What's the next step in managing a 25-year-old army recruit with a 2-week history of dry cough, diarrhea, and polyuria, who had partial relief with Z-pack (azithromycin) and has lost 8 pounds, with normal chest X-ray (CXR), complete blood count (CBC), comprehensive metabolic panel (CMP), urinalysis (UA), and serum osmolality (SOSM)?

Evaluation and Management of Persistent Dry Cough with Systemic Symptoms in a Young Adult

Testing for tuberculosis is the next appropriate step in managing this 25-year-old army recruit with persistent dry cough, diarrhea, polyuria, and weight loss despite partial response to azithromycin.

Clinical Presentation Analysis

The patient presents with a constellation of concerning symptoms:

• Persistent dry cough for 2 weeks
• Diarrhea
• Polyuria
• 8-pound weight loss
• Only partial response to azithromycin (Z-pack)
• Normal initial workup (CXR, CBC, CMP, UA, serum osmolality)

This presentation suggests a systemic infectious process that has not been fully addressed by the initial antibiotic treatment and requires further investigation.

Diagnostic Considerations

1. Tuberculosis Evaluation

• Military recruits are at higher risk for TB due to congregate living conditions
• The combination of persistent cough, weight loss, and systemic symptoms despite partial treatment with azithromycin strongly suggests possible tuberculosis
• TB testing should include:
  • Interferon-gamma release assay (IGRA) or tuberculin skin test (TST)
  • If positive, follow with sputum AFB smear and culture
  • Consider chest CT if CXR is normal but suspicion remains high

2. Gastrointestinal Pathogen Evaluation

• The combination of diarrhea and respiratory symptoms suggests possible enteric infection with systemic manifestations
• Azithromycin provides only partial coverage for some gastrointestinal pathogens 1
• Consider stool studies:
  • Stool culture for bacterial pathogens
  • Ova and parasite examination
  • Giardia and Cryptosporidium antigen testing
  • C. difficile testing if recent antibiotic exposure

3. Polyuria Evaluation

• Despite normal UA and serum osmolality, the polyuria warrants further investigation
• Consider:
  • 24-hour urine collection for volume, osmolality, and electrolytes
  • Water deprivation test if diabetes insipidus is suspected

Management Algorithm

1. Immediate Testing:

   • TB testing (IGRA or TST)
   • Comprehensive stool studies
   • HIV testing (given the constellation of symptoms)

2. If TB testing is positive:

   • Initiate respiratory isolation
   • Obtain sputum samples for AFB smear and culture
   • Chest CT if CXR is normal
   • Consult infectious disease specialist

3. If stool studies identify a pathogen:

   • Target therapy based on identified organism
   • For bacterial pathogens with partial azithromycin response, consider:
     • Complete course of azithromycin if sensitive (500mg daily for 3 days) 1, 2
     • Alternative antibiotic based on susceptibility testing

4. If initial testing is negative:

   • Consider bronchoscopy with bronchoalveolar lavage
   • Evaluate for non-infectious causes:
     • Sarcoidosis
     • Chronic fatigue syndrome 3
     • Autoimmune disorders

Rationale for TB Testing as Next Step

The presentation strongly suggests tuberculosis for several reasons:

1. Military recruits have higher TB risk due to congregate living
2. The combination of dry cough, weight loss, and systemic symptoms is classic for TB
3. Normal CXR does not rule out early TB
4. Partial response to azithromycin is consistent with TB (which would not respond fully to this antibiotic)

Important Considerations

• Azithromycin efficacy: While azithromycin is effective for many respiratory and gastrointestinal infections 4, 1, the partial response suggests either resistant organisms or a pathogen not covered by this antibiotic
• Military setting: Consider endemic infections common in military settings or specific deployment locations
• Weight loss: The 8-pound weight loss is significant and suggests a more serious underlying condition than a simple respiratory infection
• Normal initial workup: Many serious infections can present with initially normal laboratory studies and imaging

By prioritizing TB testing while simultaneously investigating gastrointestinal pathogens, you can efficiently identify the underlying cause of this concerning constellation of symptoms and initiate appropriate treatment.