Pernasal and throat swabs taken on 106 newborn babies showed that 99% harboured coagulase-positive Staph. aureus by the time they left the hospital nursery. When the strains isolated from thirty-four of them were phage typed and tested for penicillin sensitivity, it was found that thirty-three (97%) carried at least one penicillin-resistant strain. Phage typing of their subsequent cultures, taken as they became older, demonstrated that they retained these strains for very long periods. Of the twenty-one still under observation at 6 months of age, eleven (53%) were carrying one or more of their original hospital strains, and an additional three (14%) still were consistently yielding an untypable strain believed to be identical to that acquired in hospital. Similarly, of those remaining under observation for the last 6 months of their first year, at least 50% continued to carry their hospital strains.

These babies frequently retained the hospital strains in their throats longer than in their noses. Although their nasal cultures often became negative after the first few months of life, the original hospital strains continued to be recovered from the throats. This would indicate that the throat culture is more accurate than the nasal culture in determining staphylococcal carriers among this age group. Antibiotic-resistant staphylococci in the infant throat may have considerable epidemiological significance, since babies tend to widely distribute their saliva.

The observations suggest that the staphylococci acquired at birth become a normal component of the upper respiratory flora, and may thus prevent new strains of staphylococci from becoming established later. This may explain why newborn babies retain the antibiotic-resistant staphylococci of the hospital much longer than do adult patients. Antibiotic-resistant strains among the general non-hospital population will be increased steadily by babies born in hospitals.