Predicting the Staphylococcus aureus Nasal Carrier State: Derivation and Validation of a “Culture Rule”

• Published in: Clinical infectious diseases Vol. 39; no. 6; pp. 806 - 811
• Main Authors: Nouwen, Jan L., Ott, Alewijn, Kluytmans-Vandenbergh, Marjolein F. Q., Boelens, Hélène A. M., Hofman, Albert, van Belkum, Alex, Verbrugh, Henri A.
• Format: Journal Article
• Language: English
• Published: Chicago, IL The University of Chicago Press 15.09.2004; University of Chicago Press
• Subjects: Adult; Bacterial diseases; Bacteriological Techniques; Biological and medical sciences; Carrier State - diagnosis; Carrier State - epidemiology; Cultural values; Female; Geometric mean; Human bacterial diseases; Humans; Infections; Infectious diseases; Logistic regression; Major Articles; Male; Medical sciences; Middle Aged; Modeling; Nasal carriers; Nasal Cavity - microbiology; Older adults; Predictive Value of Tests; Reproducibility of Results; Risk; Staphylococcal Infections - diagnosis; Staphylococcal Infections - epidemiology; Staphylococcal infections, streptococcal infections, pneumococcal infections; Staphylococcus; Staphylococcus aureus; Staphylococcus aureus - isolation & purification; Human; Prognosis; Healthy subject; Characteristic; Samplings; Nasopharynx; Method; Infection; Negative result; Intermittent; Risk factor; Bacteriosis; Predictive value; Bacteria; Micrococcales; Micrococcaceae; Models; Predictive factor; Staphylococcal infection; Elderly; Colonization; Staphylococcus aureus; Quantitative analysis
• ISSN: 1058-4838; 1537-6591
• DOI: 10.1086/423376

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.