Abstract
Background: Staphylococcus aureus colonization is a risk factor for invasive disease. Few studies have used strain genotype data to study S. aureus acquisition and carriage patterns. We investigated S. aureus nasopharyngeal carriage in infants in an intensively sampled South African birth cohort.Methods: Nasopharyngeal swabs were collected at birth and fortnightly from 137 infants through their first year of life. S. aureus was characterized by spa-typing. The incidence of S. aureus acquisition, and median carriage duration for each genotype was determined. S. aureus carriage patterns were defined by combining the carrier index (proportion of samples testing positive for S. aureus) with genotype diversity measures. Persistent or prolonged carriage were defined by a carrier index ≥0.8 or ≥0.5, respectively. Risk factors for time to acquisition of S. aureus were determined.Results: Eighty eight percent (121/137) of infants acquired S. aureus at least once. The incidence of acquisition at the species and genotype level was 1.83 and 2.8 episodes per child-year, respectively. No children had persistent carriage (defined as carrier index of >0.8). At the species level 6% had prolonged carriage, while only 2% had prolonged carriage with the same genotype. Carrier index correlated with the absolute number of spa-CCs carried by each infant (r = 0.5; 95% CI 0.35–0.62). Time to first acquisition of S. aureus was shorter in children from households with ≥5 individuals (HR 1.06, 95% CI 1.07–1.43), with S. aureus carrier mothers (HR; 1.5, 95% CI 1.2–2.47), or with a positive tuberculin skin test during the first year of life (HR; 1.81, 95% CI 0.97–3.3).Conclusion: Using measures of genotype diversity, we showed that S. aureus NP carriage is highly dynamic in infants. Prolonged carriage with a single strain occurred rarely; persistent carriage was not observed. A correlation was observed between carrier index and genotype diversity.
Highlights
Staphylococcus aureus colonizes the mucosal and epithelial surfaces of several body sites such as the nose, throat, gut, axilla, groin, vagina, and perineum
We show that whilst acquisition is common, persistent or prolonged carriage with the same genotype is rare in infants
There were 125 maternal NP swabs obtained at the time of birth, of which 21/125 (17%) yielded S. aureus on culture
Summary
Staphylococcus aureus colonizes the mucosal and epithelial surfaces of several body sites such as the nose, throat, gut, axilla, groin, vagina, and perineum. Longitudinal studies describe three nasal carriage patterns based on the carrier index (the proportion of samples collected from each individual which are positive for S. aureus). Definitions of carriage are influenced by the frequency of sampling, the number of swabs collected and follow up period, which vary between studies (Van Belkum et al, 2009; Muthukrishnan et al, 2013; Verhoeven et al, 2014); seven swabs collected prospectively over 5 weeks were shown to distinguish S. aureus non-carriers from intermittent carriers (Nouwen et al, 2004). Staphylococcus aureus colonization is a risk factor for invasive disease. We investigated S. aureus nasopharyngeal carriage in infants in an intensively sampled South African birth cohort
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