A previously healthy 32-year-old woman comes to the doctor because of a 2-day history of fever and an area of swelling and redness on her right forearm. Six hours ago, she noticed red streaks extending from her forearm to her elbow. She has not traveled, and there is no history of trauma. Her temperature is 37.8°C. Epitrochlear lymph nodes are enlarged. Examination of the distal radial aspect of the right upper extremity shows an 8 x 13 cm warm, erythematous area of edema that is tender to palpation; there is a warm, tender red streak extending from this area to the elbow.

What is the most likely causal organism?

1) Haemophilus influenzae
2) Beta-hemolytic streptococcus
3) Pseudomonas aeruginosa
4) Salmonella choleraesuis
5) Staphylococcus epidermidis

The 32-year-old woman with fever, swelling, redness, and lymph node enlargement likely has cellulitis caused by beta-hemolytic streptococcus, specifically Streptococcus pyogenes. So the correct answer is B

Explanation:

The clinical presentation of a previously healthy 32-year-old woman with fever, swelling and redness on her forearm, red streaks extending to her elbow, enlarged epitrochlear lymph nodes, and warm, erythematous area of edema suggests a bacterial infection.

The condition described is consistent with cellulitis, which is often caused by beta-hemolytic streptococcus, specifically Streptococcus pyogenes. This organism is known for its ability to cause various skin infections, including cellulitis and erysipelas, by breaching the epidermis through a cut or abrasion.

The most likely causal organism for the condition described is beta-hemolytic streptococcus.