New point of care test is highly specific but less sensitive for influenza virus A and B in children and adults

Practical Guidance for Clinical Microbiology Laboratories: Viruses Causing Acute Respiratory Tract Infections

Respiratory viral infections are associated with a wide range of acute syndromes and infectious disease processes in children and adults worldwide. Many viruses are implicated in these infections, and these viruses are spread largely via respiratory means between humans but also occasionally from animals to humans. This article is an American Society for Microbiology (ASM)-sponsored Practical Guidance for Clinical Microbiology (PGCM) document identifying best practices for diagnosis and characterization of viruses that cause acute respiratory infections and replaces the most recent prior version of the ASM-sponsored Cumitech 21 document, Laboratory Diagnosis of Viral Respiratory Disease, published in 1986. The scope of the original document was quite broad, with an emphasis on clinical diagnosis of a wide variety of infectious agents and laboratory focus on antigen detection and viral culture. The new PGCM document is designed to be used by laboratorians in a wide variety of diagnostic and public health microbiology/virology laboratory settings worldwide. The article provides guidance to a rapidly changing field of diagnostics and outlines the epidemiology and clinical impact of acute respiratory viral infections, including preferred methods of specimen collection and current methods for diagnosis and characterization of viral pathogens causing acute respiratory tract infections. Compared to the case in 1986, molecular techniques are now the preferred diagnostic approaches for the detection of acute respiratory viruses, and they allow for automation, high-throughput workflows, and near-patient testing. These changes require quality assurance programs to prevent laboratory contamination as well as strong preanalytical screening approaches to utilize laboratory resources appropriately. Appropriate guidance from laboratorians to stakeholders will allow for appropriate specimen collection, as well as correct test ordering that will quickly identify highly transmissible emerging pathogens.

An HRP-labeled lateral flow immunoassay for rapid simultaneous detection and differentiation of influenza A and B viruses

Rapid and sensitive diagnosis of influenza is urgently needed to address the limitations of low sensitivity associated with current rapid tests available for clinics and on-site monitoring. A novel horseradish peroxidase (HRP)-labeled lateral flow immunoassay strip (HRP-LFIA) for rapid simultaneous detection and differentiation of influenza A (INF A) and influenza B (INF B) viruses were developed. This immunoassay was based on the signal amplification by the HRP-catalyzed oxidation of 3, 3', 5, 5'-tetramethylbenzidine forming a colored insoluble product, which was proportional to the analyte concentration. Compared with conventional gold-colloidal based strips, an analytical sensitivity enhancement of more than one order of magnitude for thirteen INF virus isolates was observed. A total of 1487 swabs obtained from persons with influenza-like illnesses were tested for the presence of INF A and B viruses using real-time reverse transcription polymerase chain reaction (rRT-PCR) as the reference criterion. The overall sensitivities of HRP-LFIA were 77.5% (100/129) and 71.2% (116/163) for INF A and INF B, respectively. The overall specificities were 99.8% (1144/1146) and 99.8% (918/920), respectively. The nasopharyngeal sampling method yielded higher sensitivity rates of 90.2% (55/61) and 82.6% (71/86). In conclusion, this user-friendly assay could be a promising rapid detection method for rapid screening of INF A and INF B viruses.

Point-of-care cardiac troponin test accurately predicts heat stroke severity in rats

Heat stroke (HS) remains a significant public health concern. Despite the substantial threat posed by HS, there is still no field or clinical test of HS severity. We suggested previously that circulating cardiac troponin (cTnI) could serve as a robust biomarker of HS severity after heating. In the present study, we hypothesized that (cTnI) point-of-care test (ctPOC) could be used to predict severity and organ damage at the onset of HS. Conscious male Fischer 344 rats (n = 16) continuously monitored for heart rate (HR), blood pressure (BP), and core temperature (Tc) (radiotelemetry) were heated to maximum Tc (Tc,Max) of 41.9 ± 0.1°C and recovered undisturbed for 24 h at an ambient temperature of 20°C. Blood samples were taken at Tc,Max and 24 h after heat via submandibular bleed and analyzed on ctPOC test. POC cTnI band intensity was ranked using a simple four-point scale via two blinded observers and compared with cTnI levels measured by a clinical blood analyzer. Blood was also analyzed for biomarkers of systemic organ damage. HS severity, as previously defined using HR, BP, and recovery Tc profile during heat exposure, correlated strongly with cTnI (R(2) = 0.69) at Tc,Max. POC cTnI band intensity ranking accurately predicted cTnI levels (R(2) = 0.64) and HS severity (R(2) = 0.83). Five markers of systemic organ damage also correlated with ctPOC score (albumin, alanine aminotransferase, blood urea nitrogen, cholesterol, and total bilirubin; R(2) > 0.4). This suggests that cTnI POC tests can accurately determine HS severity and could serve as simple, portable, cost-effective HS field tests.

Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis

BACKGROUND

The global burden of disease attributable to seasonal influenza virus in children is unknown. We aimed to estimate the global incidence of and mortality from lower respiratory infections associated with influenza in children younger than 5 years.

METHODS

We estimated the incidence of influenza episodes, influenza-associated acute lower respiratory infections (ALRI), and influenza-associated severe ALRI in children younger than 5 years, stratified by age, with data from a systematic review of studies published between Jan 1, 1995, and Oct 31, 2010, and 16 unpublished population-based studies. We applied these incidence estimates to global population estimates for 2008 to calculate estimates for that year. We estimated possible bounds for influenza-associated ALRI mortality by combining incidence estimates with case fatality ratios from hospital-based reports and identifying studies with population-based data for influenza seasonality and monthly ALRI mortality.

FINDINGS

We identified 43 suitable studies, with data for around 8 million children. We estimated that, in 2008, 90 million (95% CI 49-162 million) new cases of influenza (data from nine studies), 20 million (13-32 million) cases of influenza-associated ALRI (13% of all cases of paediatric ALRI; data from six studies), and 1 million (1-2 million) cases of influenza-associated severe ALRI (7% of cases of all severe paediatric ALRI; data from 39 studies) occurred worldwide in children younger than 5 years. We estimated there were 28,000-111,500 deaths in children younger than 5 years attributable to influenza-associated ALRI in 2008, with 99% of these deaths occurring in developing countries. Incidence and mortality varied substantially from year to year in any one setting.

INTERPRETATION

Influenza is a common pathogen identified in children with ALRI and results in a substantial burden on health services worldwide. Sufficient data to precisely estimate the role of influenza in childhood mortality from ALRI are not available.

FUNDING

WHO; Bill & Melinda Gates Foundation.

Point of care testing: diagnosis outside the virology laboratory

Numerous point-of-care tests (POCTs) are available to diagnose viral infections in both hospital and community settings. The ideal POCT is rapid, sensitive, specific, and simple to perform. This chapter will describe the benefits of POCTs, factors that can influence the accuracy of POCTs and highlight some limitations of POCT strategies. The sensitivity, specificity, and turn-around time of available POCTs are included for common conditions including respiratory viral infections (e.g. influenza, RSV) and blood-borne viral infections (e.g. HIV).

Comparison of polyurethane foam to nylon flocked swabs for collection of secretions from the anterior nares in performance of a rapid influenza virus antigen test in a pediatric emergency department

Rapid antigen testing of upper respiratory secretions collected with various swab types is often utilized for laboratory diagnoses of influenza virus infection. There are limited data on the effects of swab composition on test performance. This study compared the performance of the Quidel QuickVue Influenza A+B test on secretions from the anterior nares when a polyurethane foam swab was used for collection to that when a nylon flocked swab was used for collection. One hundred subjects who presented to a pediatric emergency department with symptoms suggestive of an influenza virus infection were recruited for the study. Foam and flocked swabs of the anterior nares were obtained from separate nares of each subject before a posterior nasopharyngeal swab was collected and placed into viral transport medium. The QuickVue test was performed directly on each swab type, and the results were compared to the results of reverse transcription-PCR (RT-PCR), direct fluorescent antibody (DFA) test, and viral culture performed on the transport medium. RT-PCR alone and DFA combined with culture were utilized as separate gold standards. There were 56 cases of influenza detected by RT-PCR; the QuickVue test was positive for 40 foam and 30 flocked swabs, for sensitivities of 71% and 54%, respectively (P = 0.01). Similarly, there were 49 influenza cases detected by DFA and/or culture; the QuickVue test was positive for 38 foam and 30 flocked swabs, for sensitivities of 78% and 61%, respectively (P = 0.13). This study suggests that polyurethane foam swabs perform better than nylon flocked swabs for the collection of secretions from anterior nares in the Quidel QuickVue Influenza A+B test.

Early diagnosis of lower respiratory tract infections (point-of-care tests)

PURPOSE OF REVIEW

Respiratory tract infections are a common reason for prescribing antibiotics, although not all of these infections require such therapy. Rapid diagnosis of etiology using point-of-care tests is a potentially useful way of reducing prescriptions of both unnecessary and unnecessarily broad-spectrum antibiotics. This can also lead to the facilitation of appropriate infection control measures to prevent spread of respiratory viruses within institutions.

RECENT FINDINGS

Point-of-care tests are available for diagnosing influenza, respiratory syncytial virus, Streptococcus pneumoniae, and Legionella infections using easily obtainable specimens. Their main benefit is that results can be obtained in about 15 min with reasonable accuracy. In many situations, however, it is still important to confirm diagnosis with more accurate but slower tests such as bacterial cultures with antibacterial susceptibility testing or viral polymerase chain reaction testing.

SUMMARY

Although the sensitivities of many of the rapid diagnostic tests are moderate, when used at the time of initial consultation, they have the potential to reduce costs, length of stay, secondary spread of respiratory viruses, and inappropriate antibiotic prescribing.

Rapid diagnosis of influenza infection in older adults: influence on clinical care in a routine clinical setting

BACKGROUND

Laboratory diagnosis of influenza has previously relied on viral isolation in culture. Rapid antigen tests (RATs) are now available but few studies have examined their use in older adults under routine clinical conditions.

OBJECTIVES

To determine the utility of the RAT in older adults presenting to a large medical center and how test results impacted clinical care.

STUDY DESIGN

Retrospective chart review of patients tested for influenza during the 2003--2004 and 2004--2005 influenza seasons. Clinical data were correlated with the results of laboratory testing.

RESULTS

Eighty-four adults tested positive for influenza. Adding the results of the RAT to symptom complexes predictive of influenza significantly enhanced the ability to diagnose influenza in the acute setting. The positive predictive value of fever plus cough increased from 32% to 92% with a positive RAT. The RAT also directed appropriate antiviral therapy. 20/22 (91%) patients with a positive RAT and symptoms < or =48 h received antiviral treatment compared to only 1/12 (8%) patients with a negative RAT and a positive culture.

CONCLUSIONS

Under routine clinical conditions rapid influenza testing enhances the ability to quickly diagnose influenza and can be used to guide early treatment decisions in older adults.

Point‐of‐care tests for lower respiratory tract infections

Many lower respiratory tract infections (LRTIs) are caused by organisms that do not require antibiotics or could be safely treated with narrow-spectrum antibiotics. Reducing the unnecessary use of antibiotics, particularly broad-spectrum agents, could reduce costs and side effects and delay the emergence of antibiotic-resistant organisms. Various point-of-care tests are becoming available to help clinicians identify the cause of LRTIs at the time of consultation. Point-of-care tests can be used to diagnose influenza, pneumococcal infections, Legionella and respiratory syncytial virus infections, thus allowing early decisions to be made on appropriate management.

Evaluation of a new point-of-care test for influenza A and B virus in travellers with influenza-like symptoms

Point-of-care (POC) tests for influenza facilitate clinical case management, and might also be helpful in the care of travellers who are at special risk for influenza infection. To evaluate influenza POC testing in travellers, a new assay, the ImmunoCard STAT! Flu A and B, was used to investigate travellers presenting with influenza-like symptoms. Influenza virus infection was diagnosed in 27 (13%) of 203 patients by influenza virus-specific PCR and viral culture. The POC test had sensitivity and specificity values of 64% and 99% for influenza A, and 67% and 100% for influenza B, respectively. Combined sensitivity and specificity were 67% and 99%, respectively, yielding positive and negative predictive values of 95%, and positive and negative likelihood ratios of 117 and 0.34, respectively. The convenient application, excellent specificity and high positive likelihood ratio of the POC test allowed rapid identification of influenza cases. However, negative test results might require confirmation by other methods because of limitations in sensitivity. Overall, influenza POC testing appeared to be a useful tool for the management of travellers with influenza-like symptoms.

Methodologic issues regarding the use of three observational study designs to assess influenza vaccine effectiveness

BACKGROUND

Influenza causes substantial morbidity and annual vaccination is the most important prevention strategy. Accurately measuring vaccine effectiveness (VE) is difficult. The clinical syndrome most closely associated with influenza virus infection, influenza-like illness (ILI), is not specific. In addition, laboratory confirmation is infrequently done, and available rapid diagnostic tests are imperfect. The objective of this study was to estimate the joint impact of rapid diagnostic test sensitivity and specificity on VE for three types of study designs: a cohort study, a traditional case-control study, and a case-control study that used as controls individuals with ILI who tested negative for influenza virus infection.

METHODS

We developed a mathematical model with five input parameters: true VE, attack rates (ARs) of influenza-ILI and non-influenza-ILI and the sensitivity and specificity of the diagnostic test.

RESULTS

With imperfect specificity, estimates from all three designs tended to underestimate true VE, but were similar except if fairly extreme inputs were used. Only if test specificity was 95% or more or if influenza attack rates doubled that of background illness did the case-control method slightly overestimate VE. The case-control method usually produced the highest and most accurate estimates, followed by the test-negative design. The bias toward underestimating true VE introduced by low test specificity increased as the AR of influenza- relative to non-influenza-ILI decreases and, to a lesser degree, with lower test sensitivity.

CONCLUSIONS

Demonstration of a high influenza VE using tests with imperfect sensitivity and specificity should provide reassurance that the program has been effective in reducing influenza illnesses, assuming adequate control of confounding factors.

Patients' perceptions of nasopharyngeal aspiration in the emergency department of a teaching hospital in Hong Kong

Nasopharyngeal aspiration (NPA) is the preferred method for collecting specimens for viral culture in patients with respiratory tract infection. As virus identification may influence admission and treatment decisions, it is important to perform NPA in the emergency department. The test may be uncomfortable and poorly tolerated. This prospective study investigated patients' perceptions of NPA. Patients in the emergency department with upper respiratory tract infection undergoing NPA between 9 March 2005 and 12 August 2005 were included. 86 patients (mean (SD) age 47 (23) years; 49 women) were recruited. 22 (26%) patients complained that NPA was very uncomfortable, 59 (69%) reported that it was mildly uncomfortable and 5 (6%) patients reported no discomfort. On a 10-point scale, the median discomfort score was 4. 29 (34%) patients stated that NPA was more uncomfortable than blood taking, 19 (22%) patients felt that both were similar and 38 (44%) patients felt that NPA was less uncomfortable (p value not significant). NPA performed in the emergency department is well tolerated and should be considered in emergency departments when results may influence patient management.

Comparison of two rapid influenza A/B test kits with reference methods showing high specificity and sensitivity for influenza A infection

The rapid detection of influenza viruses is important for forming preventative strategies, directing initiation of anti-viral therapy, detecting potential avian influenza viruses, and excluding influenza-like pathogens, such as SARS. The ImmunoCard STAT! Flu A and B Plus test (Meridian Bioscience, Cincinnati, OH) is a new point of care (POC) test utilizing influenza-specific monoclonal antibodies for rapid diagnosis. The performance of this assay was compared to the established POC Binax NowFlu A and NowFlu B test, and the reference diagnostic standards of viral culture, indirect immunofluorescence (IFA), and RT-PCR where appropriate. Testing of nasopharyngeal aspirates (NPA) from children, throat swabs, and nasal swabs from adults indicated ImmunoCard STAT! specificity of 98% and 100% for influenza A and B, respectively in 224 specimens. The Binax test showed specificity of 99% and 100%, respectively for influenza A and B. Sensitivity results were identical for both rapid detection kits (80% and 47% for Flu A and B, respectively). Overall results were very similar for both testing devices with the advantage of ImmunoCard STAT! Flu A and B Plus test detecting influenza A and B with sharp and easy to read results.