Comparison of two new rapid antigen detection assays for respiratory syncytial virus with another assay and shell vial culture

Diagnostic Accuracy of Rapid Antigen Detection Tests for Respiratory Syncytial Virus Infection: Systematic Review and Meta-analysis

Respiratory syncytial virus (RSV) rapid antigen detection tests (RADT) are extensively used in clinical laboratories. We performed a systematic review and meta-analysis to evaluate the accuracy of RADTs for diagnosis of RSV infection and to determine factors associated with accuracy estimates. We searched EMBASE and PubMed for diagnostic-accuracy studies of commercialized RSV RADTs. Studies reporting sensitivity and specificity data compared to a reference standard (reverse transcriptase PCR [RT-PCR], immunofluorescence, or viral culture) were considered. Two reviewers independently extracted data on study characteristics, diagnostic-accuracy estimates, and study quality. Accuracy estimates were pooled using bivariate random-effects regression models. Heterogeneity was investigated with prespecified subgroup analyses. Seventy-one articles met inclusion criteria. Overall, RSV RADT pooled sensitivity and specificity were 80% (95% confidence interval [CI], 76% to 83%) and 97% (95% CI, 96% to 98%), respectively. Positive- and negative-likelihood ratios were 25.5 (95% CI, 18.3 to 35.5) and 0.21 (95% CI, 0.18 to 0.24), respectively. Sensitivity was higher in children (81% [95% CI, 78%, 84%]) than in adults (29% [95% CI, 11% to 48%]). Because of this disparity, further subgroup analyses were restricted to pediatric data (63 studies). Test sensitivity was poorest using RT-PCR as a reference standard and highest using immunofluorescence (74% versus 88%; P < 0.001). Industry-sponsored studies reported significantly higher sensitivity (87% versus 78%; P = 0.01). Our results suggest that the poor sensitivity of RSV RADTs in adults may preclude their use in this population. Furthermore, industry-sponsored studies and those that did not use RT-PCR as a reference standard likely overestimated test sensitivity.

Community acquired respiratory and gastrointestinal viral infections: challenges in the immunocompromised host

PURPOSE OF REVIEW

Newer molecular diagnostic techniques have advanced the field of clinical microbiology and infectious diseases, particularly with respect to characterizing the role that community acquired viruses play in the clinical course and outcomes of the immunocompromised host. This review will examine recent studies describing the impact of adenovirus, rhinovirus, hepatitis E and norovirus in the course of solid organ and stem cell transplant recipients, as well as their epidemiology and implications for infection prevention and control.

RECENT FINDINGS

Adenovirus transmission is poorly understood; recent studies increasingly point to reactivation of latent infection in the immunocompromised host. Rhinovirus shedding can persist for weeks after acute viral infection, complicating hospital infection control policies. Hepatitis E is increasingly recognized as a potential pathogen in the stem cell and solid organ transplant population, and should be considered in the work-up for unexplained liver function test abnormalities. Similar to rhinovirus, norovirus shedding from the gastrointestinal tract may persist for months in the immunocompromised host; infected patients are at a higher risk for transmitting norovirus compared with infected healthcare workers.

SUMMARY

Additional studies are needed, particularly with respect to transmission, for these community acquired viral infections, which often have devastating consequences in the immunocompromised patient population.

Laboratory methods for determining pneumonia etiology in children

Laboratory diagnostics are a core component of any pneumonia etiology study. Recent advances in diagnostic technology have introduced newer methods that have greatly improved the ability to identify respiratory pathogens. However, determining the microbial etiology of pneumonia remains a challenge, especially in children. This is largely because of the inconsistent use of assays between studies, difficulties in specimen collection, and problems in interpreting the presence of pathogens as being causally related to the pneumonia event. The laboratory testing strategy for the Pneumonia Etiology Research for Child Health (PERCH) study aims to incorporate a broad range of diagnostic testing that will be standardized across the 7 participating sites. We describe the current status of laboratory diagnostics for pneumonia and the PERCH approach for specimen testing. Pneumonia diagnostics are evolving, and it is also a priority of PERCH to collect and archive specimens for future testing by promising diagnostic methods that are currently under development.

Molecular diagnosis of respiratory virus infections

The appearance of eight new respiratory viruses, including the SARS coronavirus in 2003 and swine-origin influenza A/H1N1 in 2009, in the human population in the past nine years has tested the ability of virology laboratories to develop diagnostic tests to identify these viruses. Nucleic acid based amplification tests (NATs) for respiratory viruses were first introduced two decades ago and today are utilized for the detection of both conventional and emerging viruses. These tests are more sensitive than other diagnostic approaches, including virus isolation in cell culture, shell vial culture (SVC), antigen detection by direct fluorescent antibody (DFA) staining, and rapid enzyme immunoassay (EIA), and now form the backbone of clinical virology laboratory testing around the world. NATs not only provide fast, accurate and sensitive detection of respiratory viruses in clinical specimens but also have increased our understanding of the epidemiology of both new emerging viruses such as the pandemic H1N1 influenza virus of 2009, and conventional viruses such as the common cold viruses, including rhinovirus and coronavirus. Multiplex polymerase chain reaction (PCR) assays introduced in the last five years detect up to 19 different viruses in a single test. Several multiplex PCR tests are now commercially available and tests are working their way into clinical laboratories. The final chapter in the evolution of respiratory virus diagnostics has been the addition of allelic discrimination and detection of single nucleotide polymorphisms associated with antiviral resistance. These assays are now being multiplexed with primary detection and subtyping assays, especially in the case of influenza virus. These resistance assays, together with viral load assays, will enable clinical laboratories to provide physicians with new and important information for optimal treatment of respiratory virus infections.

Emerging advances in rapid diagnostics of respiratory infections

Recent developments in rapid diagnostics for respiratory infections have mostly occurred in the areas of antigen and nucleic acid detection. Nucleic acid amplification tests have improved the ability to identify respiratory viruses in clinical specimens and have played pivotal roles in the rapid characterization of new viral pathogens. Antigen-detection assays in immunochromatographic or similar formats are most easily developed as near-patient tests, although they have been developed commercially only for a limited range of respiratory pathogens. New approaches for respiratory pathogen detection are needed, and breath analysis is an exciting area with enormous potential.

Antigen-based assays for the identification of influenza virus and respiratory syncytial virus: why and how to use them in pediatric practice

This article describes the clinical and socioeconomic relevance of influenza (IV) and respiratory syncytial virus (RSV) in pediatrics, the characteristics and limitations of currently available assays, and the impact of rapid diagnostic tests. This article shows that rapid tests for the detection and identification of IV and RSV in the respiratory secretions of infants and children are useful in the diagnosis of common, and possibly severe diseases, such as influenza and bronchiolitis. The tests' specificity and sensitivity make them most reliable when the prevalence of influenza or RSV infection is high, which suggests that their routine use should be restricted to the peak periods of viral circulation. The most recently marketed tests are similarly effective in identifying viruses, and so pediatricians should choose those that are less expensive, less time consuming, and easier to perform and to interpret.

Developments in immunologic assays for respiratory viruses

In most hospitals, clinics, and doctor's offices, immunologic assays are the only tests performed on site for the diagnosis of respiratory viruses. More than other methods, immunoassays have been shown to affect patient management and save costs, aiding early administration of antiviral therapy, reduction in unnecessary tests and antibiotics, and earlier discharges. This article discusses the major immunologic methods employed for respiratory virus diagnosis, recent developments in immunoassays and sample collection, and current test algorithms.

Respiratory syncytial virus prophylaxis in a tertiary care neonatal intensive care unit

Nosocomial transmission of respiratory syncytial virus (RSV) is a serious, preventable cause of RSV infection. Passive RSV prophylaxis became available in 1996. We compared the RSV nosocomial infection rate in our neonatal intensive care unit before and after RSV prophylaxis, using nosocomial rotavirus infections as a comparator. There were no significant differences between nosocomial RSV infection rates before and after institution of prophylaxis.

Comparison of viral isolation and multiplex real-time reverse transcription-PCR for confirmation of respiratory syncytial virus and influenza virus detection by antigen immunoassays

We evaluated the Prodesse ProFlu-1 real-time reverse transcription-PCR multiplex assay with the SmartCycler instrument for the detection of human respiratory syncytial virus (RSV) and influenza A and B viruses in comparison to conventional cell culture and antigen immunoassays with the BD Directigen A+B and Binax NOW RSV assays over two successive respiratory virus seasons. Ninety-two percent of the 361 specimens tested were nasopharyngeal aspirates obtained from individual patients, of which 119 were positive for RSV and 59 were positive for influenza virus. The median age of the patients whose specimens were positive for RSV and influenza virus were 6.3 months and 42.4 years, respectively. The specificity of all of the methods tested was >or=99%, and the individual sensitivities of NOW RSV, RSV culture, Directigen A+B, influenza virus culture, and the Proflu-1 PCR for influenza/RSV were 82% (95% confidence interval [CI], 73 to 88), 57% (95% CI, 44 to 69), 59% (95% CI, 44 to 72), 54% (95% CI, 38 to 69), and 98% (95% CI, 93 to 100)/95% (95% CI, 85 to 99), respectively. In a clinical setting where viral isolation is performed to confirm rapid antigen immunoassay results for these common respiratory viruses, one-step real-time reverse transcriptase PCR testing can be a more sensitive and timely confirmatory method.

Detection of respiratory viruses by molecular methods

SUMMARY

Clinical laboratories historically diagnose seven or eight respiratory virus infections using a combination of techniques including enzyme immunoassay, direct fluorescent antibody staining, cell culture, and nucleic acid amplification tests. With the discovery of six new respiratory viruses since 2000, laboratories are faced with the challenge of detecting up to 19 different viruses that cause acute respiratory disease of both the upper and lower respiratory tracts. The application of nucleic acid amplification technology, particularly multiplex PCR coupled with fluidic or fixed microarrays, provides an important new approach for the detection of multiple respiratory viruses in a single test. These multiplex amplification tests provide a sensitive and comprehensive approach for the diagnosis of respiratory tract infections in individual hospitalized patients and the identification of the etiological agent in outbreaks of respiratory tract infection in the community. This review describes the molecular methods used to detect respiratory viruses and discusses the contribution that molecular testing, especially multiplex PCR, has made to our ability to detect respiratory viruses and to increase our understanding of the roles of various viral agents in acute respiratory disease.

Performance of indirect immunofluorescence assay, immunochromatography assay and reverse transcription-polymerase chain reaction for detecting human respiratory syncytial virus in nasopharyngeal aspirate samples

Comparison of the use of indirect immunofluorescence assay (IFA), immunochromatography assay (ICA-BD) and reverse transcription-polymerase chain reaction (RT-PCR) for detecting human respiratory syncytial virus (HRSV) in 306 nasopharyngeal aspirates samples (NPA) was performed in order to assess their analytical performance. By comparing the results obtained using ICA-BD with those using IFA, we found relative indices of 85.0% for sensitivity and 91.2% for specificity, and the positive (PPV) and negative (NPV) predictive values were 85.0% and 91.2%, respectively. The relative indices for sensitivity and specificity as well as the PPV and NPV for RT-PCR were 98.0%, 89.0%, 84.0% and 99.0%, respectively, when compared to the results of IFA. In addition, comparison of the results of ICA-BD and those of RT-PCR yielded relative indices of 79.5% for sensitivity and 95.4% for specificity, as well as PPV and NPV of 92.9% and 86.0%, respectively. Although RT-PCR has shown the best performance, the substantial agreement between the ICA-BD and IFA results suggests that ICA-BD, also in addition to being a rapid and facile assay, could be suitable as an alternative diagnostic screening for HRSV infection in children.

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.

Comparison of BD Directigen EZ RSV and Binax NOW RSV tests for rapid detection of respiratory syncytial virus from nasopharyngeal aspirates in a pediatric population

The BD Directigen EZ RSV (BD) assay and the Binax NOW RSV (BN) assays are lateral flow immunochromatographic assays used in the rapid diagnosis of respiratory syncytial virus (RSV) infection. A prospective study was undertaken to compare the performance characteristics of the BD and BN assays using 99 fresh nasopharyngeal aspirate specimens from children. All specimens were cultured by tube cultures and R-mix shell vials. Culture-negative specimens that tested positive by 1 or both antigen tests were analyzed by reverse transcriptase polymerase chain reaction (RT-PCR) for the presence of RSV nucleic acids. Specimens positive by culture and/or RT-PCR were considered true positives. The sensitivity, specificity, positive predictive value, and negative predictive value for BD were 90%, 94%, 94%, and 90%, respectively, and those for BN were 90%, 100%, 100%, and 90% respectively. The overall agreement between the 2 assays was 93% (confidence interval, 86.3-96.6%). Three specimens negative by both assays were positive by viral culture. The rapid lateral flow immunochromatographic assays were easy to perform and easy to interpret, and the results are available in less than 30 min. The reduced turnaround time offered by these assays is particularly useful in the rapid detection of RSV infections in children from outpatient settings.

Prospective evaluation of rapid antigen tests for diagnosis of respiratory syncytial virus and human metapneumovirus infections

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) are two important viral pathogens that cause respiratory tract infections in the pediatric population. The rapid detection of these agents allows the prompt isolation and treatment of infected patients. In the present prospective study, we evaluated the performances of four rapid antigen detection assays, including a rapid chromatographic immunoassay (CIA) for RSV (Directigen EZ RSV; Becton Dickinson, Sparks, MD), a direct fluorescent-antibody assay (DFA) for RSV (Bartels; Trinity Biotech, Carlsbad, CA), and two DFAs for hMPV manufactured by Diagnostic Hybrids Inc. (DHI; Athens, OH) and Imagen (Oxoid Ltd., Basingstoke, Hampshire, United Kingdom). The clinical specimens tested comprised 515 nasopharyngeal aspirates submitted to the Clinical Microbiology Laboratory at Hartford Hospital from 1 November 2006 to 21 April 2007. Compared to the results of real-time reverse transcription-PCR (RT-PCR), the CIA had a sensitivity of 79.8% and a specificity of 89.5%. The RSV DFA with Bartels reagents showed a sensitivity of 94.1% and a specificity of 96.8%. For hMPV, the sensitivity and specificity were 62.5% and 99.8%, respectively, for the DHI DFA and 63.2% and 100%, respectively, for the Imagen DFA. The hands-on and test turnaround times for CIA were 10 and 30 to 60 min, respectively, and the hands-on and test turnaround times for the RSV and hMPV DFAs were 30 and 105 min, respectively. We conclude that while the RSV CIA is user-friendly, it lacks sensitivity and specificity, especially during off-peak months. In contrast, the RSV DFA is more sensitive and specific, but interpretation of its results is subjective and it demands technical time and expertise. Similarly, both hMPV DFAs are highly specific in comparison to the results of RT-PCR, but their sensitivities await further improvements.

[Respiratory viruses: old and new. Review of diagnostic methods]

Acute respiratory infections (ARI) of viral origin are one of the main causes of morbidity and mortality worldwide. In addition to traditional viruses, such as the influenza virus, respiratory syncytial virus, rhinovirus, parainfluenza viruses 1 to 4, and adenovirus, other viruses such as metapneumovirus, new coronaviruses (human coronavirus NL63 and HKU1 and severe acute respiratory syndrome [SARS]-coronavirus), and recently bocaviruses, have been identified as causal agents of ARI. Although most of these viral infections follow a benign and selflimiting course in healthy adults, the consequences for the health care systems increase when they involve children, the elderly, immunosuppressed individuals, or those with chronic underlying diseases. These viral infections are an important cause of hospitalization and death, mainly during the cold months of the year, and, from a social-health perspective, ARI are a drain on economic resources and a frequent cause of work absenteeism. Occasionally, some of these viruses may cause emergent world health problems, as has occurred with the influenza virus pandemic strain and SARScoronavirus. While classical diagnostic methods based on culture and antigen detection remain useful for traditional respiratory viruses, recently described viruses are diagnosed mainly by molecular amplification techniques.

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.

Performance of a rapid assay (Binax NOW) for detection of respiratory syncytial virus at a children's hospital over a 3-year period

A rapid assay, Binax NOW RSV, was compared to viral culture for 14,756 pediatric respiratory specimens obtained from 2003 to 2006. There were 794 viral culture-confirmed respiratory syncytial virus infections. Sensitivity was 81%, and specificity was 93.2%. Sensitivity was greatest for neonates (91.1% versus 80.7% [P < 0.01]).

Respiratory syncytial virus detection by Remel Xpect, Binax Now RSV, direct immunofluorescent staining, and tissue culture

The performance characteristics of Xpect RSV (XP) and Binax Now RSV (BN) were compared to those of direct fluorescent-antibody staining and/or tissue culture for detection of respiratory syncytial virus (RSV) in nasopharyngeal aspirate and wash samples from children (n = 110) and adults (n = 66). The sensitivity, specificity, positive predictive value, and negative predictive value of XP were 75%, 98%, 95%, and 90%, respectively; and those of BN were 74%, 100%, 100%, and 90%, respectively. The performances of the assays were similar within a given age group and specimen type (nasopharyngeal aspirate or wash specimen). XP and BN are useful for screening for RSV in respiratory specimens when large volumes are tested or low levels of staffing occur.

Cost of influenza hospitalization at a tertiary care children's hospital and its impact on the cost-benefit analysis of the recommendation for universal influenza immunization in children age 6 to 23 months

OBJECTIVE

To calculate the costs of influenza hospitalization at a tertiary care children's hospital as the basis of a cost-benefit analysis of the new influenza vaccine recommendation for children age 6 to 23 months.

STUDY DESIGN

We reviewed the medical records of all patients admitted to Children's Memorial Hospital (CMH) in 2002 diagnosed with influenza. Total hospital costs were obtained from the Business Development Office.

RESULTS

Thirty-five charts were analyzed. Both of the 2 patients requiring mechanical ventilation and 4 of 6 patients admitted to the intensive care unit had high-risk underlying medical conditions. Nine children were age 6 to 23 months; 4 of these 9 had no preexisting medical conditions. Had all 18 high-risk children over age 6 months been protected from influenza, approximately $350,000 in hospital charges could have been saved.

CONCLUSIONS

Preventing the additional 4 hospitalizations in the otherwise low-risk children age 6 to 23 months for whom vaccine is currently recommended would have cost approximately $281,000 ($46/child) more than the hospital charges saved. When all children age 6 to 23 months are considered, influenza vaccination is less costly than other prophylactic measures. Addition of indirect costs, deaths, outpatient costs, and the cost of secondary cases would favor the cost:benefit ratio for influenza vaccination of all children age 6 to 23 months.