Persistence, replacement, and rapid clonal expansion of meningococcal carriage isolates in a 2008 university student cohort.

A study of meningococcal carriage dynamics was performed with a cohort of 190 first-year students recruited from six residential halls at Nottingham University, United Kingdom. Pharyngeal swabs were obtained on four occasions between November 2008 and May 2009. Direct plating and culture on selective media were succeeded by identification and characterization of meningococci using PCR-based methodologies. Three serogroup Y clones and one serogroup 29E clone were highly prevalent in particular residential halls in November 2008, which is indicative of rapid clonal expansion since the start of the academic year. Persistent carriage of the same meningococcal strain for at least 5 to 6 months was observed in 45% of carriers, with infrequent evidence of antigenic variation in PorA. Sequential carriage of heterologous meningococcal strains occurred in 36% of carriers and involved strains with different capsules and antigenic variants of PorA and FetA in 83% of the cases. These clonal replacement strains also exhibited frequent differences in the presence and antigenic structures of two other surface proteins, NadA and HmbR. This study highlights the low level of antigenic variation associated with persistent carriage but, conversely, the importance of alterations in the repertoire of antigenic variants for sequential carriage of meningococcal strains. Rapid clonal expansion of potentially pathogenic strains in residential halls has implications for the implementation of public health interventions in university populations.