Molecular studies of an impetigo bullosa epidemic in full-term infants

Carriers of Staphylococcus aureus strains can be the source of epidemic infection for patients.

A molecular epidemiological analysis of an impetigo bullosa outbreak in a neonatal ward was performed in order to determine a potential source of the infection and possible routes of subsequent spreading of the epidemic strain.

The genetic relatedness of S. aureus strains isolated from 6 neonates with epidermal lesions and from 21 staff members was verified by the pulsed field gel electrophoresis (PFGE) method. Additionally, detection of eta and etb genes of S. aureus strains using PCR was performed.

None of the infected newborns' mothers was a carrier. Seven strains, 6 isolated from the newborns and 1 taken from a midwife, showed the same restriction pattern, i.e. type A. In the other 20 health care workers colonized with S. aureus, 3 genetic types could be distinguished, i.e. B (2), C (7) and D (2), as well as 9 strains with unique PFGE patterns. The eta gene detected in 7 strains belonged to the genetic type A; there was no etb gene in any of the 27 S. aureus isolates.

The presence of the same genetic type A of S. aureus in the infected newborns is a factor which indicates that the impetigo bullosa was a hospital infection. A probable source of the infection was a midwife who was colonized with the same S. aureus type. She was present at the birth of the first infected newborn. Today, molecular methods are essential for prompt recognition of an epidemic and implementation of appropriate infection control strategies.