Source of the conjunctival bacterial flora at birth and implications for ophthalmia neonatorum prophylaxis

To understand better the source of conjunctival bacteria in neonates, we studied 106 infants immediately after birth before any eyedrops were applied. The 50 infants delivered by cesarean section had significantly fewer species (0.50 +/- 0.85 vs 1.84 +/- 1.33) and colony forming units (272 +/- 1,019 vs 1,790 +/- 3,779) cultured per subject than the 56 infants delivered vaginally. In infants delivered by cesarean section within three hours of membrane rupture, 24 of 30 (80%) of the conjunctival cultures were sterile, while the rest bore a few cutaneous bacteria (0.23 +/- 0.50 species and 2 +/- 9 colony forming units per subject). The conjunctivae of infants delivered vaginally bore significantly more bacteria characteristic of vaginal flora: microaerophilic as Lactobacillus or truly anaerobic as Bifidobacterium. Neonates delivered by cesarean section more than three hours after membrane rupture showed a bacteriologic flora mixture quantitatively and qualitatively midway between those two groups. Infants delivered by cesarean section within three hours of membrane rupture may not need prophylactic eyedrops because of the type and scarcity of conjunctival bacteria.