Clarifying one thing first

Step 1: Reassess with a focused history and exam

• Exposure history: travel, contaminated food/water, mosquito exposure (day-biting Aedes → dengue), rodent/animal contact, freshwater/flood exposure (leptospirosis), tick/mite bites or rural/grassy exposure (scrub typhus), sick contacts, sexual history, any rash.
• Exam: look specifically for rose spots (typhoid), eschar (scrub typhus - a classic diagnostic clue often missed), conjunctival suffusion and calf tenderness (leptospirosis), petechiae/tourniquet test (dengue), hepatosplenomegaly, lymphadenopathy, jaundice, meningismus, joint swelling.
• Red flags mandating hospitalization now: hypotension/tachycardia out of proportion to fever, bleeding manifestations, altered sensorium, oliguria/dark urine, severe abdominal pain or distension, breathlessness, jaundice - these suggest dengue hemorrhagic fever/shock, Weil's disease (severe leptospirosis), typhoid with perforation, or severe malaria.

Step 2: Basic diagnostic workup (should have been done before or at treatment failure)

• CBC with differential (leukopenia + relative bradycardia → typhoid; thrombocytopenia + leukopenia → dengue; leukocytosis → leptospirosis/bacterial)
• Peripheral smear (thick and thin) + rapid malaria antigen test, repeated over 2-3 samples if negative
• Blood culture (ideally before further antibiotics - this is the gold standard for enteric fever and also picks up other bacteremias)
• Dengue NS1 antigen (days 1-5) and IgM/IgG serology (after day 5)
• LFTs, RFTs, urinalysis (urine may show sterile pyuria/casts in leptospirosis)
• CRP/procalcitonin - helps separate bacterial (leptospirosis, typhoid) from viral causes
• Widal/Typhidot IgM has limited reliability alone; blood culture is preferred
• If endemic exposure fits: scrub typhus IgM ELISA/Weil-Felix, leptospirosis IgM/MAT
• Chest X-ray if respiratory symptoms

Step 3: Why azithromycin may have failed

• Wrong diagnosis - if this is dengue, chikungunya, or another viral illness, no antibiotic will help; supportive care and time are the treatment.
• Antibiotic resistance - azithromycin resistance in Salmonella Typhi is increasingly reported, particularly in South Asia, and extensively drug-resistant (XDR) strains resistant to azithromycin, fluoroquinolones, and third-generation cephalosporins have emerged in parts of the region (Goldman-Cecil Medicine; Harrison's Principles of Internal Medicine). If enteric fever is confirmed or strongly suspected and there's no response, IV ceftriaxone (or based on culture sensitivity) is the next empirical step rather than repeating or escalating azithromycin blindly.
• Wrong drug for the organism - if this turns out to be leptospirosis or scrub typhus, doxycycline is the preferred first-line agent (azithromycin is an alternative in leptospirosis, but doxycycline has better outcomes data for scrub typhus).
• Complication rather than treatment failure - by day 7-14 of untreated/inadequately treated typhoid, complications like intestinal perforation, hepatitis, or myocarditis can occur and need imaging/admission, not just a drug switch.

Practical next step

1. The focused exam above (looking specifically for eschar, rose spots, rash, hepatosplenomegaly)
2. The lab panel above - at minimum CBC, malaria smear/antigen, dengue NS1/serology, blood culture, LFT/RFT, urinalysis
3. Empirical step-up only guided by findings - e.g., IV ceftriaxone if enteric fever remains likely and cultures are pending/resistance suspected, doxycycline if scrub typhus/leptospirosis is likely, or purely supportive care with monitoring if dengue is confirmed (avoiding NSAIDs/aspirin because of bleeding risk).
4. Admission if any red flag above is present.