What is the likely diagnosis and management for an infant presenting with loose stools, elevated Total Leukocyte Count (TLC), and elevated Procalcitonin (PCT)?

Bacterial Gastroenteritis with Systemic Infection

An infant presenting with loose stools, elevated total leukocyte count (TLC), and elevated procalcitonin (PCT) most likely has bacterial gastroenteritis with systemic bacterial infection requiring immediate stool culture, blood culture, and empirical antibiotic therapy. 1

Diagnostic Reasoning

The combination of loose stools with elevated TLC and elevated PCT strongly suggests bacterial rather than viral etiology:

• Elevated PCT is highly specific for bacterial infection and indicates systemic bacterial involvement, as PCT rises early in bacterial infections and has higher diagnostic accuracy than CRP or WBC alone for identifying bacterial sepsis 1
• Bacterial gastroenteritis shares inflammatory features including fever, elevated white blood cell counts, and the presence of systemic markers of infection 1, 2
• PCT levels increase in bacterial infections with higher specificity than CRP for distinguishing bacterial from viral causes, making it a useful biomarker when blood culture results are not yet available 1

Immediate Diagnostic Workup

Obtain the following tests immediately:

• Stool culture to identify bacterial pathogens (Salmonella, Shigella, Campylobacter, enteropathogenic E. coli) 1
• Blood culture given the elevated PCT suggesting possible bacteremia 1
• Complete blood count with differential to further characterize the leukocytosis 1
• Serum electrolytes, BUN, and creatinine to assess hydration status and renal function 1
• Stool examination for blood and fecal leukocytes (though fecal leukocyte examination performs poorly to establish infectious cause, it may help differentiate inflammatory from secretory diarrhea) 1

Management Algorithm

Assess Hydration Status First

• Evaluate for signs of dehydration: skin turgor, mucous membrane moisture, mental status, capillary refill time, and vital signs 3, 4, 5
• Categorize dehydration severity: mild (3-5%), moderate (6-9%), or severe (≥10% fluid deficit) 3, 6
• Acute weight change is the most accurate assessment if premorbid weight is known 3

Fluid Resuscitation

• For mild to moderate dehydration: administer low-osmolarity oral rehydration solution (ORS) at 50-100 mL/kg over 2-4 hours 3, 6
• For severe dehydration (≥10% deficit): immediate intravenous isotonic fluids (lactated Ringer's or normal saline) at 20 mL/kg over 30 minutes 3, 6
• Replace ongoing losses: 10 mL/kg ORS for each watery stool and 2 mL/kg for each vomiting episode 6

Empirical Antibiotic Therapy

Start empirical antibiotics immediately while awaiting culture results given the elevated PCT and systemic signs of bacterial infection:

• For infants >6 months: azithromycin is the preferred empirical agent for bacterial gastroenteritis 7
• Azithromycin dosing: 10 mg/kg on Day 1, followed by 5 mg/kg on Days 2-5 7
• Common side effects of azithromycin include diarrhea/loose stools (5.8%), abdominal pain (1.9%), vomiting (1.9%), and nausea (1.9%) 7

Supportive Care

• Resume age-appropriate diet immediately during or after rehydration, as early refeeding reduces severity and duration of illness 3, 6
• Continue breastfeeding if applicable 6
• Avoid antimotility agents (loperamide is contraindicated in children <18 years) 3, 6
• Consider ondansetron (0.15 mg/kg) if vomiting prevents adequate oral rehydration 3, 6

Red Flags Requiring Hospitalization

Admit the infant if any of the following are present:

• Severe dehydration (≥10% fluid deficit) with signs of shock 3, 6
• Altered mental status indicating severe dehydration or sepsis 3, 6
• Failure of oral rehydration therapy despite ondansetron 3, 6
• Bloody stools with fever and systemic toxicity suggesting invasive bacterial infection 1, 3, 6
• Persistent tachycardia or hypotension despite initial fluid resuscitation 6
• Infants <3 months warrant lower threshold for admission given higher risk 6

Monitoring During Treatment

• Monitor vital signs every 2-4 hours including capillary refill, skin turgor, mental status, and mucous membrane moisture 6
• Track daily weights to assess rehydration progress 6
• Reassess hydration status after 2-4 hours of ORS administration 6
• If hemolytic uremic syndrome (HUS) is suspected (especially with E. coli O157 or STEC), frequently monitor hemoglobin, platelet counts, electrolytes, BUN, and creatinine 1

Common Pitfalls to Avoid

• Do not delay antibiotic therapy while awaiting culture results when PCT is elevated and bacterial infection is suspected 1
• Do not rely solely on WBC or CRP to rule out bacterial infection, as PCT has higher specificity 1
• Do not withhold food during rehydration, as early refeeding improves outcomes 3, 6
• Do not use fecal leukocyte examination alone to establish the cause, as it performs poorly especially in inpatients 1
• Do not underestimate dehydration in infants, who are more prone to rapid fluid loss due to higher body surface-to-weight ratio 6