- Influenza, or flu, outbreaks are recurrent and every year pose a significant risk to global health
- Influenza affects millions: each year 3m to 5m cases of severe disease and 500,000 deaths
- Pandemics occur about three times a century
- The 1918 flu pandemic killed 21m . . . Total deaths in World War I was 17m
- Effective treatment of patients with respiratory illness depend on accurate and timely diagnosis
- Early diagnosis of influenza can reduce the inappropriate use of antibiotics and provide the option of using antiviral therapy
- Rapid Influenza Diagnostic Tests (RIDTs) are useful in determining whether outbreaks of respiratory disease might be due to influenza
- RIDTs vary in their sensitivity, specificity, complexity, and time to produce results
- There is a pressing need for faster, cheaper, and easier-to-use flu tests with higher levels of sensitivity and specificity than those currently available
- The large, fast-growing, global and under-served RIDT market drives a host of initiatives
- Various development challenges pose significant threats
The critical importance of new rapid influenza diagnostic tests
What challenges face developers of cheap, easy-to-use, rapid and accurate diagnostic tests for influenza, or flu, which improve on tests currently available?
Influenza is a highly contagious respiratory illness caused by a virus, and occurs in distinct outbreaks of varying extent every year. Its epidemiologic pattern reflects the changing nature of the antigenic properties of influenza viruses. The viruses subsequent spread depends upon multiple factors, including transmissibility and the susceptibility of the population. Influenza A viruses, in particular, have a remarkable ability to undergo periodic changes in the antigenic characteristics of their envelope glycoproteins; the hemagglutinin and the neuraminidase. Anyone can get influenza. It is usually spread by the coughs and sneezes of an infected person. You can also catch flu by touching an infected person (e.g. shaking hands). Adults are contagious one to two days before getting symptoms and up to seven days after becoming ill, which means that you can spread the influenza virus before you even know you are infected. Influenza presents as a sudden onset of high fever, myalgia, headache and severe malaise, cough (usually dry), sore throat, and runny nose. There are several treatment options, which aim to ease symptoms until the infection goes, and aims to prevent complications. Most healthy people recover within one to two weeks without requiring any medical treatment. However, influenza can cause severe illness or death especially in people at high risk such as the very young, the elderly, and people suffering from medical conditions such as lung diseases, diabetes, cancer, kidney or heart problems.
Influenza is a cruel, costly killer with a history of pandemics. It causes millions of upper respiratory tract infections every year as it spreads around the world in seasonal epidemics, and poses on-going risks to health. The most vulnerable are the young, the old and those with chronic medical conditions such as heart disease, respiratory problems and diabetes. Each year, on average 5% to 20% of populations in wealthy countries get influenza. In the US it causes more than 200,000 hospitalizations and 36,000 deaths annually, and each year costs the American economy between US$71 to US$167bn.
History of pandemics
The 1918-19 “Spanish Flu” pandemic caused 21m deaths, and was one of three 20th century influenza pandemics. At least four pandemics occurred in the 19th century, and the first pandemic of the 21st century was the 2009 “Swine Flu”. Its virulence and global human impact was less deadly than originally feared, but it still resulted in 18,449 laboratory confirmed deaths. If you account for people who died as a result of complications precipitated by the Swine Flu, the actual death toll is significantly higher. Mindful of the potential accelerated spread of a pandemic subtype of the influenza virus, the World Health Organization (WHO), and national governments continuously monitor influenza viruses. Assessment of pathogenicity and virulence is the key to taking appropriate healthcare actions in the event of an outbreak.
However, without widespread access to improved diagnostic tests, each year millions will not receive timely anti-viral medication, tens of thousands of influenza sufferers will develop complications, and thousands will die unnecessarily, as the growing interconnections and complexity of the world present an increasing challenge to influenza prevention and control.
The influenza viruses
Influenza is a single-stranded, helically shaped, RNA virus of the orthomyxovirus family. Influenza viruses are divided into two groups: A and B. Influenza A has two subtypes which are important for humans: A(H3N2) and A(H1N1). The former is currently associated with most deaths. Influenza viruses are defined by two different protein components, known as antigens, on the surface of the virus. They are haemagglutinin (H) and neuraminidase (N) components. Influenza viruses circulate in all parts of the world, and mutate at a low level, referred to as "genetic drift", which allows influenza to continuously evolve and escape from the pressures of population immunity. This means that each individual is always susceptible to infections with new strains of the virus. "Genetic shift" occurs when a strain of influenza A virus completely replaces one or more of its gene segments with the homologous segments from another influenza A strain, a process known as reassortment. If the new segments are from an animal influenza virus to which humans have had no exposure and no immunity, pandemics may ensue.
Gold standard diagnosis rarely used
The gold standard method for the detection of influenza viruses is rarely performed, as patients with suspected influenza are most likely to be seen by a primary care doctor with limited resources, and the gold standard test requires sophisticated laboratory infrastructure, and takes at least 48 hours. Even the faster Reverse Transcription-Polymerase Chain Reaction (RT-PCR) test, which is a relatively new type of molecular assay that uses isothermal amplification of viral cells, has a turnaround time of four to six hours. It is also expensive, and therefore not commonly used.
The slowness and expense of traditional influenza tests led to the development of an array of commercially available Rapid Influenza Diagnostic Tests (RIDTs), which screen for influenza viruses, and provide results within as little as 15 minutes after sample collection and processing. Such tests are largely immunoassays that can identify the presence of influenza A and B viral nucleoprotein antigens in respiratory specimens and display the results in a qualitative way (positive or negative). About 10 such tests have FDA approval and are available in the US. About 20 have been determined suitable for the European market. All are growing in their usage. However, the RIDTs vary in their sensitivity, specificity, complexity, and in the time needed to produce results.
Tests rule in Influenza but do not rule it out
According to the Centers for Disease Control and Prevention (CDC) the commercially available RIDTs in America have a sensitivity ranging from 50% to 70%. This means that in up to 50% of influenza cases, test results will still be negative. A study showed that tests for the N1H1 virus, a subtype of influenza A that was the most common cause of the Swine Flu in 2009, and is associated with the 1918 Spanish Flu pandemic, have a sensitivity ranging from 32% to 50% depending on the brand of test. A 2012 meta-analysis of the accuracy of RIDTs reported an average sensitivity for detecting influenza in adults of only 54%. Sensitivity in children is somewhat higher since they tend to shed a greater quantity of virus. Thus some 30% to 50% of flu samples that would register positive by the gold standard viral culture test may give a false negative when using a RIDT, and some may indicate a false positive when a person is not infected with influenza. Thus, RIDTs that are currently available allow Influenza to be ruled in but not ruled out. More sensitive tests are needed.
New flu tests
There are a number of innovative nano-scale molecular diagnostic influenza tests in development, which are expected to deliver more accurate validations than existing antigen-based molecular tests. The new tests use a platform, comprised of an extremely thin layer of material, which detects the presence of influenza proteins in saliva or blood. This is attached to an electronic chip, which transforms the platform into a sensor. This is an essential part of the measuring device as it converts the input signal to the quantity suitable for measurement and interpretation. The presence of influenza proteins in saliva or blood triggers an electrical signal in the chip, which is then communicated to a mobile phone.
Here Roger Kornberg, Professor of Medicine at Stanford University and 2006 Nobel Laureate for Chemistry describes how advances in molecular science are enabling the replacement of traditional in vitro diagnostics with rapid, virtually instantaneous point-of-care diagnostics without resort to complex processes or elaborate infrastructure. Antiviral drugs for influenza are available in some countries and may reduce severe complications and deaths. Ideally they need to be administered early (within 48 hours of onset of symptoms) in the disease. An almost instantaneous point-of-care test will enable better access to appropriate treatment particularly in primary care:
Notwithstanding all the recent scientific advances, new and innovative influenza detection tests will need to overcome significant challenges to outperform current RIDTs. In addition to the usual challenges associated with sensitivity and specificity, new developers have to be aware of recent changes in immunochromatographic antigen detection testing for influenza viruses, and the rapid development of commercially available nucleic acid amplification tests. Also, there are the usual development challenges associated with miniaturization, fabrication, scaling, marketing, and regulation. Effective from 13 February 2017, the FDA reclassified antigen based rapid influenza detection tests from class I into class II devices. Class II devices are higher risk than Class I, and require greater regulatory controls to provide reasonable assurance of the device’s safety and effectiveness. This was provoked by the potential for the devices to fail to detect newer versions of the influenza virus. For instance, a novel variant of influenza A,H7N9, has emerged in Asia, and H5N1 is also re-emergent.
Another challenge, especially for start-ups with limited resources, is the fluctuating nature of the influenza virus itself. A bad year for patients, when influenza causes millions of people to become ill, is a good year for manufacturers of RIDTs. Conversely, a good year for patients, when influenza affects a lower percentage of the population, is a bad year for manufacturers who suffer from unsold inventory, and reduced revenues. Thus, the vagaries of the flu virus not only have the potential to kill millions of people, they also pose a significant threat to start-ups dedicated to developing RIDTs.
Despite all the challenges, there is a significant commercial opportunity in the current under-served global RIDT market for improved tests. Each year, in the US, more than 1bn people visit primary care doctors, and in the UK, the NHS, deals with over 1m patients every 36 hours. The global in vitro diagnostics market was valued at US$60bn in 2016. Between 2016 and 2021, the market is expected to grow at a CAGR of 5.5% to reach US$79bn by 2021. Over the same period, the global point-of-care diagnostics sub-market is expected to grow at a CAGR of 10% to reach US$37bn by 2021. Large corporates, small start-ups, and university research laboratories have spotted the opportunity, and started developing new and innovative RIDTs. Given that each-year influenza causes widespread morbidity as well as mortality, it should be a matter of priority to support all efforts to develop swift and reliable RIDTs. A significant step forward would be a RIDT with greater sensitivity and usability such that the test could be administered and a result given within a 10-minute primary care consultation.