# When Coagulase-Negative Staphylococci Mislead: Transient Metabolic Acidosis in a Healthy Toddler

## TL;DR

A healthy toddler developed temporary metabolic acidosis linked to a rare Staphylococcus hominis blood culture, highlighting the need for careful diagnosis to avoid unnecessary antibiotics.

## Contribution

This case highlights the diagnostic challenge of coagulase-negative staphylococci in pediatric patients with transient metabolic acidosis.

## Key findings

- A previously healthy toddler presented with transient metabolic acidosis and S. hominis bacteremia.
- Clinical improvement occurred with supportive care, suggesting non-infectious causes for acidosis.
- True S. hominis infections are rare in immunocompetent children and often linked to severe conditions.

## Abstract

Staphylococcus hominis (S. hominis), a coagulase-negative staphylococcus (CoNS), is commonly encountered in blood cultures and presents diagnostic challenges in both pediatric and adult infections. Its clinical significance remains uncertain, especially in previously healthy children without evident immunodeficiency or indwelling devices. Metabolic acidosis associated with S. hominis bacteremia is rarely reported, further complicating clinical interpretation. We report a previously healthy two-year-old boy presenting with high-grade fever, cough, mild respiratory distress, and metabolic acidosis (pH 7.28, bicarbonate 12 mmol/L). Initial blood culture yielded S. hominis, while subsequent cultures remained negative. The patient had no immunodeficiency or indwelling devices. Clinical improvement occurred rapidly with supportive care, inhaled bronchodilators, intravenous fluids, short-course corticosteroids, and intravenous antibiotics based on antibiogram. Based on the above, the diagnosis was transient metabolic acidosis associated with viral/bacterial respiratory tract infection. Symptoms resolved within 48 hours, with complete normalization of laboratory parameters. The S. hominis isolate was evaluated based on clinical and microbiological reassessment, allowing antibiotic de-escalation and discharge on day four of admission. Differentiating true CoNS infection from contamination is critical in pediatric settings to prevent unnecessary antibiotic exposure. True S. hominis infections are exceedingly rare in immunocompetent children and typically associated with severe clinical manifestations and underlying risk factors. The transient metabolic acidosis observed likely resulted from mild dehydration and catabolic stress rather than direct bacterial effects. This case underscores the necessity for cautious interpretation of isolated CoNS-positive cultures, highlighting the importance of clinical correlation, repeated cultures, and careful risk assessment. The diagnostic dilemma presented by a single positive S. hominis blood culture in pediatric patients with transient metabolic acidosis emphasizes the need for judicious interpretation to avoid overtreatment. Further studies are warranted to better characterize the clinical significance of CoNS isolates in immunocompetent pediatric populations.