Etiology of Newborn Thrush
Newborn thrush is primarily caused by vertical transmission of Candida albicans from maternal vaginal colonization during delivery, with 70-85% of infants born to colonized mothers acquiring the organism subpartally, though only a subset develop clinical disease. 1
Primary Transmission Route
- Vaginal-to-oral transmission during birth is the dominant mechanism, occurring when the infant passes through the birth canal of a mother with vaginal candidiasis. 1
- At term, 25-30% of pregnant women have C. albicans in vaginal secretions, and approximately 22-24% of all newborns acquire C. albicans during delivery. 1
- The gastrointestinal tract serves as the natural reservoir for Candida species, with vaginal colonization occurring through spread from this primary source. 2
Key Risk Factors
Maternal Factors
- Maternal vaginal candidiasis at delivery is the single most important risk factor, with colonized mothers transmitting the organism to 70-85% of their infants. 1
- Intrapartum antibiotic exposure significantly increases risk, with antibiotic-exposed neonates showing higher rates of thrush (odds ratio 1.87), though this did not reach statistical significance in one study. 3
- Maternal mastitis and antibiotic use were significantly associated with neonatal thrush (p = .001). 4
- Maternal breast candidiasis creates a continuous source of C. albicans, resulting in persistent thrush through the breastfeeding cycle. 5
Infant Factors
- Prematurity and lower gestational age increase susceptibility, with younger infants (mean 38.5 weeks vs. 39.0 weeks) showing higher rates. 3
- Exposure to broad-spectrum antibacterial agents (particularly third-generation cephalosporins and carbapenems) increases risk in neonates. 6
Important Clinical Caveats
Diagnostic Uncertainty
- Clinical diagnosis based solely on white oral patches may be unreliable—a recent study found C. albicans was not discovered in any babies with clinical thrush, and only one infant (3%) without clinical signs had Candida parapsilosis. 4
- The etiology of white patches often remains unclear, and they may not represent true candidiasis. 4
- Diagnosis typically relies on history and physical examination rather than microbiological confirmation. 7, 8
Prevention Strategies
- Treatment of maternal vaginal candidiasis prior to delivery may prevent subsequent neonatal colonization, making prepartal antifungal prophylaxis with intravaginal polyene or azole antimycotics at the end of pregnancy a reasonable strategy. 6, 1
- However, GBS colonization (present in 10-30% of women) requires intrapartum antibiotic prophylaxis, which paradoxically increases candidiasis risk. 2, 3