Evaluation of the timing of MRSA PCR nasal screening: How long can a negative assay be used to rule out MRSA-positive respiratory cultures?

Abstract

Purpose Previous studies indicate that the polymerase chain reaction (PCR) nasal assay for methicillin-resistant Staphylococcus aureus (MRSA) has a consistently high (>95%) negative predictive value (NPV) in ruling out MRSA pneumonia; however, optimal timing of PCR assay specimen and respiratory culture collection is unclear. Methods A study including 736 patients from a community hospital system was conducted. Patients were included if they had undergone MRSA nasal screening with a PCR assay and had documented positive respiratory culture results. Results In the full cohort, the MRSA PCR nasal screen assay was demonstrated to have an NPV of 94.9% (95% confidence interval [CI], 92.8%-96.5%) in ruling out MRSA-positive respiratory cultures. When evaluating the NPV by level of care (ie, where the MRSA PCR nasal assay sample was collected), no significant difference between values for samples collected in an intensive care unit vs medical/surgical units was identified (NPV [95%CI], 94.9% [92.7%-96.6%] vs 95.3% [88.4%-98.7%]).Additionally, NPV remained high with use of both invasive (NPV [95%CI], 96.8% [92.7%-99.0%]) and noninvasive (NPV [95%CI], 94.5% [91.7%-96.2%]) respiratory sampling methods. Finally, when evaluating the effect of time between MRSA PCR nasal screening and respiratory sample collection, we found high NPVs for all evaluated timeframes: within 24 hours, 93.8% (90.1%-96.4%); within 25 to 48 hours, 98.6% (92.7%-100.0%); within 49 hours to 7 days, 95.7% (91.4%-98.3%); within 8 to 14 days, 92.9% (85.1%-97.3%); and after more than 14 days, 95.5% (84.5%-99.4%). Conclusion We report high NPVs for up to 2 weeks between specimen collections, which allows clinicians to use a negative MRSA PCR nasal screen assay to rule out MRSA pneumonia, potentially leading to decreased exposure to MRSA-active antibiotics.

Predictors of discordant MRSA nares and respiratory cultures in patients with pneumonia

“…A recent study reported an NPV of 95.5% when the time between MRSA nares and respiratory sample collection was 14 days. 6 We found that history of MRSA infection and time of ≥7 days between swab and respiratory culture were associated with discordance. However, the low event rate limits the ability to control for other confounders and interpretation of findings should be approached carefully based on the nature of the retrospective design.…”

“… 3–6 However, concerns for swab and respiratory culture discordance remain, and there are a few known risk factors associated with discordant results. 4 , 6 We conducted a single-centre, retrospective, case–control study to evaluate predictors of having a discordant result (negative MRSA nares swab with a positive MRSA respiratory culture) in patients diagnosed with pneumonia. Chi-squared and Fisher’s exact test were used to compare categorical variables and Mann–Whitney U -test was used for continuous variables.…”

“…While these duration cut-off points have been identified in the literature, the NPV remains high even beyond 7 and 14 days. 6 , 8 Mallidi et al 8 calculated an NPV >98% in critically ill patients using a duration between swab and respiratory sample collection of up to 60 days. Ultimately, extrapolation to other institutions is dependent on local prevalence and testing practices.…”

Performance of Methicillin-Resistant Staphylococcus aureus Polymerase Chain Reaction Nasal Screening for Ruling Out MRSA Pneumonia in Hospitalized, Immunocompromised Patients

“…Patients were excluded if confirmatory cultures were not obtained within 2 weeks from the MRSA NaPCR test. 16 Qualifying culture sites included respiratory (bronchoalveolar lavage, sputum, and tracheal aspirate), blood (venous puncture or lines), urine, skin and skin structure (including wound), and intra-abdominal. Augusta University (AU) Medical Center is a 483-bed urban, tertiary referral, academic medical center.…”

Evaluation of computerized clinical decision support system to reduce unnecessary nasal methicillin-resistant Staphylococcus aureus (MRSA) polymerase chain reaction (PCR) testing

“…The Division of Healthcare Quality Promotion within the Centers for Disease Control and Prevention (CDC) has underscored the importance of advancing diagnostic stewardship to enhance treatment, outcomes, and patient safety. 1,2 A recent study conducted by Turner et al 3 assessed the extent to which the nasal methicillin-resistant Staphylococcus aureus (MRSA) polymerase chain reaction (PCR) maintained its negative predictive value (NPV) in ruling out MRSA-positive respiratory cultures relative to the duration of hospitalization. The study highlighted a high NPV of 95.7% from 49 hours to 7 days and 92.9% from 8 to 14 days.…”