Nasal carriage of methicillin-resistant Staphylococcus aureus during the first 2 years of life in children in northern Taiwan

Background: Most reported studies of methicillin-resistant Staphylococcus aureus (MRSA) carriage have represented 1 time point. To better understand dynamic changes of nasal MRSA carriage, we conducted this longitudinal study in Taiwan. Methods: We recruited 304 newborn babies and obtained samples from nares for detection of S. aureus within 3 days of life, and obtained further samples periodically up to 2 years of age. A total of 12 samplings were attempted to be obtained. Results: Totally, 273 subjects with ≥9 samples were included for analysis. One hundred and ten subjects (40%) harbored MRSA, on one or more occasions; of these 82 (75%) had ≥2 positive specimens and 84 (76%) had colonization ≤4 months of age. Fourteen infants (5.1%) carried MRSA within 3 days of life, the rate peaked at the age of 2 months (21%) and it was lowest (3.1%) at the age of 18 months. All but 4 first MRSA isolates from the colonized subjects carried either staphylococcal cassette chromosome (SCCmec) IV or V_T. Of 32 subjects with ≥4 MRSA isolates, all isolates from the same subject were genetically indistinguishable in 17 (53%) and genetically related in an additional 9 (28%). Five episodes of skin and soft tissue infections (SSTIs) were identified in 4 subjects. Conclusion: In Taiwan, during the first 2 years of life, two-fifths of the children ever harbored MRSA, whereas fewer than 2% of them had SSTIs. Three-fourths of the colonization occurred within the first 4 months and were persistent. More than half of the persistent colonizing isolates were genetically indistinguishable.