Epidemiology and risk factors for Staphylococcus aureus colonization in children in the post-PCV7 era.
BACKGROUND
The incidence of community-associated methicillin-resistant Staphylococcus aureus (MRSA) has risen dramatically in the U.S., particularly among children. Although Streptococcus pneumoniae colonization has been inversely associated with S. aureus colonization in unvaccinated children, this and other risk factors for S. aureus carriage have not been assessed following widespread use of the heptavalent pneumococcal conjugate vaccine (PCV7). Our objectives were to (1) determine the prevalence of S. aureus and MRSA colonization in young children in the context of widespread use of PCV7; and (2) examine risk factors for S. aureus colonization in the post-PCV7 era, including the absence of vaccine-type S. pneumoniae colonization.


METHODS
Swabs of the anterior nares (S. aureus) were obtained from children enrolled in an ongoing study of nasopharyngeal pneumococcal colonization of healthy children in 8 Massachusetts communities. Children 3 months to <7 years of age seen for well child or sick visits in primary care offices from 11/03-4/04 and 10/06-4/07 were enrolled. S. aureus was identified and antibiotic susceptibility testing was performed. Epidemiologic risk factors for S. aureus colonization were collected from parent surveys and chart reviews, along with data on pneumococcal colonization. Multivariate mixed model analyses were performed to identify factors associated with S. aureus colonization.


RESULTS
Among 1,968 children, the mean age (SD) was 2.7 (1.8) years, 32% received an antibiotic in the past 2 months, 2% were colonized with PCV7 strains and 24% were colonized with non-PCV7 strains. The prevalence of S. aureus colonization remained stable between 2003-04 and 2006-07 (14.6% vs. 14.1%), while MRSA colonization remained low (0.2% vs. 0.9%, p = 0.09). Although absence of pneumococcal colonization was not significantly associated with S. aureus colonization, age (6-11 mo vs. > or =5 yrs, OR 0.39 [95% CI 0.24-0.64]; 1-1.99 yrs vs. > or =5 yrs, OR 0.35 [0.23-0.54]; 2-2.99 yrs vs. > or =5 yrs, OR 0.45 [0.28-0.73]; 3-3.99 yrs vs. > or =5 yrs, OR 0.53 [0.33-0.86]) and recent antibiotic use were significant predictors in multivariate models.


CONCLUSIONS
In Massachusetts, S. aureus and MRSA colonization remained stable from 2003-04 to 2006-07 among children <7 years despite widespread use of pneumococcal conjugate vaccine. S. aureus nasal colonization varies by age and is inversely correlated with recent antibiotic use.
Lee
Grace M
GM
Department of Population Medicine, Harvard Pilgrim Health Care Institute and Harvard Medical School, Boston, MA, USA. grace_lee@hphc.org
Huang
Susan S
SS
Rifas-Shiman
Sheryl L
SL
Hinrichsen
Virginia L
VL
Pelton
Stephen I
SI
Kleinman
Ken
K
Hanage
William P
WP
Lipsitch
Marc
M
McAdam
Alexander J
AJ
Finkelstein
Jonathan A
JA
D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D005260:Female; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D007223:Infant; D016015:Logistic Models; D008297:Male; D008404:Massachusetts / Q000453:epidemiology; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D015999:Multivariate Analysis; D009296:Nasal Cavity / Q000382:microbiology; D022242:Pneumococcal Vaccines / Q000627:therapeutic use*; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology
D000900:Anti-Bacterial Agents; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022242:Pneumococcal Vaccines