Multi-site and nasal swabbing for carriage of Staphylococcus aureus: what does a single nose swab predict?

Background Carriage of Staphylococcus aureus is a risk for infections. Targeted decolonization reduces post-operative infections but depends on accurate screening. Aim We compared detection of S. aureus carriage in healthy individuals between anatomical sites and nurse-versus self-swabbing. Additionally, we aimed to determine whether a single nasal swab predicted carriage over four weeks. Methods Healthy individuals were recruited via General Practices. After consent, nurses performed multi-site swabbing (nose, throat and axilla). Participants performed nasal swabbing twice-weekly for four weeks. Swabs were returned by mail and cultured for S. aureus. All S. aureus isolates underwent spa typing. Persistent carriage in individuals returning more than three self-swabs was defined as culture of S. aureus from all or all but one self-swabs. Findings 102 individuals underwent multi-site swabbing; S. aureus carriage was detected from at least one site from 40 individuals (39%). There was no difference between nose (29/102, 28%) and throat (28/102, 27%) isolation rates: the combination increased total detection rate by 10%. 99 patients returned any self-swab, and 96 returned more than three. Nasal carriage detection was not significantly different on nurse or self-swab (28/99 (74%) versus 26/99 (72%), chi-squared p=0.75). 22/25 participants with first self-swab positive were persistent carriers and 69/71 with first self-swab negative were not, giving high Positive Predictive Value (PPV=88%), and very high Negative Predictive Value (NPV=97%). Conclusions Nasal swabs detected the majority of carriage; throat swabs increased detection by 10%. Self-taken nasal swabs were equivalent to nurse-taken swabs and predicted persistent nasal carriage over four weeks