Predicting the Staphylococcus aureus nasal carrier state: derivation and validation of a "culture rule".

BACKGROUND: To study determinants and risks of Staphylococcus aureus nasal carriage, adequate differentiation between the different S. aureus carrier states is obligatory. We set out to develop a "culture rule" capable of differentiating between persistent and intermittent or noncarriers that uses a minimum of nasal swab cultures. METHODS: In 51 healthy volunteers (derivation cohort), 12 quantitative nasal cultures were performed to establish S. aureus nasal carriage states. Persons with 11 or 12 cultures positive for S. aureus were classified as persistent carriers, and those with negative results of all cultures were classified as noncarriers. All other persons were classified as intermittent carriers. By means of logistic regression and receiver operating characteristic (ROC) curves, a culture rule was derived. This culture rule was subsequently validated in 106 participants of an ongoing study in 3882 elderly persons, again with the use of 12 quantitative nasal cultures. RESULTS: In both cohorts, the positive predictive value of 2 consecutive positive culture results for persistent carriage was 79%. The model best differentiating between persistent and intermittent or noncarriers used the number of positive culture results combined with the amount of S. aureus in these cultures. By using the outcome of 2 cultures, the areas under the ROC curves were 0.981 (95% confidence interval [CI], 0.949-1.0) for the derivation cohort and 0.936 (95% CI, 0.881-0.990) for the validation cohort. CONCLUSIONS: Combining qualitative and quantitative results of 2 nasal swab cultures accurately predicted the persistent S. aureus carriage state with a reliability of 93.6%. Thus, this culture rule can be used in studies of determinants and risks of S. aureus nasal carriage.

Measuring the quality of infection control in Dutch nursing homes using a standardized method; the Infection prevention RIsk Scan (IRIS).

BACKGROUND: We developed a standardised method to assess the quality of infection control in Dutch Nursing Home (NH), based on a cross-sectional survey that visualises the results. The method was called the Infection control RIsk Infection Scan (IRIS). We tested the applicability of this new tool in a multicentre surveillance executed June and July 2012. METHODS: The IRIS includes two patient outcome-variables, i.e. the prevalence of healthcare associated infections (HAI) and rectal carriage of Extended-Spectrum Beta-Lactamase (ESBL) producing Enterobacteriaceae (ESBL-E); two patient-related risk factors, i.e. use of medical devices, and antimicrobial therapy; and three ward-related risk factors, i.e. environmental contamination, availability of local guidelines, and shortcomings in infection prevention preconditions. Results were categorised as low-, intermediate- and high risk, presented in an easy-to-read graphic risk spider-plot. This plot was given as feedback to management and healthcare workers of the NH. RESULTS: Large differences were found among most the variables in the different NH. Common shortcomings were the availability of infection control guidelines and the level of environmental cleaning. Most striking differences were observed in the prevalence of ESBL carriage, ranged from zero to 20.6% (p < 0.001). CONCLUSIONS: The IRIS provided a rapid and easy to understand assessment of the infection control situation of the participating NH. The results can be used to improve the quality of infection control based on the specific needs of a NH but needs further validation in future studies. Repeated measurement can determine the effectiveness of the interventions. This makes the IRIS a useful tool for quality systems.