Kevan L. Hanson

Diagnostic Performance of Rapid Diagnostic Tests versus Blood Smears for Malaria in US Clinical Practice

BACKGROUND Approximately 4 million US travelers to developing countries are ill enough to seek health care, with 1500 malaria cases reported in the United States annually. The diagnosis of malaria is frequently delayed because of the time required to prepare malaria blood films and lack of technical expertise. An easy, reliable rapid diagnostic test (RDT) with high sensitivity and negative predictive value (NPV), particularly for Plasmodium falciparum, would be clinically useful. The objective of this study was to determine the diagnostic performance of a RDT approved by the US Food and Drug Administration compared with traditional thick and thin blood smears for malaria diagnosis. METHODS This prospective study tested 852 consecutive blood samples that underwent thick and thin smears and blinded malaria RDTs at 3 hospital laboratories during 2003-2006. Polymerase chain reaction verified positive test results and discordant results. RESULTS Malaria was noted in 95 (11%) of the 852 samples. The RDT had superior performance than the standard Giemsa thick blood smear (p = .003). The RDTs sensitivity for all malaria was 97% (92 of 95 samples), compared with 85% (81 of 95) for the blood smear, and the RDT had a superior NPV of 99.6%, compared with 98.2% for the blood smear (p = .001). The P. falciparum performance was excellent, with 100% rapid test sensitivity, compared with only 88% (65 of 74) by blood smear (p = .003). CONCLUSIONS This operational study demonstrates that the US Food and Drug Administration-approved RDT for malaria is superior to a single set of blood smears performed under routine US clinical laboratory conditions. The most valuable clinical role of the RDT is in the rapid diagnosis or the exclusion of P. falciparum malaria, which is particularly useful in outpatient settings when evaluating febrile travelers.

Use of an Enzyme Immunoassay Does Not Eliminate the Need To Analyze Multiple Stool Specimens for Sensitive Detection of Giardia lamblia

ABSTRACT The relative sensitivities of a commercially available enzyme immunoassay (EIA) (ProSpecT Giardia; Alexon-Trend Inc., Ramsey, Minn.) and conventional ovum-and-parasite (O&P) examination for the detection of Giardia lamblia in preserved stool specimens were determined. Paired stool samples collected independently within a 7-day period from 103 patients were analyzed by both methods. A total of 54 specimens from 30 patients (18 asymptomatically infected with G. lamblia and 12 with symptoms consistent with intestinal giardiasis) were determined to be positive for G. lamblia, of which 48 (88.9%) were positive by microscopy and 52 (96.3%) were positive by EIA. Both specimens submitted were positive for G. lamblia by O&P examination for 66.7% (20 of 30) of the positive patients; for 26.7% (8 of 30) a single specimen was positive by O&P examination, and for 6.7% (2 of 30) of those determined to be infected with G. lamblia, both samples were negative by microscopy. The sensitivity of conventional O&P examination was somewhat higher in symptomatically infected individuals, with 75% (9 of 12) of patients in this category havingG. lamblia detected in both samples, compared with 61% (11 of 18) of asymptomatic patients. A total of 24 positive patients (80%) had G. lamblia antigen detected by EIA in both submitted samples, 4 positive patients (13.3%) had one specimen positive by EIA, and the EIA was negative in both specimens from 2 infected individuals (6.5%), the sensitivity of EIA was substantially equivalent in asymptomatic and symptomatic individuals (77 versus 83% of patients with positive results on both specimens). Although the sensitivity of EIA for the detection of G. lamblia on a single stool specimen was somewhat higher than that of conventional O&P examination in symptomatic patients (83 versus 75%), in asymptomatic patients (77 versus 61%), and overall (80 versus 67%), examination of two specimens by either EIA or microscopy was necessary to achieve a diagnostic sensitivity of greater than 90%.

Comparison of 2 Blood Culture Media Shows Significant Differences in Bacterial Recovery for Patients on Antimicrobial Therapy

BACKGROUND Antimicrobial removal devices in blood culture media are designed to remove antibiotics from the blood culture solution, thereby facilitating bacterial growth. How well these devices function clinically has not been established. METHODS All blood drawn for culture from adult inpatients and emergency department visitors in a level I trauma center was placed in paired BACTEC Plus and BacT/Alert FAN culture media and studied simultaneously, consecutively, and prospectively between 1 February and 30 September 2011. All cultures were processed per standard laboratory protocols. RESULTS Of 9395 total cultures collected, 1219 (13%) were positive, 831 were included, and 524 (33%) contained pathogens. BACTEC had a 4.5-hour faster detection time (P < .0001), and isolated exclusively 182 of 524 (35%; P < .001) pathogens, 136 of 345 (39%) of the gram-positive cocci (P < .001), 48 of 175 (27%; P = .02) of the gram-negative rods, 101 of 195 (52%) of Staphylococcus aureus (P < .001), and 59 of 120 (49%; P = .004) septic events. If active antibiotics had been dosed 0-4 or 4-48 hours prior to culture collection, the odds of that culture growing in BACTEC were 4.8- and 5.2-fold greater, respectively, than of growing in BacT/Alert (P < .0001). Both were equivalent in the recovery of yeast and when no antimicrobials were dosed. CONCLUSIONS BACTEC media has faster time to detection and increased bacterial recovery over the BacT/Alert media in the following categories: overall growth, pathogens, septic events, gram-positive cocci, gram-negative rods, Staphylococcus aureus, and cultures where antimicrobials were dosed up to 48 hours before culture collection.

Evaluation Of Malaria Screening In Newly Arrived Refugees To The United States By Microscopy And Rapid Antigen Capture Enzyme Assay

Before an empiric malaria treatment program, >60% of Liberian refugees had malaria on arrival to Minnesota. We compared microscopy with rapid antigen testing for detecting asymptomatic parasitemia. Nine of 103 (8.7%) had malaria by polymerase chain reaction (blood smear and rapid testing had a sensitivity of 22%). The empiric treatment program has decreased the rate of imported asymptomatic malaria. Blood film and rapid antigen testing are poor screening tests.

Evaluation of an Automated Liquid-Handling System (Tecan Genesis RSP 100) in the Abbott LCx Assay for Chlamydia trachomatis

ABSTRACT The present study investigated the feasibility of automating the specimen-pipetting component of sample preparation in the LCx Chlamydia assay (LCx-CT assay; Abbott Laboratories, Chicago, Ill.) by using a commercially available liquid-handling system (Tecan Genesis RSP100; Tecan Inc., Research Triangle Park, N.C.). The Tecan instrument proved to be comparable in both precision and accuracy to a manual multipipettor (Eppendorf model 4850; Eppendorf Scientific, Westbury, N.Y.). The Tecan instrument was extensively checked for evidence of specimen-to-specimen transfer, and no level of contamination sufficient to generate a signal above the background in the LCx-CT assay was detected. Finally, pipetting speed was significantly improved by using the Tecan instrument. A mean time of 2.5 min was required to pipette a complete LCx-CT assay carousel (20 samples and 4 controls) with the Tecan instrument, whereas 8.4 min was required to pipette a comparable number of samples manually (P < 0.001).

Delayed incubation of blood culture bottles: Effect on recovery rate of streptococcus pneumoniae and haemophilus influenzae type B

This study investigated the effects of incubation delay on the rate of recovery of common pediatric pathogens from blood culture bottles. Known concentrations of Streptococcus pneumoniae and Haemophilus influenzae type b (three isolates each) were inoculated into BACTEC NR-6A bottles with 1.0 mL of donor blood. Bottles were subjected to a time delay (zero to six hours) before incubation. The BACTEC NR-660° was used for incubation and measurement of positive conversion. Data were analyzed using X2 analysis, Fishers exact test, logistic regression, and multiple logistic regression, with P < 0.05 considered significant. Immediate incubation yielded positive blood cultures in 88 of 100 and 65 of 70 bottles containing S. pneumoniae and H. influenzae type b, respectively, in the concentration range 1.0 to 9.99 colonyforming units per milliliter (CFU/ml). For each organism, this was the minimal range required to produce a positive culture (P < 0.0001). Bottles inoculated with 1 ml of blood containing organisms in the range of 1.0 to 9.99 CFU/ml were then subjected to incubation delay. The recovery rate of S. pneumoniae significantly (P = 0.0003) decreased from a two-hour delay (57 of 60; 95%) to a three-hour delay (42 of 60; 70%). No significant change in recovery rate was seen in bottles inoculated with H. influenzae type b subjected to similar delays. Delayed incubation (two to six hours) of bottles inoculated with 1.0 ml of blood containing organisms in a concentration range of 1.0 to 9.99 CFU/ml of blood significantly decreases the recovery rate of S. pneumoniae but has no effect on H. influenzae type b.

Performance of para-Pak Ultra ECOFIX compared with Para-Pak Ultra formalin/mercuric chloride-based polyvinyl alcohol for concentration and permanent stained smears of stool parasites.

ECOFIX is a mercury and formalin-free fecal preservative that can be used for concentration of stool specimens and preparation of permanently-stained slides. In this study, the standard two-vial ParaPak Ultra system was compared with ECOFIX Ultra for the detection of intestinal parasites. A total of 261 specimens in 92 sets (77 with 3 specimens, 15 with 2 specimens) were collected in ECOFIX, formalin, and low viscosity polyvinyl alcohol (LV-PVA). Concentrations were performed from ECOFIX using Hemo-De and saline and from formalin using ethyl acetate and formalin. To prepare permanently-stained smears, ECOSTAIN (a modification of Wheatleys trichrome stain) was used on ECOFIX material and Wheatleys trichrome stain was used on specimens preserved in PVA. A total of 157 protozoa and helminths were detected; 132 (84.1%) were recovered in formalin/PVA and 129 (82.2%) in ECOFIX. In permanently-stained smears, 139 protozoa were observed, 116 (83.5%) in PVA-preserved material and 117 (84.2%) in ECOFIX. Fecal concentration yielded 111 parasites (103 protozoa and 8 helminths), of which 98 (88.3%) were detected in formalin-fixed stool and 48 (43.2%) in ECOFIX. Significantly fewer ECOFIX-preserved concentrates were positive for Blastocystis hominis (35 versus 15, p-value <0.001) and Endolimax nana (19 versus 2, p-value <0.001). In conclusion, use of the ECOFIX Ultra collection device in combination with ECOSTAIN resulted in largely comparable recovery of enteric parasites to the conventional two-vial ParaPak Ultra system when both sedimentation-concentration and permanently stained smears were performed, and 2-3 specimens per patient were evaluated.

A Study of Results Generated Using the Abbott LCx-GC Assay Fails to Reveal a Performance-Based Rationale for the 2002 Level 1 Recall

To establish the effect of a quality control failure on the performance of the LCx-GC nucleic-acid amplification assay for Neisseria gonorrhoeae (Abbott Laboratories, Abbott Park, IL) in the field, we conducted a retrospective analysis comparing the clinical and analytic performance of the recalled lots with those not implicated in the recall. Our analysis revealed no statistically significant differences between recalled lots (n = 8,686 tests) and nonrecalled lots (n = 8,699 tests) with respect to multiple parameters of assay performance, including frequency distribution of patient results (P = .575), prevalence of indeterminate results (P = .245), mean positive control signals (P = .26), and within-run calibrator precision (P = .68). The LCx-GC systems lack of an electronic data storage and retrieval capability prevented assessment of the impact of the quality control failure on the clinical performance of recalled lots, such as the one described herein, from being conducted in real time.

Clinical decision making in the emergency department setting using rapid PCR: Results of the CLADE study group

Abstract Background Emergency Departments (ED) are challenged during influenza season by patients who present acutely during sporadic ED visits. ED management is largely empiric, often occurring without reliable diagnostics needed for targeted therapies, safe outpatient discharge, or hospital admissions. Objective To evaluate the impact of the influenza diagnosis on physician decision making during ED visits using the Cobas Liat® influenza A + B assay. Study design Prospective study assessing the impact of rapid (<30 min), reverse-transcriptase polymerase chain reaction (RT-PCR) influenza testing on physician decision making in the ED. Physician responses established pre-and post-diagnosis management courses which required confirmation via secondary documentation in the medical record. Changes in physician decision making were analyzed across four clinical touchpoints: (i) admission/discharge status, (ii) medical procedures, (iii) antiviral and antibiotic prescribing, and (iv) laboratory studies. Results An influenza diagnosis changed patient management courses, relative to empiric, pre-diagnosis plans, in in 61% of the cases resulting in cost savings of

Comparison of Simple and Rapid Methods for Identifying Enterococci Intrinsically Resistant to Vancomycin

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