MKSAP Quiz: redness at the site of a mosquito bite
A 25-year-old woman is evaluated for redness that developed over her right leg at the site of a mosquito bite. She is otherwise healthy and takes no medications. Following a physical exam, what is the most appropriate empiric outpatient therapy?
A 25-year-old woman is evaluated for redness that developed over her right leg at the site of a mosquito bite. She is otherwise healthy and takes no medications.
On physical examination, temperature is 37.2 °C (99.0 °F), blood pressure is 120/70 mm Hg, pulse rate is 70/min, and respiration rate is 14/min. There is an erythematous 3 × 3-cm patch on the right thigh. The area is warm to the touch with no evidence of purulence, fluctuance, crepitus, or lymphadenopathy.
Which of the following is the most appropriate empiric outpatient therapy?
A. Cephalexin
B. Doxycycline
C. Fluconazole
D. Metronidazole
E. Trimethoprim-sulfamethoxazole
MKSAP Answer and Critique
The correct answer is A: Cephalexin. This item is available to MKSAP 16 subscribers as item 77 in the Infectious Disease section. More information is available online.
This patient has nonpurulent cellulitis that is most likely caused by β-hemolytic streptococci, and empiric outpatient treatment with a β-lactam agent such as cephalexin or dicloxacillin is recommended. Cellulitis is a bacterial skin infection involving the dermis and subcutaneous tissues. This infection is most frequently associated with dermatologic conditions involving breaks in the skin, such as eczema, tinea pedis, or chronic skin ulcers, and conditions leading to chronic lymphedema, such as mastectomy and lymph node dissections or saphenous vein grafts used in bypass surgery. Cellulitis should be suspected in patients with the acute onset of spreading erythema, edema, pain or tenderness, and warmth. Fever, although common, is not uniformly present. Patients with severe disease may have associated systemic toxicity. The most common pathogens are Staphylococcus aureus and the β-hemolytic streptococci, especially group A β-hemolytic streptococci (GABHS). GABHS is most often associated with nonpurulent cellulitis, whereas S. aureus may cause concomitant abscesses, furuncles, carbuncles, and bullous impetigo.
Doxycycline and trimethoprim-sulfamethoxazole have activity against community-associated methicillin-resistant S. aureus but are not reliably effective against β-hemolytic streptococci.
Fluconazole is an antifungal agent. Fungi do not usually cause cellulitis in young, healthy persons, but fungal infection should be considered in immunocompromised patients.
Metronidazole is an antimicrobial agent used to treat some anaerobic bacterial and protozoal infections. Although metronidazole is active against some microaerophilic bacteria, it is not effective for treatment of β-hemolytic streptococci.
Key Point
- Outpatients with nonpurulent cellulitis should be treated empirically with a β-lactam agent such as cephalexin or dicloxacillin that is active against β-hemolytic streptococci.