Sampling methods to detect carriage of Neisseria meningitidis; literature review

Studies of meningococcal carriage are important in understanding the epidemiology of meningococcal disease and the impact of vaccination programmes. However, microbiological sampling methods to determine pharyngeal carriage are not consistent between studies and the optimal method is uncertain.

A comprehensive literature search was undertaken using Medline, Embase and the Cochrane Library (Feb 2008) to identify studies comparing isolation rates using different sampling methods.

Four studies compared isolation of meningococci from different pharyngeal sites. Nasopharyngeal swabs taken through the nose were less likely to yield meningococcal cultures than pharyngeal swabs taken through the mouth. One study investigated different sampling sites using swabs taken through the mouth and found higher yields from the posterior pharyngeal wall compared to the tonsils (32.2% cf 19.4%, p=0.001). Four studies compared the yield obtained using transport medium to direct plating. Loss of yield in transport medium ranged from 5.7% to 16.4% after storage for >5h.

The evidence to date suggests that meningococcal carriage should be assessed by swabbing the posterior pharyngeal wall through the mouth, and that swabs should be plated directly on site or placed in transport medium for <5h.

The current literature suggests meningococcal carriage is best assessed by swabbing the posterior pharyngeal wall through the mouth with direct plating or keeping transport time to below 5h. Whether a swab taken from both the posterior pharynx and the tonsils improves yield further needs evaluation.