Implementation of a diagnostic stewardship intervention to improve blood-culture utilization in 2 surgical ICUs: Time for a blood-culture change

OBJECTIVE

We compared the number of blood-culture events before and after the introduction of a blood-culture algorithm and provider feedback. Secondary objectives were the comparison of blood-culture positivity and negative safety signals before and after the intervention.

DESIGN

Prospective cohort design.

SETTING

Two surgical intensive care units (ICUs): general and trauma surgery and cardiothoracic surgery.

PATIENTS

Patients aged ≥18 years and admitted to the ICU at the time of the blood-culture event.

METHODS

We used an interrupted time series to compare rates of blood-culture events (ie, blood-culture events per 1,000 patient days) before and after the algorithm implementation with weekly provider feedback.

RESULTS

The blood-culture event rate decreased from 100 to 55 blood-culture events per 1,000 patient days in the general surgery and trauma ICU (72% reduction; incidence rate ratio [IRR], 0.38; 95% confidence interval [CI], 0.32-0.46; P < .01) and from 102 to 77 blood-culture events per 1,000 patient days in the cardiothoracic surgery ICU (55% reduction; IRR, 0.45; 95% CI, 0.39-0.52; P < .01). We did not observe any differences in average monthly antibiotic days of therapy, mortality, or readmissions between the pre- and postintervention periods.

CONCLUSIONS

We implemented a blood-culture algorithm with data feedback in 2 surgical ICUs, and we observed significant decreases in the rates of blood-culture events without an increase in negative safety signals, including ICU length of stay, mortality, antibiotic use, or readmissions.

Assessing the Impact of 2-Step Clostridioides difficile Testing at the Healthcare Facility Level

BACKGROUND

Two-step testing for Clostridioides difficile infection (CDI) aims to improve diagnostic specificity but may also influence reported epidemiology and patterns of treatment. Some providers fear that 2-step testing may result in adverse outcomes if C. difficile is underdiagnosed.

METHODS

Our primary objective was to assess the impact of 2-step testing on reported incidence of hospital-onset CDI (HO-CDI). As secondary objectives, we assessed the impact of 2-step testing on C. difficile-specific antibiotic use and colectomy rates as proxies for harm from underdiagnosis or delayed treatment. This longitudinal cohort study included 2 657 324 patient-days across 8 regional hospitals from July 2017 through March 2022. Impact of 2-step testing was assessed by time series analysis with generalized estimating equation regression models.

RESULTS

Two-step testing was associated with a level decrease in HO-CDI incidence (incidence rate ratio, 0.53 [95% confidence interval {CI}, .48-.60]; P < .001), a similar level decrease in utilization rates for oral vancomycin and fidaxomicin (utilization rate ratio, 0.63 [95% CI, .58-.70]; P < .001), and no significant level (rate ratio, 1.16 [95% CI, .93-1.43]; P = .18) or trend (rate ratio, 0.85 [95% CI, .52-1.39]; P = .51) change in emergent colectomy rates.

CONCLUSIONS

Two-step testing is associated with decreased reported incidence of HO-CDI, likely by improving diagnostic specificity. The parallel decrease in C. difficile-specific antibiotic use offers indirect reassurance against underdiagnosis of C. difficile infections still requiring treatment by clinician assessment. Similarly, the absence of any significant change in colectomy rates offers indirect reassurance against any rise in fulminant C. difficile requiring surgical management.

Using clinical decision support to improve urine testing and antibiotic utilization

OBJECTIVE

Urine cultures collected from catheterized patients have a high likelihood of false-positive results due to colonization. We examined the impact of a clinical decision support (CDS) tool that includes catheter information on test utilization and patient-level outcomes.

METHODS

This before-and-after intervention study was conducted at 3 hospitals in North Carolina. In March 2021, a CDS tool was incorporated into urine-culture order entry in the electronic health record, providing education about indications for culture and suggesting catheter removal or exchange prior to specimen collection for catheters present >7 days. We used an interrupted time-series analysis with Poisson regression to evaluate the impact of CDS implementation on utilization of urinalyses and urine cultures, antibiotic use, and other outcomes during the pre- and postintervention periods.

RESULTS

The CDS tool was prompted in 38,361 instances of urine cultures ordered in all patients, including 2,133 catheterized patients during the postintervention study period. There was significant decrease in urine culture orders (1.4% decrease per month; P < .001) and antibiotic use for UTI indications (2.3% decrease per month; P = .006), but there was no significant decline in CAUTI rates in the postintervention period. Clinicians opted for urinary catheter removal in 183 (8.5%) instances. Evaluation of the safety reporting system revealed no apparent increase in safety events related to catheter removal or reinsertion.

CONCLUSION

CDS tools can aid in optimizing urine culture collection practices and can serve as a reminder for removal or exchange of long-term indwelling urinary catheters at the time of urine-culture collection.

Disinfection efficacy of Oxivir TB wipe residue on severe acute respiratory coronavirus virus 2 (SARS-CoV-2)

We assessed Oxivir Tb wipe disinfectant residue in a controlled laboratory setting to evaluate low environmental contamination of SARS-CoV-2. Frequency of viral RNA detection was not statistically different between intervention and control arms on day 3 (P=0.14). Environmental contamination viability is low; residual disinfectant did not significantly contribute to low contamination.

Optimizing reflex urine cultures: Using a population-specific approach to diagnostic stewardship

BACKGROUND

Clinicians and laboratories routinely use urinalysis (UA) parameters to determine whether antimicrobial treatment and/or urine cultures are needed. Yet the performance of individual UA parameters and common thresholds for action are not well defined and may vary across different patient populations.

METHODS

In this retrospective cohort study, we included all encounters with UAs ordered 24 hours prior to a urine culture between 2015 and 2020 at 3 North Carolina hospitals. We evaluated the performance of relevant UA parameters as potential outcome predictors, including sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV). We also combined 18 different UA criteria and used receiver operating curves to identify the 5 best-performing models for predicting significant bacteriuria (≥100,000 colony-forming units of bacteria/mL).

RESULTS

In 221,933 encounters during the 6-year study period, no single UA parameter had both high sensitivity and high specificity in predicting bacteriuria. Absence of leukocyte esterase and pyuria had a high NPV for significant bacteriuria. Combined UA parameters did not perform better than pyuria alone with regard to NPV. The high NPV ≥0.90 of pyuria was maintained among most patient subgroups except females aged ≥65 years and patients with indwelling catheters.

CONCLUSION

When used as a part of a diagnostic workup, UA parameters should be leveraged for their NPV instead of sensitivity. Because many laboratories and hospitals use reflex urine culture algorithms, their workflow should include clinical decision support and or education to target symptomatic patients and focus on populations where absence of pyuria has high NPV.

2240. Implementation of a Clinical Decision Support Panel for Urine Culture Ordering

Background

Standard urine culture collection techniques have a high risk of false positive results in catheterized patients. IDSA guidelines recommend replacing long-term catheters before specimen collection for cultures. Our goal was to evaluate the impact of clinical decision support (CDS) during the urine culture computerized provider order entry (CPOE) on test use and patient-level outcomes.

Methods

In March 2021, CDS was added to the urine culture CPOE in the electronic health record (EHR). The order panel includes education regarding appropriate clinical indications for urine culturing, and protocolizes urine collection to determine (A) if a urinalysis was ordered, (B) if special patient population (i.e., PICU), (C) the presence and duration of an indwelling urinary catheter, and (D) whether the catheter had difficulty with placement. Depending on the criteria identified in A, B, C, and D, the panel recommends catheter removal prior to urine culture (Figure 1). We retrospectively evaluated the impact of panel implementation in our pre- (7/2020- 3/2021) and post-intervention periods (4/2021- 3/2022) using an interrupted time series analysis with Poisson regression. Outcomes included urine cultures/1000 patient days (pd), number of catheter removal orders, catheter-associated urinary tract infection (CAUTI)/1000 catheter days, and days of antibiotic therapy with urinary tract infection (UTI) indication/1000pd

Order Panel Framework

Results

Clinicians selected catheter removal in 183 of 2133 (8.5%) instances of ordering a urine culture when a catheter was detected by the panel (Figure 2). Analysis revealed a significant decrease in urine culture orders (1.1% decrease/month, p< 0.05), a decreasing trend of antibiotic use with UTI indications (Figure 3, 2.8% decrease/month, p< 0.05), but no significant change in CAUTI rates (Figure 4). Evaluation of the safety reporting system revealed no identifiable increase in safety events related to catheter removal or reinsertion.

Catheter Associated Urinary Tract Infections

Black boxes indicate Poisson regression model estimates

Black boxes indicate Poisson regression model estimates

Conclusion

CDS can aid in improving urine culture practice habits, including removal of long-standing catheters before urine culture. The decreasing trend in total urine culture orders (Figure 5) may reflect a ”culture change” over time to avoid urine cultures in inappropriate instances.

Total Urine Cultures Ordered

Black boxes indicate Poisson regression model estimates. Red circles indicate predicted outcome without ‘intervention’.

Disclosures

Sonali D. Advani, MBBS, MPH, FIDSA, Locus Biosciences: Advisor/Consultant|Locus Biosciences: Honoraria|Sysmex America: Advisor/Consultant.

190. Performance of urinalysis parameters in predicting significant bacteriuria: Making the case for a population-specific approach to diagnostic stewardship

Background

Clinicians and laboratories routinely use urinalysis (UA) results to help determine if urine cultures and/or antimicrobials are indicated. Yet, the performance of individual UA parameters and common clinical thresholds for action are not well defined and may vary across different patient populations. Our objective was to compare the performance of different UA parameters in predicting significant bacteriuria irrespective of symptoms, and to assess performance of pyuria based on age, sex, and presence of indwelling catheter.

Methods

This retrospective review of UA and urine culture data from the Duke University Health System included all UAs ordered within 24 hours of a urine culture between 2015 and 2020 (no reflex urine cultures included). We defined significant bacteriuria as a urine culture with ≥1 uropathogen growing at ≥100,000 colony forming units/mL. Then, we used this definition to evaluate the performance of relevant UA parameters and result thresholds including sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV). We also combined 18 different UA criteria (as shown in Figure) and used receiver operating characteristic (ROC) curves to identify the top 5 performing models for predicting significant bacteriuria (sensitivity and specificity).

18 Different Combinations of UA Parameters for Predicting Significant Bacteriuria on Urine Cultures

Results

Of 240,195 encounters during the 6-year study period, 38% were outpatient and 62% were inpatient. Twenty-nine percent had a urine culture with significant bacteriuria; 30.7% had a negative urine culture. No single UA parameter had both - high sensitivity and high specificity in predicting bacteriuria. Trace leukocyte esterase and low-level pyuria had a high NPV for significant bacteriuria (Table 1A). Combined UA parameters did not perform better than pyuria alone (Table 1B). The high NPV >=0.90 of pyuria was maintained among most patient age and sex subgroups with the exception of females ≥65 and patients with indwelling catheters (Table 2). Table 1A:

311. Modeling Diagnostic Testing Strategies for SARS-CoV-2 to Minimize Societal Costs and Return People to Work

Background

The shift to more transmissible but less virulent strains of SARS-CoV-2 has altered the risk calculation for infection. Particularly among young adults, the economic burden of lost work due to isolation exceeds the economic burden of morbidity due to infection. Testing strategies must adapt to these changing circumstances.

Methods

We modeled six testing strategies to estimate total societal costs for symptomatic people 18-49 years old: isolation of all individuals with no testing, rapid antigen test (RAg), RAg followed by a second RAg 48h later if first negative, RAg followed by a polymerase chain reaction (PCR) if negative, RAg followed by a PCR if positive, and PCR alone. We calculated costs for hypothetical cohorts of 100 symptomatic healthcare workers tested with each strategy; we included testing costs, lost wages, and hospitalization costs for the index, secondary, and tertiary cases. Key assumptions were 5% prevalence of infection, sensitivity of first/second RAg 40/80% with 97% specificity, PCR sensitivity/specificity 95/99%, all individuals isolate at symptom onset, are tested the same day, and isolate for 5 days if positive. RAg results were available the same day, PCR results were available the next day (Figure 1). One-way sensitivity analyses were performed for RAg sensitivity (20-80%) and positivity rate (1-80%).

Results

The least expensive strategy was RAg alone (Figure 2). This was primarily driven by its low sensitivity, which reduced lost wages at the expense of missing cases. At a threshold for RAg sensitivity lower than 29%, PCR testing alone became the cheapest strategy. When the positivity rate was &gt; 6% confirming a negative RAg with a PCR became the cheapest strategy, closely followed by PCR alone. At a positivity rate of &gt; 29%, isolation without testing was cheapest followed by confirming a negative RAg with a PCR and by the serial RAg test strategies (Figure 3).

Conclusion

In relatively young, healthy populations, a single rapid test was the least expensive strategy when the positivity rate was &lt; 6%, testing that included PCR became cheapest at intermediate positivity, and empiric isolation was cheapest at positivity &gt; 29%. Calibrating SARS-CoV-2 test strategies based on epidemiology may save societal costs.

Disclosures

Nicholas A. Turner, MD, MHSc, Aperio: Advisor/Consultant.

SARS‐CoV‐2 reinfection across a spectrum of immunological states

Purpose

Several cases of symptomatic reinfection with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) after full recovery from a prior episode have been reported. As reinfection has become an increasingly common phenomenon, an improved understanding of the risk factors for reinfection and the character and duration of the serological responses to infection and vaccination is critical for managing the coronavirus disease 2019 (COVID‐19) pandemic.

Methods

We described four cases of SARS‐CoV‐2 reinfection in individuals representing a spectrum of healthy and immunocompromised states, including (1) a healthy 41‐year‐old pediatrician, (2) an immunocompromised 31‐year‐old with granulomatosis with polyangiitis, (3) a healthy 26‐year‐old pregnant woman, and (4) a 50‐year‐old with hypertension and hyperlipidemia. We performed confirmatory quantitative reverse transcription‐polymerase chain reaction and qualitative immunoglobulin M and quantitative IgG testing on all available patient samples to confirm the presence of infection and serological response to infection.

Results

Our analysis showed that patients 1 and 2, a healthy and an immunocompromised patient, both failed to mount a robust serologic response to the initial infection. In contrast, patients 3 and 4, with minimal comorbid disease, both mounted a strong serological response to their initial infection, but were still susceptible to reinfection.

Conclusion

Repeat episodes of COVID‐19 are capable of occurring in patients regardless of the presence of known risk factors for infection or level of serological response to infection, although this did not trigger critical illness in any instance.

Non-diphtheriae Corynebacterium species are associated with decreased risk of pneumococcal colonization during infancy

Streptococcus pneumoniae (pneumococcus) is a leading cause of severe infections among children and adults. Interactions between commensal microbes in the upper respiratory tract and S. pneumoniae are poorly described. In this study, we sought to identify interspecies interactions that modify the risk of S. pneumoniae colonization during infancy and to describe development of the upper respiratory microbiome during infancy in a sub-Saharan African setting. We collected nasopharyngeal swabs monthly (0-6 months of age) or bimonthly (6-12 months of age) from 179 mother-infant dyads in Botswana. We used 16S ribosomal RNA gene sequencing to characterize the nasopharyngeal microbiome and identified S. pneumoniae colonization using a species-specific PCR assay. We detect S. pneumoniae colonization in 144 (80%) infants at a median age of 71 days and identify a strong negative association between the relative abundance of the bacterial genera Corynebacterium within the infant nasopharyngeal microbiome and the risk of S. pneumoniae colonization. Using in vitro cultivation experiments, we demonstrate growth inhibition of S. pneumoniae by secreted factors from strains of several Corynebacterium species isolated from these infants. Finally, we demonstrate that antibiotic exposures and the winter season are associated with a decline in the relative abundance of Corynebacterium within the nasopharyngeal microbiome, while breastfeeding is associated with an increase in the Corynebacterium relative abundance. Our findings provide novel insights into the interspecies interactions that contribute to colonization resistance to S. pneumoniae and suggest that the nasopharyngeal microbiome may be a previously unrecognized mechanism by which environmental factors influence the risk of pneumococcal infections during childhood. Moreover, this work lays the foundation for future studies seeking to use targeted manipulation of the nasopharyngeal microbiome to prevent infections caused by S. pneumoniae.

Envisioning Future UTI Diagnostics

Urinary tract infections (UTIs) are among the most common bacterial infections in the United States and are a major driver of antibiotic use - both appropriate and inappropriate - across healthcare settings. UTI treatment has become complex due to antibacterial resistance; one quarter of urinary tract isolates of Escherichia coli in the United States in 2017 were resistant to fluoroquinolones and one third to trimethoprimsulfamethoxazole (1), agents with historically predictable activity against E. coli. As a result, more broad-spectrum antibiotics are being used to treat UTIs, contributing to selection of further antibiotic resistance.

Low utilisation of bronchoscopy to assess COVID-19 respiratory infection: a multicenter experience

Objective

For the diagnosis of COVID-19, the yield of nasopharyngeal (NP) swabs is unclear, and bronchoalveolar lavage (BAL) is obtained to confirm the diagnosis. We assessed the utilisation of bronchoscopy for COVID-19 diagnosis in a multicenter study and compared the diagnostic yield of BAL versus NP swabs.

Methods

This retrospective study included all patients who were admitted with clinical presentation concerning for COVID-19 and underwent BAL from 1 March to 31 July 2020 at four tertiary care centres in North America. We also compared concordance of BAL with NP swabs for diagnosis of COVID-19 infection.

Results

Fifty-three patients, with clinical suspicion for COVID-19 and admitted for respiratory failure, underwent bronchoscopy to collect BAL for SARS-CoV-2 testing. During the same period, 2039 bronchoscopies were performed on patients not infected with COVID-19. Of 42 patients with NP swabs and BAL collected within ≤7 days, 1 was NP swab negative but positive by BAL for SARS-CoV-2 (n=1/42 (2.4%)). Across a wide array of testing platforms, the overall agreement between NP swabs and BAL results was 97.6% (95% CI: 93.0% to 100%) with Cohen’s k of 0.90 (95% CI: 0.69 to 1.00). The sensitivity, specificity, positive and negative predictive values of NP swabs compared with BAL were 83.3% (95% CI: 53.5% to 100%), 100%, 100% and 97.3% (95% CI: 92.1% to 100%), respectively.

Conclusions

BAL was used infrequently to assess COVID-19 in busy institutions. NP swabs have a high concordance with BAL for COVID-19 testing, but negative NP swabs should be confirmed with BAL when clinical suspicion is high.

782. Clostridioides difficile environmental contamination in hospitalized patients with diarrhea: a pilot study

Background

The relative contribution of Clostridioides difficile colonization or infection in contamination of the hospital environment is poorly understood.

Methods

We performed a prospective cohort study of patients with diarrhea who were tested for C. difficile infection via PCR and enzyme immunoassay (EIA) to compare C. difficile environmental contamination by test result. Patients were stratified into one of three cohorts: PCR-, PCR+/EIA+ or PCR+/EIA-. Environmental microbiological samples were taken within 24 hours of C. difficile cultures and again for two successive days for a total of three days. Patients were excluded if they had C. difficile infection in the past 6-weeks. Microbiological samples of surfaces were obtained with pre-moistened cellulose sponges from three locations (bathroom, adjacent to bed, and care areas) and processed using the stomacher technique. Ribotyping was completed on a subset of stool and environmental samples to measure concordance of isolates. CFU and recovery rates between arms were compared with a global ANOVA followed by pairwise comparisons using a Bonferroni adjustment.

Results

We enrolled 41 patients between November 2019 and March 2020. 7 patients were PCR+/EIA+, 8 were PCR+/EIA- and 26 were PCR- (Table 1). A total of 347 individual and 116 room samples were obtained. PCR+/EIA+ patient rooms had a higher average room burden (435.6 CFU (95%CI: 178.0-694.0)) compared to PCR+/EIA- (83.5 (-9.1-175.0), p&lt; 0.01) and PCR- rooms (17.1 (1.2-33.0), p&lt; 0.01); PCR+/EIA- and PCR- rooms were similar (p=0.83). PCR+/EIA+ patient rooms had a higher recovery rate (61%) compared to PCR+/EIA- (36%, p=0.64), although not statistically significant, and PCR- rooms (16%, p&lt; 0.01); PCR+/EIA- had a similar recovery rate to PCR- rooms (p=0.14) (Table 2). Of the rooms with both patient and environmental isolates, 79% of patient isolates had a concordant isolate recovered in the environment.

Table 1

Conclusion

The amount of environmental contamination of PCR+/EIA+ patients was higher than both PCR+/EIA- and PCR- patients, however, the recovery rate of PCR+/EIA+ patients was similar to PCR+/EIA- patients. Subsequent larger trials are needed to expand on this pilot data to determine the difference, if any, between environmental contamination levels of these patient populations.

Disclosures

David J. Weber, MD, MPH, PDI (Consultant)

Environmental and Aerosolized Severe Acute Respiratory Syndrome Coronavirus 2 Among Hospitalized Coronavirus Disease 2019 Patients

During April and May 2020, we studied 20 patients hospitalized with coronavirus disease 2019 (COVID-19), their hospital rooms (fomites and aerosols), and their close contacts for molecular and culture evidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Among >400 samples, we found molecular evidence of virus in most sample types, especially the nasopharyngeal (NP), saliva, and fecal samples, but the prevalence of molecular positivity among fomites and aerosols was low. The agreement between NP swab and saliva positivity was high (89.5%; κ = 0.79). Two NP swabs collected from patients on days 1 and 7 post-symptom onset had evidence of infectious virus (2 passages over 14 days in Vero E6 cells). In summary, the low molecular prevalence and lack of viable SARS-CoV-2 virus in fomites and air samples implied low nosocomial risk of SARS-CoV-2 transmission through inanimate objects or aerosols.

Assessment of an Online Tool to Simulate the Effect of Pooled Testing for SARS-CoV-2 Detection in Asymptomatic and Symptomatic Populations

This diagnostic study describes an online tool created with actual severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus copy number data to help policy makers understand how pooled testing compares with single-sample testing in different populations.

Implementation of a Pooled Surveillance Testing Program for Asymptomatic SARS-CoV-2 Infections on a College Campus - Duke University, Durham, North Carolina, August 2-October 11, 2020

On university campuses and in similar congregate environments, surveillance testing of asymptomatic persons is a critical strategy (1,2) for preventing transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). All students at Duke University, a private research university in Durham, North Carolina, signed the Duke Compact (3), agreeing to observe mandatory masking, social distancing, and participation in entry and surveillance testing. The university implemented a five-to-one pooled testing program for SARS-CoV-2 using a quantitative, in-house, laboratory-developed, real-time reverse transcription-polymerase chain reaction (RT-PCR) test (4,5). Pooling of specimens to enable large-scale testing while minimizing use of reagents was pioneered during the human immunodeficiency virus pandemic (6). A similar methodology was adapted for Duke University's asymptomatic testing program. The baseline SARS-CoV-2 testing plan was to distribute tests geospatially and temporally across on- and off-campus student populations. By September 20, 2020, asymptomatic testing was scaled up to testing targets, which include testing for residential undergraduates twice weekly, off-campus undergraduates one to two times per week, and graduate students approximately once weekly. In addition, in response to newly identified positive test results, testing was focused in locations or within cohorts where data suggested an increased risk for transmission. Scale-up over 4 weeks entailed redeploying staff members to prepare 15 campus testing sites for specimen collection, developing information management tools, and repurposing laboratory automation to establish an asymptomatic surveillance system. During August 2-October 11, 68,913 specimens from 10,265 graduate and undergraduate students were tested. Eighty-four specimens were positive for SARS-CoV-2, and 51% were among persons with no symptoms. Testing as a result of contact tracing identified 27.4% of infections. A combination of risk-reduction strategies and frequent surveillance testing likely contributed to a prolonged period of low transmission on campus. These findings highlight the importance of combined testing and contact tracing strategies beyond symptomatic testing, in association with other preventive measures. Pooled testing balances resource availability with supply-chain disruptions, high throughput with high sensitivity, and rapid turnaround with an acceptable workload.

84. Evaluation of the NHSN Standardized Infection Ratio (SIR) Risk Adjustment for HO-CDI in Oncology and ICU Patients in General Acute Care Hospitals

Background

The NHSN healthcare-facility onset Clostridioides difficile infection (CDI) standardized infection ratio (SIR) is used to compare hospital quality and set hospital reimbursement but inadequate risk adjustment could penalize hospitals unnecessarily. We hypothesized that general hospitals with large oncology and/or ICU populations were not fully adjusted in the 2015 NHSN acute care hospital CDI Laboratory-Identified (LabID) event prediction model and SIRs would be affected.

Methods

We validated a negative binomial regression HO-CDI event prediction model identical to the 2015 published model and used FY2016 data from eight general hospitals in California to test our hypothesis. We compared HO-CDI events and SIR values, with and without oncology/hematopoietic stem cell transplant or ICU unit events, patient-days, admissions, bed counts, and adjustment parameters included.

Results

Seven major teaching and one nonteaching general acute care hospitals were included (see Table). Eight had oncology/hematopoietic stem cell transplant units; seven had ≥43 ICU beds (median: 134; interquartile range [IQR]: 84–161). The median facility unmodified FacWideIn SIR was 1.23 [IQR: 1.15, 1.29]. Removal of oncology unit data resulted in a 15% median facility decrease in HO-CDI events (IQR: 14%, 21%) and −8% median facility decrease in SIR (IQR: −2%, −14%). Removal of ICU unit data resulted in a 22% median facility decrease in HO-CDI events (IQR: 16%, 26%) and 97% median facility increase in SIR at each facility (IQR: 78%, 105%).

Conclusion

The ICU bed adjustment in the 2015 NHSN SIR is a powerful correction that fully adjusted for ICU HO-CDI events at all hospitals in the study. However, the lack of risk adjustment for oncology/hematopoietic stem cell transplant unit HO-CDI events suggests that the current model unfairly penalizes general acute facilities, many of which also provide specialized oncologic care. Thus, the model needs to be re-adjusted to account for this important specialty care population in general acute care facilities.

Disclosures

All Authors: No reported Disclosures.

839. Effect of Clostridioides difficile (C. difficile) Toxin Test Reporting on Clinical Treatment and Outcomes of Toxin-Negative PCR-Positive Patients at Five California Hospitals

Background

Guidelines support the use of toxin tests after C. difficile antigen detection or nucleic acid amplification tests (e.g., PCR) to help clinicians distinguish colonization from infection and reduce overdiagnosis but the safety of toxin-based diagnostic approaches remains controversial.

Methods

Five California hospitals monitored hospitalized adults with C. difficile testing before and after operational changes to reduce test-related overdiagnosis (2016–2018). Four added a toxin test to an existing GDH antigen/PCR-based approach and/or changed reporting to encourage the use of toxin results for clinical decision-making (i.e.,“toxin-dominant reporting”). One used the same test (toxin only) and reporting strategy throughout. All used a standardized tool to document clinical outcomes and treatment four days after testing (i.e., Day 5).

Results

In total, 1,034 patients had a Day 5 assessment with PCR-dominant reporting (pre-operational changes); 2,511 patients had a Day 5 assessment with toxin-dominant reporting (post-operational changes and single facility with no test change). Fewer Toxin-negative/PCR-positive (Toxin−/PCR+) patients received treatment with toxin-dominant reporting (median change: −52.1% [interquartile range (IQR): −35.1%, −69.1%]; aggregate P < 0.001). Day 5 outcomes were similar or better with toxin-dominant reporting despite less treatment. Patient discharge rates and in hospital diarrheal recovery was greater in the subset of Toxin−/PCR+ patients during the toxin-dominant reporting period: median discharge rate change = 8.8% [IQR: 1.5%, 11.9%] (aggregate P = 0.04); median diarrheal recovery rate change = 11.8% [IQR: 8.8%, 18.2%] (aggregate P = 0.018).

Conclusion

In a 5-center study, toxin-dominant test result reporting decreased anti-C. difficile treatment and improved discharge rates and diarrheal recovery in Toxin−/PCR+ patients. More work is needed to determine the rate of C. difficile-related adverse events in Toxin−/PCR+ patients.

Disclosures

All Authors: No reported Disclosures.

Clinical Metagenomic Sequencing for Diagnosis of Meningitis and Encephalitis

BACKGROUND

Metagenomic next-generation sequencing (NGS) of cerebrospinal fluid (CSF) has the potential to identify a broad range of pathogens in a single test.

METHODS

In a 1-year, multicenter, prospective study, we investigated the usefulness of metagenomic NGS of CSF for the diagnosis of infectious meningitis and encephalitis in hospitalized patients. All positive tests for pathogens on metagenomic NGS were confirmed by orthogonal laboratory testing. Physician feedback was elicited by teleconferences with a clinical microbial sequencing board and by surveys. Clinical effect was evaluated by retrospective chart review.

RESULTS

We enrolled 204 pediatric and adult patients at eight hospitals. Patients were severely ill: 48.5% had been admitted to the intensive care unit, and the 30-day mortality among all study patients was 11.3%. A total of 58 infections of the nervous system were diagnosed in 57 patients (27.9%). Among these 58 infections, metagenomic NGS identified 13 (22%) that were not identified by clinical testing at the source hospital. Among the remaining 45 infections (78%), metagenomic NGS made concurrent diagnoses in 19. Of the 26 infections not identified by metagenomic NGS, 11 were diagnosed by serologic testing only, 7 were diagnosed from tissue samples other than CSF, and 8 were negative on metagenomic NGS owing to low titers of pathogens in CSF. A total of 8 of 13 diagnoses made solely by metagenomic NGS had a likely clinical effect, with 7 of 13 guiding treatment.

CONCLUSIONS

Routine microbiologic testing is often insufficient to detect all neuroinvasive pathogens. In this study, metagenomic NGS of CSF obtained from patients with meningitis or encephalitis improved diagnosis of neurologic infections and provided actionable information in some cases. (Funded by the National Institutes of Health and others; PDAID ClinicalTrials.gov number, NCT02910037.).

Advances in the diagnosis and treatment of Clostridium difficile infections

Clostridium difficile is a leading cause of antibiotic-associated diarrhea worldwide. The diagnosis of C. difficile infection (CDI) requires both clinical manifestations and a positive laboratory test for C. difficile and/or its toxins. While antibiotic therapy is the treatment of choice for CDI, there are relatively few classes of effective antibiotics currently available. Therefore, the development of novel antibiotics and/or alternative treatment strategies for CDI has received a great deal of attention in recent years. A number of emerging agents such as cadazolid, surotomycin, ridinilazole, and bezlotoxumab have demonstrated activity against C. difficile; some of these have been approved for limited clinical use and some are in clinical trials. In addition, other approaches such as early and accurate diagnosis of CDI as well as disease prevention are important for clinical management. While the toxigenic culture and the cell cytotoxicity neutralization assay are still recognized as the gold standard for the diagnosis of CDI, new diagnostic approaches such as nucleic acid amplification methods have become available. In this review, we will discuss both current and emerging diagnostic and therapeutic modalities for CDI.

Overdiagnosis of Clostridium difficile Infection in the Molecular Test Era

IMPORTANCE

Clostridium difficile is a major cause of health care-associated infection, but disagreement between diagnostic tests is an ongoing barrier to clinical decision making and public health reporting. Molecular tests are increasingly used to diagnose C difficile infection (CDI), but many molecular test-positive patients lack toxins that historically defined disease, making it unclear if they need treatment.

OBJECTIVE

To determine the natural history and need for treatment of patients who are toxin immunoassay negative and polymerase chain reaction (PCR) positive (Tox-/PCR+) for CDI.

DESIGN, SETTING, AND PARTICIPANTS

Prospective observational cohort study at a single academic medical center among 1416 hospitalized adults tested for C difficile toxins 72 hours or longer after admission between December 1, 2010, and October 20, 2012. The analysis was conducted in stages with revisions from April 27, 2013, to January 13, 2015.

MAIN OUTCOMES AND MEASURES

Patients undergoing C difficile testing were grouped by US Food and Drug Administration-approved toxin and PCR tests as Tox+/PCR+, Tox-/PCR+, or Tox-/PCR-. Toxin results were reported clinically. Polymerase chain reaction results were not reported. The main study outcomes were duration of diarrhea during up to 14 days of treatment, rate of CDI-related complications (ie, colectomy, megacolon, or intensive care unit care) and CDI-related death within 30 days.

RESULTS

Twenty-one percent (293 of 1416) of hospitalized adults tested for C difficile were positive by PCR, but 44.7% (131 of 293) had toxins detected by the clinical toxin test. At baseline, Tox-/PCR+ patients had lower C difficile bacterial load and less antibiotic exposure, fecal inflammation, and diarrhea than Tox+/PCR+ patients (P < .001 for all). The median duration of diarrhea was shorter in Tox-/PCR+ patients (2 days; interquartile range, 1-4 days) than in Tox+/PCR+ patients (3 days; interquartile range, 1-6 days) (P = .003) and was similar to that in Tox-/PCR- patients (2 days; interquartile range, 1-3 days), despite minimal empirical treatment of Tox-/PCR+ patients. No CDI-related complications occurred in Tox-/PCR+ patients vs 10 complications in Tox+/PCR+ patients (0% vs 7.6%, P < .001). One Tox-/PCR+ patient had recurrent CDI as a contributing factor to death within 30 days vs 11 CDI-related deaths in Tox+/PCR+ patients (0.6% vs 8.4%, P = .001).

CONCLUSIONS AND RELEVANCE

Among hospitalized adults with suspected CDI, virtually all CDI-related complications and deaths occurred in patients with positive toxin immunoassay test results. Patients with a positive molecular test result and a negative toxin immunoassay test result had outcomes that were comparable to patients without C difficile by either method. Exclusive reliance on molecular tests for CDI diagnosis without tests for toxins or host response is likely to result in overdiagnosis, overtreatment, and increased health care costs.

Neutrophils: Another Case of Wrongful Conviction?

Oxygen depletion by the neutrophil respiratory burst induces a protective stress response in mucosal epithelial cells.

Hydrogen Fuels Cells in the Gut

Salmonella uses the hydrogen produced by resident gut microbes to get a boost in early infection.

The Gut Is No Place for Freedom of Expression

Histone deacetylase 3 regulates epithelial cell responses to bacteria in the gut.

Neutrophils Block Bacterial Flood in Gut Infection

Neutrophils form a protective cast around commensal bacteria to limit mucosal exposure during intestinal infections.

Good and Bad Bacteria Fight for Iron in the Gut

A probiotic strain, E. coli Nissle 1917, uses multiple iron transporters to outcompete Salmonella in the inflamed gut.

Fish Oil Cools the Inflammasome

Omega-3 fatty acids directly inhibit the NLRP3 inflammasome in vitro and decrease tissue inflammation and insulin resistance in mice.

One More Reason to Love Mother’s Milk

Breast milk–derived sodium nitrate provides an exogenous source of nitric oxide that protects against ischemia in necrotizing enterocolitis.

Microbes Hold the Key to Metformin-Induced Longevity

Metformin-induced alterations in microbial folate metabolism mediate life-span extension in Caenorhabditis elegans .

Mast Cells Help Bacteria Hang Out After the Party

Mast cell-derived IL-10 shifts the bladder towards immune tolerance and limits adaptive immunity to pathogens.

Evaluation of Clostridium difficile fecal load and limit of detection during a prospective comparison of two molecular tests, the illumigene C. difficile and Xpert C. difficile/Epi tests

In a large prospective comparison, the illumigene test detected Clostridium difficile in 98% of toxin-positive and 58% of toxin-negative samples confirmed positive by other methods. The Xpert was uniformly sensitive. Most samples with discrepant results had C. difficile concentrations below the illumigene limit of detection. The significance of low-level C. difficile detection needs investigation.

Outcomes in patients tested for Clostridium difficile toxins

Clostridium difficile testing is shifting from toxin detection to C. difficile detection. Yet, up to 60% of patients with C. difficile by culture test negative for toxins and it is unclear whether they are infected or carriers. We reviewed medical records for 7046 inpatients with a C. difficile toxin test from 2005 to 2009 to determine the duration of diarrhea and rate of complications and mortality among toxin-positive (toxin+) and toxin- patients. Overall, toxin- patients had less severe diarrhea, fewer diarrhea days, and lower mortality (P < 0.001, all comparisons) than toxin+ patients. One toxin- patient (n = 1/6121; 0.02%) was diagnosed with pseudomembranous colitis, but there were no complications such as megacolon or colectomy for fulminant CDI among toxin- patients. These data suggest that C. difficile-attributable complications are rare among patients testing negative for C. difficile toxins. More studies are needed to evaluate the clinical significance of C. difficile detection in toxin- patients.

Nosocomial diarrhea: evaluation and treatment of causes other than Clostridium difficile

Diarrhea is common among hospitalized patients but the causes are distinct from those of diarrhea in the community. We review existing data about the epidemiology of nosocomial diarrhea and summarize recent progress in understanding the mechanisms of diarrhea. Clinicians should recognize that most cases of nosocomial diarrhea have a noninfectious etiology, including medications, underlying illness, and enteral feeding. Apart from Clostridium difficile, the frequency of infectious causes such as norovirus and toxigenic strains of Clostridium perfringens, Klebsiella oxytoca, Staphylococcus aureus, and Bacteroides fragilis remains largely undefined and test availability is limited. Here we provide a practical approach to the evaluation and management of nosocomial diarrhea when tests for C. difficile are negative.

Evaluation of Escherichia coli cell response to antibiotic treatment by use of Raman spectroscopy with laser tweezers

Laser tweezers Raman spectroscopy was used to detect the cellular response of Escherichia coli cells to penicillin G-streptomycin and cefazolin. Time-dependent intensity changes of several Raman peaks at 729, 1,245, and 1,660 cm(-1) enabled untreated cells and cells treated with the different antibiotic drugs to be distinguished.

Performance of diagnostic tests to detect respiratory viruses in older adults

The performance of 4 laboratory methods for diagnosis of viral respiratory tract infections (RTI) in older adults was evaluated. Seventy-four nasopharyngeal (NP) swab specimens were obtained from 60 patients with RTI at a long-term care facility over 2 respiratory seasons. Sixteen specimens were positive for a respiratory virus by at least 1 method. Multiplex reverse transcriptase polymerase chain reaction (RT-PCR) by the Luminex xTAG Respiratory Viral Panel (RVP) detected 16 (100%) of the positive specimens, RVP of 24-h culture supernatant detected 8 (50%), direct fluorescent antibody testing detected 4 (25%), rapid culture detected 2 (12.5%), and rapid antigen testing detected none. For a comparison group, RVP was performed on NP swabs from 20 outpatient children with RTI. The mean fluorescence intensity by RVP was significantly lower for positive adult patients than pediatric patients (P = 0.0373). Our data suggest that older adult patients shed lower titers of viruses, necessitating a highly sensitive assay such as RT-PCR to reliably detect respiratory viral pathogens.

Respiratory syncytial virus outbreak in a long-term care facility detected using reverse transcriptase polymerase chain reaction: an argument for real-time detection methods

OBJECTIVES: To report an outbreak of respiratory synctyial virus (RSV) in a long‐term care facility (LTCF) during ongoing routine respiratory illness surveillance.

DESIGN: Rapid antigen testing, viral culture, direct fluorescent antibody (DFA) testing, and reverse transcriptase polymerase chain reaction (RT‐PCR) testing for up to 15 viruses in symptomatic residents and chart review.

SETTING: A 120‐bed LTCF.

MEASUREMENTS: Comparison of rapid antigen testing, respiratory viral cultures, and DFA testing and RT‐PCR in residents with symptoms of a respiratory tract infection.

RESULTS: Twenty‐two of 52 residents developed symptoms of a respiratory tract infection between January 29, 2008, and February 26, 2008. RSV was detected using RT‐PCR in seven (32%) of the 22 cases. None of the seven cases had positive RSV rapid antigen testing, and only two had positive culture or DFA results. This outbreak occurred during a time when state wide RSV rates were rapidly declining. One patient was admitted to the hospital during the infection and subsequently died.

CONCLUSION: RSV may cause outbreaks in LTCFs that traditional diagnostic methods do not detect. RT‐PCR can provide a more timely and accurate diagnosis of outbreaks, which allows for early symptomatic treatment, rational use of antibiotics, and improved infection control.

Assessment of the Utility of Viral Culture of Cerebrospinal Fluid

Nucleic acid amplification testing is the preferred method to detect enteroviruses and Herpesviridae in cerebrospinal fluid, but clinicians still request viral culture. Review of 22,394 viral cultures of cerebrospinal fluid samples found that <0.1% recovered nonenterovirus, non-Herpesviridae species, suggesting that, when nucleic acid amplification testing is performed, viral culture may have no additional benefit.

Laboratory use in Ghana: physician perception and practice

Clinical diagnosis of infectious diseases in Africa has been associated with increased misdiagnosis and mortality, but when laboratory testing is available, it remains underused. We retrospectively compared infectious diagnoses, test results, anti-microbial use, and patient cost with laboratory and physician surveys at a teaching hospital in Ghana to evaluate the potential barriers to laboratory use and financial impact for patients. Laboratory capacity was high, but physician survey results and objective data indicated a reliance on clinical judgment and empirical therapy. For the study period, 9-15% of malaria diagnoses, 34-43% of urinary tract infections (UTIs), and 62% of meningitis cases were supported by abnormal laboratory results. For the same period, 0.82-2.09 units of antibiotics were consumed per patient day, and patient cost for antibiotics was 4.8-21.6 times that of laboratory testing. Physician perception regarding the value of diagnostic testing is potentially a major barrier to laboratory use, resulting in empiricism, disproportionate anti-microbial administration, and cost to patients.

The role of 16S rRNA gene sequencing in identification of microorganisms misidentified by conventional methods

Traditional methods for microbial identification require the recognition of differences in morphology, growth, enzymatic activity, and metabolism to define genera and species. Full and partial 16S rRNA gene sequencing methods have emerged as useful tools for identifying phenotypically aberrant microorganisms. We report on three bacterial blood isolates from three different College of American Pathologists-certified laboratories that were referred to ARUP Laboratories for definitive identification. Because phenotypic identification suggested unusual organisms not typically associated with the submitted clinical diagnosis, consultation with the Medical Director was sought and further testing was performed including partial 16S rRNA gene sequencing. All three patients had endocarditis, and conventional methods identified isolates from patients A, B, and C as a Facklamia sp., Eubacterium tenue, and a Bifidobacterium sp. 16S rRNA gene sequencing identified the isolates as Enterococcus faecalis, Cardiobacterium valvarum, and Streptococcus mutans, respectively. We conclude that the initial identifications of these three isolates were erroneous, may have misled clinicians, and potentially impacted patient care. 16S rRNA gene sequencing is a more objective identification tool, unaffected by phenotypic variation or technologist bias, and has the potential to reduce laboratory errors.