What Causes Oral Thrush in Infants
Oral thrush in infants is caused by overgrowth of Candida species, most commonly Candida albicans, a yeast fungus that colonizes the oral mucosa. 1, 2
Primary Causative Organism
- Candida albicans is the predominant pathogen responsible for oral thrush in infants, affecting the mucous membranes of the tongue, palate, cheeks, and lips 3, 2
- Other Candida species (C. parapsilosis, C. tropicalis) are seen less commonly in neonates 3
Mechanism of Infection
The infection develops through colonization and subsequent overgrowth of Candida in the oral cavity, which can occur through several pathways:
Maternal Transmission
- Neonatal colonization occurs from maternal vaginal candidiasis during delivery, making treatment of maternal vaginal candidiasis prior to delivery an important preventive measure 3, 4
- Contamination of amniotic fluid can lead to congenital candidiasis, particularly with prolonged rupture of membranes 3
Environmental Factors
- Horizontal transmission in healthcare settings (particularly NICUs) through inadequate infection control measures 3
- Reinfection from contaminated pacifiers, bottles, and toys that harbor Candida 5, 4
- Breastfeeding-associated transmission when maternal nipples are colonized 4
Risk Factors for Development
In Premature/High-Risk Neonates
The following factors significantly increase risk of Candida infections in the NICU setting:
- Prematurity and low birth weight (infants <1000g have >10% incidence of invasive candidiasis) 3
- Exposure to broad-spectrum antibacterial agents, particularly third-generation cephalosporins and carbapenems 3
- Central vascular catheterization 3
- Parenteral nutrition and antacid use 3
- Endotracheal intubation 3
- Abdominal surgery or necrotizing enterocolitis 3
In Otherwise Healthy Infants
- Immature immune system in young infants makes them susceptible to Candida overgrowth 1
- Maternal mastitis and maternal antibiotic use are significantly associated with thrush development 6
Important Clinical Caveat
Recent evidence suggests that not all white patches in infant mouths are caused by Candida albicans. A 2019 study found that C. albicans was not discovered in babies with clinical thrush, and only one infant without clinical signs had Candida parapsilosis 6. This highlights that while Candida species remain the presumed cause, the etiology of white patches may sometimes remain unclear and other factors may contribute to the clinical presentation 6.