Crystal violet reactions of Staphylococcus aureus strains colonizing infants in the first six weeks.

Nasal colonization with Staphylococcus aureus occurred in 18% of babies leaving a maternity unit and had risen to 40% by 6 weeks after birth. S. aureus was first acquired by 34.5% of babies after discharge. Female infants were more likely to be colonized than males. Colonization was not significantly different between babies receiving standard postnatal care and those nursed on the Special Care Baby Unit. Crystal violet (CV) tests showed that purple-reacting isolates accounted for approximately 60% of strains, whether first detected at hospital discharge or subsequently acquired. Purple-reacting strains, once acquired, were significantly better able to persist than non purple-reacting strains and formed a cumulatively higher proportion of the strains isolated at 6 weeks after birth than at hospital discharge. CV purple-reactions were significantly associated with lysis by phages of groups III and I and non-purple-reactions were significantly associated with lysis by phages of group II and/or 94/96. Maternity units remain a significant route whereby strains of S. aureus with some characteristics associated with a hospital origin gain access to the community.