One of the essential steps in treating COVID-19 and stopping the spread of the disease is widespread testing to determine who has been infected. While widespread testing in the U.S. has lagged for a variety of reasons, the good news is that diagnostic procedures have been established, and many labs and companies are working on developing faster testing methods.
Currently, the most common coronavirus testing method is the antigen test, which detects specific proteins from the virus. This method shows positive results in 5 minutes, and negative results in 13 minutes. This method, which uses a platform called ID NOW, allows for samples to be tested on-site, rather than being sent to a lab. Antigen tests are not as sensitive as previous molecular, or RT-PCR, tests and may produce a false negative. Therefore, the antigen tests are approved for use with symptomatic patients only. Despite this drawback, antigen tests are the driving force of point-of-use testing because of their lower cost, simpler design, and ability to produce test results on-site as opposed to being shipped out to a lab.
Both antigen and RT-PCR testing require a healthcare worker to swab a patient’s nose or throat to collect a sample of mucus. The most common method of sample collection has been a nasopharyngeal swab, in which a long Q-tip-like swab is inserted deep into the nasal passage. However, the FDA is now allowing individuals to use short swabs to collect samples from the front of their nostrils. Samples can also be collected from an individual’s throat.
If a patient has a productive cough, healthcare workers can collect a sample of phlegm to be tested, as the Centers for Disease Control and Prevention (CDC) recommends testing lower respiratory tract specimens when available. The CDC also recommends collecting a sample from the lower respiratory tract if the patient is receiving invasive mechanical respiration. It is currently thought that the virus reproduces in the respiratory tract, so samples collected directly from a patient’s lungs may contain more evidence of the virus. The CDC does not recommend inducing phlegm to get a sample.
Patients may still be recommended for a RT-PCR test, particularly when patients show weak symptoms or are asymptomatic, or in situations such as returning to on-site work. When a sample is collected for an RT-PCR test, a healthcare worker swabs the patient’s nose or throat to collect a sample of mucus. This sample is placed in a vial, and shipped to a laboratory for testing. Keeping samples at the right temperature (between 35 and 40 degrees Fahrenheit), and shipping them fast enough (they must be processed within four days, or be frozen or discarded) are critical to ensuring the integrity of the specimen. Otherwise, samples may return inaccurate results.
In the lab, the first step is to extract the RNA, using substances called reagents. Enzymes are then added to complete the reverse-transcriptase process, through which the RNA is turned into DNA. Technicians add more reagents that copy the DNA, as well as fluorescent dyes that indicate the presence of the SARS-CoV-2 virus. The sample goes through a process of heating and cooling, known as polymerase chain reaction, in a special PCR machine. A light-measuring instrument in the PCR machine reads the fluorescent patterns in the sample, which indicates whether the sample does or does not contain the virus.
Generally, the RT-PCR process takes a few hours to complete. However, this time estimate does not include travel time to and from the testing site or any sample backlog the lab might be experiencing. Patients typically receive results within a few days.
Another test that is key in fighting COVID-19 is serology, or antibody tests. These types of tests use blood samples to detect antibodies, which are proteins made in response to infections. If a person has these antibodies in their system, it means they were infected with COVID-19, even if they never became seriously ill or displayed symptoms.
Many individuals who were infected with COVID-19 only displayed mild symptoms, or were completely asymptomatic, and therefore were never tested for the disease. Additionally, because of testing limitations in the early days of the outbreak, some individuals who were symptomatic may have received a false-negative when they got a diagnostic test.
At-home tests allow individuals to collect their own samples, through nasal swabs, and mail or deliver them to labs for testing. They are ideal for individuals who are still under stay-at-home orders, and alleviate some of the burden on healthcare workers, who may lack the gear necessary to protect them from individuals carrying the disease.
Read more: At-home COVID-19 Testing
Knowing exactly who has had COVID-19 will help public health experts understand how widespread the disease is, and may help them develop treatments and vaccines.
As the capacity for diagnostic testing for coronavirus has increased, the guidelines for when to get tested have relaxed somewhat. However, exactly who can get tested and what the steps are varies by location in the U.S.
Currently, the Centers for Disease Control and Prevention (CDC) offers these guidelines for prioritizing who should be tested for the coronavirus:
Individuals who believe they have been exposed to COVID-19, or exhibit symptoms of the disease are still encouraged to contact their individual doctor, or their state or local health department, for guidance on when and how to get tested.
Individuals experiencing any of the following symptoms of severe illness should seek medical attention and testing immediately:
If you are experiencing minor COVID-19 symptoms and are not over 65 or immunocompromised, you should contact your healthcare provider. They will determine if you need to be tested for COVID-19. Your healthcare provider can also provide guidance for treating your symptoms with over-the-counter medications and self-isolating if necessary.
Read more: When to Get Tested for Coronavirus
|Centers for Disease Control and Prevention (CDC)||The CDC is the United States’ leading national public health organization. Its mission is to protect public health and safety through the control and prevention of disease, injury, and disability in the U.S. and abroad.|
|World Health Organization (WHO)||A specialized agency of the United Nations, WHO is responsible for international public health. Headquartered in Geneva, Switzerland, it has field offices worldwide.|
|Association of Public Health Laboratories (APHL)||The APHL is a nonprofit organization in the United States that represents laboratories that protect public health and safety.|
|State Departments of Health||Each state in the U.S. has its own department of health. These public health departments are currently coordinating efforts for COVID-19 testing and treatment.|