The turnover of strains in intermittent and persistent nasal carriers of Staphylococcus aureus

Objectives: We aimed to examine the dynamics of Staphylococcus aureus nasal carriage in healthy adults. Method: Selected S. aureus strains isolated from weekly nasal swabs obtained from 122 healthy young adults over a 13 week period were spa typed. Results: The median duration of intermittent carriage was 4 weeks (IQR 2-6) and the median interval between episodes of carriage of different spa types was 3.5 weeks (IQR 2.25-4). 6/19 (32%) Persistent carriers were colonised with more than one spa type during the study, and in two persistent carriers a brief period of mixed colonisation with two spa types was observed. Even when the carriage strain changed, it was very rare for persistent carriers to have a period during which they were culture-negative (only 6/188 (3%) swabs submitted by persistent carriers failed to culture S. aureus). Conclusions: Our results imply that at least every eight weeks a healthy young adult is exposed to S. aureus sufficient to cause a new episode of carriage among intermittent carriers. Persistent carriers are almost always colonised with S. aureus and over the course of a year there will be at least one replacement of the dominant strain. (C) 2016 The British Infection Association. Published by Elsevier Ltd. All rights reserved.