A 29-year-old man is evaluated for a 2-day history of diarrhea and crampy abdominal pain. Medical history is significant for non-Hodgkin lymphoma. Medications are rituximab, cyclophosphamide, doxorubicin hydrochloride, vincristine, and prednisone.
On physical examination, temperature is 38 °C (100.4 °F); other vital signs are normal. The abdomen is nondistended, bowel sounds are present, and mild tenderness to palpation is elicited.
A complete blood count and metabolic panel are normal. Rapid molecular gastrointestinal assay of the stool identifies Campylobacter.
Which of the following is the most appropriate empiric treatment for this patient?
MKSAP Answer and Critique
The correct answer is B. Azithromycin. This content is available to MKSAP 19 subscribers as Question 57 in the Infectious Disease section. More information about MKSAP is available online.
This patient, who is immunocompromised and has diarrhea caused by Campylobacter, a microaerophilic gram-negative bacilli, should receive empiric azithromycin therapy (Option B). Campylobacter-associated infection is usually foodborne, often following consumption of inadequately cooked poultry. The incubation period is about 3 days, and symptoms typically include diarrhea (visibly bloody in approximately 15% of patients), crampy abdominal pain, and fever. Stool culture and molecular testing can be used for diagnosis, although culture is needed to determine the antibiotic susceptibilities of the organism. Diarrhea usually resolves spontaneously without antibiotics. However, patients who have severe disease (bloody stools, bacteremia, high fever, or prolonged [>1 week] symptoms) or are at risk for severe disease, including immunocompromised persons, pregnant patients, or older adults, should receive antibiotic therapy. When indicated, macrolide therapy with azithromycin is preferred empirically because of increasing fluoroquinolone resistance, particularly in certain geographic locations, including Southeast Asia. Drugs that are usually active against Campylobacter include aminoglycosides and carbapenems; trimethoprim-sulfamethoxazole and tetracyclines may potentially be effective also. Treatment duration with azithromycin is typically 3 days, but a longer course may be indicated in immunocompromised persons. Other gastrointestinal illnesses that can potentially be treated with azithromycin include travelers' diarrhea or diarrhea caused by Vibrio cholerae, Salmonella, or Shigella.
Campylobacter exhibits high rates of resistance against amoxicillin (Option A), making it a less ideal empiric antibiotic choice. Amoxicillin can be used to treat Salmonella infection or as part of combination therapy against the peptic ulcer disease–associated pathogen Helicobacter pylori.
Fidaxomicin (Option C), a novel macrocyclic antibiotic that inhibits RNA polymerase, is approved for treatment of Clostridioides difficile infection but has little to no activity against enteric gram-negative bacteria like Campylobacter.
Although metronidazole (Option D) has activity against some gastrointestinal pathogens, including Entamoeba, Giardia, H. pylori, and C. difficile, it is not reliably effective against Campylobacter and would not be considered for empiric therapy.
Campylobacter is inherently resistant to vancomycin (Option E), so this agent would not be considered for treatment of infection by this organism. Oral vancomycin is approved to treat C. difficile infection.
- Diarrhea caused by Campylobacter usually resolves spontaneously.
- Patients who have severe Campylobacter-related diarrhea (bloody stools, bacteremia, high fever, or prolonged [>1 week] symptoms) or are at risk for severe disease (immunocompromised persons, pregnant patients, or older adults) should receive azithromycin treatment or prophylaxis.