Influenza, better known as the common flu, is a viral respiratory disease that can have debilitating effects. The symptoms of the flu can be mild or severe and, in some cases, even fatal. Influenza testing is used to identify samples of the virus present in respiratory secretions.
Influenza is a seasonal virus that strikes between fall and spring every year. According to the Centers for Disease Control and Prevention (CDC), millions of Americans are affected by the influenza virus each year. Some tell-tale signs of influenza are symptomatic such as:
- Muscle spasms
- Chills
- Exhaustion
- Headache
- Stuffy nose
- Fever
- Sore throat
- Cough
These symptoms tend to last longer than they do when seen in the common cold.
We have come to understand that there are two types of influenza virus, type-A, and type-B, which are to blame for most annual flu pandemics and epidemics. Type-C influenza causes mild respiratory discomfort and has not been implicated in any epidemic. Then there are numerous sub-types of the Type-A virus, characterized by specific antigenic components, hemagglutinin (H) and neuraminidase (N). H1N1 and H3N2 are the most common culprits in human infections.
It is common for doctors to diagnose and treat an influenza patient without actually testing for the virus. This is even more common when a specific strain has already been documented in the vicinity. But influenza testing can help to rule out the presence of other conditions. This can help preserve limited supplies of antibiotics in misdiagnosis and allow for antiviral therapy to be applied early in the contamination when it will be most effective.
Furthermore, if there is an outbreak confirmed in a controlled or confined environment, such as a hospital, nursing home, or school, proper diagnostic testing can help pinpoint the cause of the outbreak. Influenza testing is also beneficial to state and local health officials and the CDC looking to track the spread of the virus through human communities.
Because the behavior of the influenza outbreak will be different each year, testing will provide the CDC with a better understanding of the virus types in circulation each year. They can then collect these viruses' samples, develop improved vaccinations, and monitor strains that show a higher resistance to antiviral treatment.
Influenza testing is also an excellent way to diagnose an influenza condition and apply proper treatments accurately. Sometimes influenza testing is performed to test for the presence of the virus within a closed community, such as a school, nursing home hospital, etc. Testing will be done to discover the type and strain of the virus so that proper treatments and preventive measures can be taken.
But not all strains of influenza require testing or the prescription of special antiviral treatments. Often treatment and diagnosis can be provided without laboratory testing. Such a diagnosis will be based on symptoms of influenza, flu season, and the presence of other cases in the area.
If the cases are outside of the 3–5-day window in which antiviral treatment is most effective, the symptoms of the illness are not severe, and there is no risk of secondary complications, the patient may be sent home to rest, stay hydrated, and soothe the symptoms of the virus with OTC medication.
Of course, it is also important to remember that the flu can be deadly. Testing for the presence of the virus can help health practitioners minimize the spread of the virus and mitigate the severity of the symptoms when it does strike.
The Center for Disease Control recommends testing in the following situations:
· Patients in a hospital with a high risk of contracting or suspicion of infection with the flu virus.
· Cases in which a flu test will better understand the current contagion level and allow health officials to control the spread of the virus through society or the community.
Testing can also be done to look for new strains of the virus and prevent future pandemics, monitor for strains of the virus with resistance to antiviral medication, and prepare for the next year's flu season.
There are many different types of influenza testing available. The kind you will need will depend on availability and the reason for the test.
- Rapid flu tests: depending on the type of test applied, testing can be done at the doctor's office or the bedside of the patient in as little as 20 minutes. Samples can also be sent to a laboratory for more in-depth testing, and the results will typically be ready the very same day. But rapid tests will have varying capacities to identify specific types of flu strains. For example, one night only identifies type-A but not B or detects both but does not distinguish between the two. Some of the more advanced options can indeed determine the presence of A and B types, and some can take this a step forward and identify the sub-strains of Type A like H1N1.
- Rapid influenza diagnostic test antigen detection: this method of testing will detect the presence of viral infection in nasal secretions. Rapid antigen tests generally detect between 50% - 70% of influenza types. For this reason, the CDC applies this method of testing liberally if there is even the slightest suspicion of infection, even if the results are negative. Confirmation for negative results can be found in a virus culture testing or a more sensitive molecular analysis. Sometimes these tests will result in a positive even if the patient doesn't have the flu.
- Real-Time Reverse Transcription Polymerase Chain Reaction (RT-PCR): along with other types of molecular testing, Real-time Reverse Transcription Polymerase Chain Reaction testing seeks clues of the virus presence in respiratory samples. This type of testing is especially sensitive and designed to detect the influenza virus, much more so than antigen testing is. Depending on the type of method applied, this method of testing can identify as many as 66% to 100% of influenza cases. Some specific types of molecular testing performed in the most advanced laboratories can test simultaneously for several different types of respiratory virus, including rhinovirus, respiratory syncytial virus, and the flu virus.
· Viral culture: in this type of testing, the virus is collected and grown until it can be better identified. A fully developed sample will provide laboratory analysts a better picture of the A or B type of influenza or the presence of some other respiratory condition. But viral cultures are an expensive form of testing; this makes them less practical in simply determining if a person has the flu virus and making individual decisions for them. These tests are better suited to understanding the nature of the virus itself or confirming a positive result from one of the other tests. Viral cultures can also be sent to the public health laboratories to provide them with a better picture of the virus strains active in their local community. This is how the public became alerted to the presence of the H5N1 Avian flu back in 2009.
Additional laboratory testing can also be used to rule out other types of infection that may have similar symptoms and provide a clearer understanding of what exactly is causing an illness.
· RSV test: applied to detect syncytial virus, a virus most common in young children and the elderly
· Strep test: often used to check a group for A streptococcus, the bacteria that cause strep throat
When is testing ordered?
Flu tests are most often required in flu season toward the end of fall and early spring. This is especially true when that person is hospitalized or suffering from a weakened immune system or any other health considerations that place them at special risk. Testing is typically done within 3 days of the first onset of symptoms that indicate the illness could be influenza.
Some of these symptoms include:
- Headaches
- Fever, chills
- Muscle aches
- Weakness and fatigue
- Stuffy nose
- Sore throat
- Cough
- With some flu strains, diarrhea, and vomiting
When influenza has not been documented in an area, a doctor may ask for testing to properly document the outbreak. This is also important to provide an effective diagnosis for the first patient to contract influenza within the region.
Testing is often ordered during outbreaks of respiratory conditions, especially when influenza is a suspected contributor to the condition.
Testing may also be performed on someone who has died while exhibiting symptoms characteristic of influenza.
What does the test result mean?
A positive result to a flu test generally means that the person does indeed have influenza type-A or type-B and should begin some sort of antiviral treatment to improve the symptoms. But a simple test may not tell the individual or the health practitioners examining the case which type of strain is being examined. It will also not tell of the severity of the symptoms or what secondary implications may be involved.
Some rapid tests can correctly identify the presence of the influenza virus including, H1N1, influenza type-A, as well as other types of viruses like RSV.
A viral culture is one of the best ways to learn more about the viral profile in lab samples. If the viral presence is influenza, the doctors will have a live sample of the virus they can use to identify and use in their strategies in the war on the viral plague.
Is there anything else I should know?
Whether they receive treatment or not, viral infections will typically disappear within a couple of weeks. But fatigue and a lingering cough may be felt for long after this. In some cases, serious secondary conditions may occur as well. These complications typically strike just as the symptoms of influenza are wearing off.
Everyone is at risk of contracting the flu, but suitable treatment must be provided right away for the following groups of people:
- The very young
- The elderly
- Those with a weaker immune system
- Those with a history of respiratory conditions
Complications can arise from the flu, including sepsis, encephalitis, and even pneumonia. These conditions can be very serious and require professional medical treatment to address.
Can I test negative and still have the flu?
Yes. Influenza tests will not detect every single instance of infection without fail. Rapid antigen testing is rated at 50%-70% effective, and molecular testing has been rated 66%-100% effective, depending on the various tests used and how they are applied. A negative result from a test may also mean there were not sufficient amounts of viral evidence to be detected. Furthermore, there are new strains of influenza being discovered, and some samples may escape detection.
What other tests might my doctor order to properly diagnose my flu-like symptoms?
Your health care provider may order a test for strep throat, another condition with symptoms very similar to those found in influenza. An RSV test can reveal the presence of a respiratory syncytial virus, which is especially prevalent among small children and the elderly. They may also suggest a sputum culture that can identify other specific bacterial or fungal presence in your respiratory tract. Your healthcare practitioner may also order other blood tests that are typically used to monitor the health of the organs, like the lungs and kidneys. This could include a complete blood count (CBC) or a comprehensive metabolic panel (CMP).
Why is the flu such a big deal?
Fighting the flu and building a better understanding of this considerable health threat is especially important to the general population and personal health. In 1918, the deadly Spanish flu killed a portion of the world's population, as many as 50 million people internationally. From 1957 to 1968, hundreds of thousands died from Asian and Hong Kong flu variants.
There has been a reason for great concern over various types of flu in recent years. The H5N1 and H7N9 subtypes of Type-A influenza have been under more scrutiny than before. Some of these subtypes of influenza cause recurring outbreaks in human populations. There is reason to believe they may cause even more problems in the future.
Should I get a flu shot?
The CDC recommends that everyone older than 6-month should get the flu shot at the beginning of each flu season. This is especially important for those with a higher risk of contracting the disease or a lower immune function than normal; this includes children, the elderly, pregnant women, nursing home staff, and those who have pre-existing conditions like COPD or Asthma.
- Children
- The elderly
- Pregnant women
- Nursing home staff
- Those who have pre-existing conditions like COPD or Asthma
Can I still get the flu if I've had the vaccine?
It is possible to contract the flu even after you have been vaccinated since it is generally regarded that no vaccine is 100% effective. But it is generally understood that after you have been vaccinated, the effects of the virus will be decreased. Furthermore, it also takes a certain amount of time for the body to learn from a vaccine about and build immunity (antibodies) against a flu strain.
Which strains are in the vaccine each year?
Each year a vaccine is made from a combination of the strains most likely to strike that flu season. These strains are selected by health care experts that track viral patterns in circulation each year and understand which strains will be seen each season.
As the influenza virus passes through populations of the world, it mutates or changes. This is called the "antigenic drift" and allows the virus to shift from previous forms that have been present in this area. This makes it harder to treat with the vaccines currently on hand. The amount of antigenic drift experienced each year will vary. But the more significant the antigenic drift, the greater the number of illnesses as fewer people will be immune.
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