In the absence of a “gold standard,” researchers are finding a high frequency of false negatives among SARS-CoV-2 RT-PCR tests
Serology tests designed to detect antibodies to the SARS-CoV-2 coronavirus that causes the COVID-19 illness have been dogged by well-publicized questions about accuracy. However, researchers also are raising concerns about the accuracy of molecular diagnostics which claim to detect the actual presence of the coronavirus itself.
“Diagnostic tests, typically involving a nasopharyngeal swab, can be inaccurate in two ways,” said Steven Woloshin, MD, MS, in a news release announcing a new report that “examines challenges and implications of false-negative COVID-19 tests.” Woloshin is an internist, a professor at Dartmouth Institute, and co-director of the Geisel School of Medicine at Dartmouth.
“A false-positive result mistakenly labels a person infected, with consequences including unnecessary quarantine and contact tracing,” he stated in the news release. “False-negative results are far more consequential, because infected persons who might be asymptomatic may not be isolated and can infect others.”
Woloshin led a team of Dartmouth researchers who analyzed two studies from Wuhan, China, and a literature review by researchers in Europe and South America that indicated diagnostic tests for COVID-19 are frequently generating false negatives. The team published their results in the June 5 New England Journal of Medicine (NEJM).
For example, one research team in Wuhan collected samples from 213 hospitalized COVID-19 patients and found that an approved RT-PCR test produced false negatives in 11% of sputum samples, 27% of nasal samples, and 40% of throat samples. Their research was published on the medRxiv preprint server and has not been peer-reviewed.
The literature review Woloshin’s team studied was also published on medRxiv, titled, “False-Negative Results of Initial Rt-PCR Assays for COVID-19: A Systematic Review.” It indicated that the rate of false negatives could be as high as 29%. The authors of the review looked at five studies that had enrolled a total of 957 patients. “The collected evidence has several limitations, including risk of bias issues, high heterogeneity, and concerns about its applicability,” they wrote. “Nonetheless, our findings reinforce the need for repeated testing in patients with suspicion of SARS-Cov-2 infection.”
Another literature review, published in the Annals of Internal Medicine, titled, “Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction–Based SARS-CoV-2 Tests by Time Since Exposure,” estimated the probability of false negatives in RT-PCR tests at varying intervals from the time of exposure and symptom onset. For example, the authors found that the median false-negative rate was 38% if a test was performed on the day of symptom onset, versus 20% three days after onset. Their analysis was based on seven studies, five of which were peer-reviewed, with a total of 1330 test samples.
Doctors also are seeing anecdotal evidence of false negatives. For example, clinicians at UC San Diego Health medical center treated a patient with obvious symptoms of COVID-19, but two tests performed on throat samples were negative. However, a third test, using a sample from a bronchial wash, identified the virus, reported Medscape.
Sensitivity and Specificity of COVID-19 Clinical Laboratory Tests
The key measures of test accuracy are sensitivity, which refers to the ability to detect the presence of the virus, and specificity, the ability to determine that the targeted pathogen is not present. “So, a sensitive test is less likely to provide a false-negative result and a specific test is less likely to provide a false-positive result,” wrote Kirsten Meek, PhD, medical writer and editor, in an article for ARUP Laboratories.
“Analytic” sensitivity and specificity “represent the accuracy of a test under ideal conditions in which specimens have been collected from patients with either high viral loads or a complete absence of exposure,” she wrote. However, “sensitivity and specificity under real-world conditions, in which patients are more variable and specimen collection may not be ideal, can often be lower than reported numbers.”
In a statement defending its ID Now molecular point-of-care test, which came under scrutiny during a study of COVID-19 molecular tests by NYU Langone Health, Northwell Health, and Cleveland Clinic, according to MedTech Dive, Abbott Laboratories blamed improper sample collection and handling for highly-publicized false negatives produced by its rapid test. An FDA issued alert about the test on May 14 noted that Abbott had agreed to conduct post-market studies to identify the cause of the false negatives and suggest remedial actions.
Issues with Emergency Use Authorizations
In their NEJM analysis, Woloshin et al point to issues with the FDA’s process for issuing Emergency Use Authorizations (EUAs). For example, they noted variations in how manufacturers are conducting clinical evaluations to determine test performance. “The FDA prefers the use of ‘natural clinical specimens’ but has permitted the use of ‘contrived specimens’ produced by adding viral RNA or inactivated virus to leftover clinical material,” they wrote.
When evaluating clinical performance, manufacturers ordinarily conduct an index test of patients and compare the results with reference-standard test, according to the Dartmouth researchers. For people showing symptoms, the reference standard should be a clinical diagnosis performed by an independent adjudication panel. However, they wrote, “it is unclear whether the sensitivity of any FDA-authorized commercial test has been assessed in this way.” Additionally, a reference standard for determining sensitivity in asymptomatic people “is an unsolved problem that needs urgent attention to increase confidence in test results for contact-tracing or screening purposes.”
“To truly determine false negatives, you need a gold standard test, which is essentially as close to perfect as we can get,” Stephen Rawlings, MD, PhD, (above), a resident physician of internal medicine and infectious diseases fellow at UC San Diego’s Center for AIDS Research (CFAR), who has been working on SARS-CoV-2 test validation since March. “But there just isn’t one yet for coronavirus,” he told Medscape. (Photo copyright: University of California, San Diego.)
Continued adherence to current measures, such as physical distancing and surface disinfection.
Development of highly sensitive and specific tests or combinations of tests to minimize the risk of false-negative results and ongoing transmission based on a false sense of security.
Improved RT-PCR tests and serological assays.
Development and communication of clear risk-stratified protocols for management of negative COVID-19 test results.
“These protocols must evolve as diagnostic test, transmission, and outcome statistics become more available,” they wrote.
Meanwhile, clinical laboratories remain somewhat on their own at selecting which COVID-19 molecular and serology tests they want to purchase and run in their labs. Complicating such decisions is the fact that many of the nation’s most reputable in vitro diagnostics manufacturers cannot produce enough of their COVID-19 tests to meet demand.
Consequently, when looking to purchase tests for SARS-CoV-2, smaller medical laboratory organizations find themselves evaluating COVID-19 kits developed by little-known or even brand-new companies.
‘Aerosol and Surface Stability’ study shows that the virus can remain infectious in aerosol form for hours and on surfaces for days
By now, clinical laboratory workers, microbiologists, and phlebotomists should be fully aware of the potential for transmission on surfaces of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the novel coronavirus that causes Coronavirus disease 2019 (COVID-19). The CDC’s latest Morbidity and Mortality Weekly Report revealed that the coronavirus “was identified on a variety of surfaces in cabins of both symptomatic and asymptomatic infected passengers up to 17 days after cabins were vacated on the Diamond Princess, but before disinfection procedures had been conducted,” the New York Post reported. That means the virus can survive on surfaces significantly longer than CDC previously believed.
But did you know a recent study published in the New England Journal of Medicine (NEJM) found that SARS-CoV-2 can also survive in the air for many hours, potentially allowing aerosolized transmission of the virus as well?
The NEJM study also showed that the stability of SARS-CoV-2 to survive on surfaces and in aerosolized form mirrors the stability of the SARS coronavirus (SARS-CoV) that caused the severe acute respiratory syndrome (SARS) outbreak of 2003.
This is critically important information for clinical laboratory professionals in open-space laboratories, phlebotomists collecting medical laboratory specimens, and frontline healthcare workers who come in direct contact with potentially infected patients. They should be aware of every potential COVID-19 transmission pathway.
Hospital infection control teams will be particularly
interested in the possibility of airborne transmission, as they often visit
infected patients and are tasked with tracking both the source of the infection
as well as individuals who may be exposed to sick patients.
The NEJM study, titled “Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1” was conducted by scientists at the National Institute of Allergy and Infectious Diseases (NIAID), an agency of the US Department of Health and Human Services (HHS), the Centers for Disease Control and Prevention (CDC), Princeton University, and University of California, Los Angeles. The researchers concluded that SARS-CoV-2 remains in the air “up to three hours post aerosolization.”
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They also found the virus was detectable for up to four
hours on copper and up to 24 hours on cardboard. The scientists concluded SARS-CoV-2
can remain on plastic and stainless-steel surfaces for two to three days,
though the amount of the virus on surfaces decreases over time.
“Our results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days,” the study states. “These findings echo those with SARS-CoV-1, in which these forms of transmission were associated with nosocomial spread and super-spreading events, and they provide information for pandemic mitigation efforts.”
But Can COVID-19 Be Caught Through Air?
However, as noted in Wired, the researchers did not clearly state that infected persons can spread COVID-19 to others in the same airspace. Some experts have pointed out that there is a difference between a virus that can exist as an aerosol—defined as a liquid or solid suspended in gas under only limited conditions—and the measles virus, for example, which the CDC estimates “can live for up two hours in an airspace where the infected person has coughed or sneezed.”
“While the researchers tested how long the virus can survive
in aerosols suspended in the air, they didn’t actually sample the air around
infected people,” Wired noted. “Instead, they put the virus into a
nebulizer and puffed it into a rotating drum to keep it airborne. Then, they
tested how long the virus could survive in the air inside the drum.”
Neeltje van Doremalen, PhD, a research fellow at National Institutes of Health (NIH) and researcher at the NIAID’s Rocky Mountain Laboratories in Hamilton, Montana, who coauthored the NEJM study, cautioned against an overreaction to this latest research. On Twitter she wrote, “Important: we experimentally generated [COVID-19] aerosols and kept them afloat in a drum. This is not evidence of aerosol transmission.”
Nonetheless, the World House Organization (WHO) took note of the study’s findings and on March 16, 2020, announced it was considering “airborne precautions” for healthcare workers, CNBC reported in its coverage of a virtual press conference on March 16, 2020, led by Maria Van Kerkhove, MS, PhD, Technical Lead for WHO’s Middle East Respiratory Syndrome Coronavirus (MERS-CoV) Task Force.
Van Kerkhove emphasized that health officials were
monitoring results from other studies investigating how environmental
conditions such as humidity, temperature, and ultraviolet light affect
the disease and its ability to live on different surfaces.
“When you do an aerosol-generating procedure like in a medical care facility, you have the possibility to what we call aerosolize these particles, which means they can stay in the air a little bit longer,” said Maria Van Kerkhove, MS, PhD (above), Technical Lead for WHO’s Middle East Respiratory Syndrome Coronavirus (MERS-CoV) Task Force during a virtual press conference, CNBC reported. “It’s very important that healthcare workers take additional precautions when they’re working on patients and doing these procedures,” she added. [Photo copyright: World Health Organization/YouTube.)
To Be or Not to Be an Airborne Pathogen
Stanley Perlman, MD, PhD, Professor of Microbiology and Immunology at the University of Iowa, believes aerosol transmission ultimately will be found not to play a large role in COVID-19 transmission.
“I think the answer will be, aerosolization occurs rarely, but not never,” Perlman told STAT. “You have to distinguish between what’s possible and what’s actually happening.”
In an NEJM editorial, Perlman expanded on those thoughts. “Although specific anti-coronaviral therapies are still in development, we now know much more about how to control such infections in the community and hospitals, which should alleviate some of this fear,” he wrote. “Transmission of [SARS-CoV-2] probably occurs by means of large droplets and contact and less so by means of aerosols and fomites, on the basis of our experience with SARS-CoV and MERS-CoV. Public health measures, including quarantining in the community as well as timely diagnosis and strict adherence to universal precautions in healthcare settings, were critical in controlling SARS and MERS. Institution of similar measures will be important and, it is hoped, successful in reducing the transmission of [SARS-CoV-2].”
An NIH news release announcing the SARS-CoV-2 stability study highlighted two additional observations:
“If the viability of the two coronaviruses is
similar, why is SARS-CoV-2 resulting in more cases? Emerging evidence suggest
that people infected with SARS-CoV-2 might be spreading virus without
recognizing, or prior to recognizing, symptoms. That would make disease control
measures that were effective against SARS-CoV-1 less effective against its
successor.
In contrast to SARS-CoV-1, most secondary cases
of virus transmission of SARS-CoV-2 appear to be occurring in community
settings rather than healthcare settings. However, healthcare settings are also
vulnerable to the introduction and spread of SARS-CoV-2, and the stability of
SARS-CoV-2 in aerosols and on surfaces likely contributes to transmission of
the virus in healthcare settings.”
Clearly, the scientific community has not agreed on
aerosolization as a definite source of infection. Nevertheless, clinical
laboratory workers in settings where potential exposure to SARS-CoV-2 exists
should take precautions against airborne transmission until scientists can
definitively determine whether this latest coronavirus can be acquired through
the airborne transmission.
Professor-led classroom lectures end as students are expected to do much of their traditional learning outside of class. Will this influence how many medical students go on to choose pathology for their residency?
Medical Colleges, hospital universities, and healthcare trade schools nationwide are considering “Active Learning” techniques to replace lectures. These bastions of higher education—where anatomic pathologists, medical laboratory scientists, doctors, nurses, clinical laboratory technicians, and other healthcare professionals learn their skills—are adopting evidence-based teaching styles that resonate with modern technology-savvy students.
“What we know about learning in general is different than it was decades ago,” Lisa Howley, PhD, AAMC Senior Director of Strategic Initiatives and Partnerships, told Inside Higher Education. “Our medical students are of a generation that has grown up differently when it comes to technology and the impact that has on their ability to receive and retain information.”
Dubbed a “flipped classroom,” students do homework before classes rather than after, as would be done in a traditional education setting. They are expected to learn material online and through textbooks, and then complete self-assessments to gauge their understanding of what they’ve learned. Classroom time involves so-called “active learning,” which includes problem-solving in small groups, question-and-answer sessions, and group discussions.
A growing body of research, such as this study published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), indicates that active learning improves student performances, especially in science, technology, engineering, and mathematics. With the specialties of pathology and medical laboratory medicine heavily dependent on technology and science, this may be a favorable development for medical students who decided to specialize in these fields.
“We teach evidence-based medicine all the time,” William Jeffries, PhD, Senior Associate Dean for Medical Education at UVM, stated in the Inside Higher Education article. “If you have the evidence to show one treatment is better than the other, you would naturally use that treatment. So, if we know that there are methods superior to lecturing, why are we lecturing at all?”
Kelly J. (McDonough) Butnor, MD (center), Surgical Pathologist and Professor of Pathology and Laboratory Medicine at University of Vermont College of Medicine, conducts a team-based learning session with second-year students. (Photo and caption copyright: The Washington Post, Erin Post, Larner College of Medicine.)
In “Lecture Halls without Lectures—A Proposal for Medical Education,” published in the New England Journal of Medicine (NEJM), Prober and Heath wrote, “Students are being taught roughly the same way they were taught when the Wright brothers were tinkering at Kitty Hawk.” They suggested five years ago that active learning and short online videos were more effective and a better use of students’ limited time than auditorium-style mandatory lectures. Today, with mobile technologies and streaming Internet technologies, their argument is even more valid.
Lack of Funds Blocks Innovation
Jeffries contends the cost of making wholesale changes in how students are taught, which requires retraining faculty and renovating classrooms, keeps most medical schools from overhauling teaching methods. “Most schools do not have the resources to turn the battleship around,” he told Inside Higher Education.
At UVM, however, a $66-million gift last year by Robert Larner, MD, and his wife Helen, is helping fund the school retrain its medical school teaching staff and redesign classroom spaces to support active learning. Larner is a dual-degree alum whose name now adorns the medical school.
In a recent NEJM article, Richard M. Schwartzstein, MD, Professor, Beth Israel Deaconess Medical Center (BIDMC) at Harvard Medical School, and David H. Roberts, MD, Dean for External Education at Harvard Medical School, point out that “the movement away from traditional lecture-based courses has been under way in US medical schools for more than three decades.” They question, however, whether the push to do away with all lectures is “merely the latest fad in medical education” or is it truly evidence-based?
“We can often serve our students best by fusing elements of various methods, such as team-based or case-based learning and interactive large-group learning sessions, rather than feeling obliged to adhere to a particular format,” they wrote. “But we must also use evidenced-based approaches whenever possible and rigorously evaluate our innovations, acknowledging that important outcomes may include student engagement and problem-solving skills, team dynamics, and the learning environment as much as exam scores.”
Prober told the Washington Post that medical school students already vote with their feet for the type of teaching format they prefer.
“When you go into a lecture in medical schools across the nation, you will find a minority of students actually present,” he said. “Medical students are adults. One generally believes adults try to make decisions that are in their best interests. They have seemingly made the decision that it is not in the lectures.”
For the past two decades, many pathologists have regularly pointed out that advances in technologies and procedures in both anatomic pathology and clinical laboratory medicine have outpaced the ability of medical schools and residency programs to incorporate these new developments into training programs. Thus, clinical laboratory scientists and pathologists will be watching with interest to see if these new models for medical school education are capable of incorporating new advances in laboratory medicine into their training formats in a timely fashion.
Authors of the published study wrote that use of HD optical technology during colonoscopies gives patients a faster answer and may eliminate the need to refer biopsies to pathologists
High definition optical technology is reaching the point where gastroenterologists are able to identify pre-cancerous polyps with 96% accuracy during colonoscopies, according to a recent study conducted at the Mayo Clinic. Pathologists will want to pay close attention to the published findings of this study. That’s because GI biopsies represent a significant proportion of specimens referred to anatomic pathologists.
Similar study of exome sequencing at UCLA produces findings that mirror the diagnostic outcomes produced by researchers at the three Houston organizations
In this expanded study, published in the November 12, 2014, issue of the Journal of the American Medical Association (JAMA), 504 patients (25.2%) received a molecular diagnosis and 92 patients (4.6%) benefitted from medical intervention to ameliorate or eliminate negative symptoms. (more…)
