title: Factors Affecting Staphylococcus aureus Colonization of the Nasopharynx in the First 6 Months of Life.
abstract: BACKGROUND
  Staphylococcal aureus (SA) colonization in early infancy is common, but the pattern and factors affecting its acquisition and persistence in the first few months of life are not well studied. The aim is to study the rate of SA nasopharyngeal (NP) colonization at monthly intervals in the first 6 months of life and its association with environmental and host factors and other pathogenic NP bacteria.
  
  
  METHODS
  Data from a prospective study were analyzed on bacterial cultures of 1765 NP swabs from 367 infants who were followed from birth to 6 months of age. Demographic, breastfeeding, cigarette smoke exposure and day care attendance data were collected at each monthly visit.
  
  
  RESULTS
  The rate of infants colonized with SA was highest at age 1 month (25%) and declined to lowest rate by age 6 months (12%). The proportion of SA strains that was methicillin-resistant SA was also highest at age 1 month and declined rapidly by age 4 months (18% vs. 6%, P = 0.05). Colonization with Streptococcus pneumoniae (SP), nontypeable Haemophilus influenzae (NTHI) and Moraxella catarrhalis (MC) increased at different rates up to age 6 months. Univariate analysis showed that SA colonization rate was significantly lower with increasing age, black race, day care attendance, and colonization with NTHI, MC and SP (P < 0.05). Multivariate analysis showed that this effect was independently associated only with increasing age and MC colonization (P < 0.05). Furthermore, the time to first acquisition of SA from one month of age onwards was significantly associated with day care attendance, and NTHI and MC colonization. None of the infants colonized with SA developed SA infections through age 6 months.
  
  
  CONCLUSIONS
  SA colonization of NP begins very early in life and declines quickly. Methicillin-resistant SA has lower ability to maintain prolonged colonization status than methicillin-susceptible strains in the first 6 months of life. As the NP is colonized with other respiratory bacterial pathogens, the colonization with SA declines; however, this effect is stronger with Gram-negative bacteria, such as NTHI and MC.
authors.affiliation: From the *Department of Pediatrics, †Department of Preventive Medicine and Community Health, ‡Department of Pathology, University of Texas Medical Branch, Galveston, Texas.
authors.forename: Janak A
authors.initials: JA
authors.lastname: Patel
authors.forename: Pedro
authors.initials: P
authors.lastname: Alvarez-Fernandez
authors.forename: Kristofer
authors.initials: K
authors.lastname: Jennings
authors.forename: Michael
authors.initials: M
authors.lastname: Loeffelholz
authors.forename: David
authors.initials: D
authors.lastname: McCormick
authors.forename: Tasnee
authors.initials: T
authors.lastname: Chonmaitree
mesh_terms: D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000382:microbiology*; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus; D013781:Texas / Q000453:epidemiology