Epidemiology and risk factors for Staphylococcus aureuscolonization in children in the post-PCV7 era

Abstract

BackgroundThe 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.MethodsSwabs 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.ResultsAmong 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. ≥5 yrs, OR 0.39 [95% CI 0.24–0.64]; 1–1.99 yrs vs. ≥5 yrs, OR 0.35 [0.23–0.54]; 2–2.99 yrs vs. ≥5 yrs, OR 0.45 [0.28–0.73]; 3–3.99 yrs vs. ≥5 yrs, OR 0.53 [0.33–0.86]) and recent antibiotic use were significant predictors in multivariate models.ConclusionIn 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.

Staphylococcus aureusandStreptococcus pneumoniaeinteraction and response to pneumococcal vaccination: Myth or reality?

“…2,3 During the following years multiple epidemiological studies in different geographical regions observed similar findings of a negative association between carriage of S. pneumoniae and S. aureus in young children. [4][5][6][7][8] The carriage of both species was associated with age, with the peak S. pneumoniae carriage and lowest S. aureus carriage at 6 months to 3 years [4][5][6][7][8][9][10] and peak S. aureus colonization at age <6 months and 5-7 y 11 The negative association was significant even after adjusting for age, but this interference was not observed in older children and adults. 8,12 Interestingly, most studies 2,3,5,9 found that the inverse correlation between S. pneumoniae and S. aureus was significant only for carriage of vaccine-type S. pneumoniae strains, which were carried more commonly before the introduction of the pneumococcal vaccine.…”

“…7,11,[76][77][78][81][82][83][84] Studies that observed increased S. aureus carriage in children age 11 months no longer saw this increase by age 24 months. 76 …”

“…11 The lack of observed interference is possibly due to the low rates of vaccine-type S. pneumoniae in their samples which were collected following PCV7 vaccination. 11,76 The correlation could also be hidden in the sample due to the large age range of children in their study ranging from 3 months to 7 y Other studies that looked at older children, or looked at a wide range of children without differentiating between older and younger children did not see the individual or population level interference either, 12,77 whereas those that only looked at children under the age of 2 y saw the interference more clearly. 10 It is therefore difficult to interpret the results of this study regarding the effect of PCV7 on S. aureus carriage, particularly since they did not observe an inverse correlation throughout their study periods.…”

“…Since vaccine-type strains were those found to be correlated with S. aureus carriage, this raised much concern that the introduction of the vaccine would indirectly cause a rise in S. aureus carriage and infection. 7,11,14,15 The idea that external interventions in ecosystems could damage the natural equilibrium by eliminating a less virulent 'predator' and result in undesirable emergence of a possibly more virulent 'prey' is not new and was shown decades ago for pests and pesticides. 74 The clinical trial that first suggested interference between S. pneumoniae and S. aureus found a rise in S. aureus otitis media cases following vaccination with PCV7 compared to a non-vaccinated group.…”

Characterisation of virulence genes in methicillin susceptible and resistant Staphylococcus aureus isolates from a paediatric population in a university hospital of Medellín, Colombia

“…This could be explained by the high rates of anterior nares' carriage in the paediatric population, which is associated with subsequent infection (Miller & Diep 2008, Lee et al 2009). …”