer-Martin. Other bacteria listed, like Staphylococcus aureus, Haemophilus influenzae, or Streptococcus pneumoniae, are not the causes of gonococcal septic arthritis, which is why Neisseria gonorrhoeae is the correct answer.