What is the difference between the various COVID-19 tests?
The NAAT (also called PCR) is a nucleic acid amplification test that identifies active disease. A deep nasal swab collects viral laden secretions, and identifies the viral DNA. It is currently the most reliable test, but may take a day or two to get results (while the DNA is being “amplified”). A positive test is (almost) always truly positive. A negative test is usually truly negative, though it will miss a few, so if a person is very sick or very early in the course of their disease it may need to be repeated.
The Antigen test is also a nasal swab that identifies active disease. It is popular because results can be obtained in minutes to hours, but it is more likely to miss a positive case than the NAAT. If the antigen test is positive, it is likely correct, but should be confirmed with a NAAT. If it’s negative, you can’t be certain you don’t have COVID-19, so if you are ill you should stay away from others and consider having a NAAT.
An antibody test is a blood test that is designed to measure the body’s immune response to a COViD-19 infection. It won’t become positive until 2-4 weeks after having had the infection, and may disappear over the next several months. The tests are not very useful in most instances at this time. If positive, you likely had COVID-19 whether or not you had symptoms, but it doesn’t tell you whether or not you are still contagious, nor whether the antibodies will protect you from being reinfected. The major benefit of the antibody test at this time is that if positive, you might be eligible to donate plasma which might be life-saving for someone with severe disease.
What is a “close contact”?
A “close contact” is someone with a significant exposure to the SARS CoV-2 virus. This is defined as being within 6 feet of a COVID-19 case for 15 minutes or more, or contact with their secretions (eg. sharing a bathroom, picking up their used tissues), or being in a enclosed area (small room, airplane). This doesn’t mean you can’t catch COVID from 7 feet away or in less than 15 minutes. It just means you are less likely to, and allows for epidemiologic and contact tracing of those most at risk.
What is a “presumptive case”?
For epidemiologic purposes, a presumptive case is someone who hasn’t yet had an NAAT (PCR) test, but has a positive Antigen test and either 2 COVID-19 symptoms or a significant COVID-19 exposure.
What is a “confirmed case”?
A “confirmed case” is a person who has a positive NAAT (PCR nasal swab).
What is COVID-19?
COVID-19 is the disease caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). The virus attaches to cells in the lungs, blood vessels, kidney, and heart and can cause pneumonia, blood clots, kidney damage, heart damage, brain infection.
How is SARS-CoV-2 transmitted?
The infection primarily spreads directly from person-to-person, usually via respiratory droplets from close range. Infection can also occur if a person touches an infected surface and then touches his or her eyes, nose, or mouth. Droplets typically do not travel more than six feet (about two meters). Aerosolized virus (from shouting, coughing, sneezing, singing) may travel farther.
When are people most infectious?
Infected individuals are more likely to be infectious about 2 days prior to having any symptoms and are much less infectious by their seventh day of symptoms. It is also possible to be infected, have no symptoms at all, and still infect others.
If I am exposed to SARS-CoV-2, how long until I become ill?
The incubation period for COVID-19 is thought to be within 14 days following exposure. Most cases develop within four to five days after exposure.
Can I catch COVID-19 and not know it?
Yes, infection without symptoms is well documented and probably common. A person with no symptoms but a positive test may still have lung abnormalities on a CAT scan.
Where am I most likely to catch COVID-19?
Most secondary infections have been noted among household contacts, congregate living situations (such as nursing homes), health care settings, and in closed settings (such as cruise ships). However, there have been many clusters of cases after social, religious or work gatherings.
How accurate is testing?
Tests for COVID-19 are new, and determining their accuracy is challenging.
A positive PCR test (usually a nasal swab) generally confirms the diagnosis of COVID-19, but a negative test may be wrong 30% of the time. More accurate tests are being developed.
Antibody tests identify an immune response to the virus, but it is not yet known whether these antibodies protect against reinfection, nor how long such protection would last.
What symptoms do people get with COVID-19?
Pneumonia is the most frequent serious manifestation of infection, with fever, cough, and shortness of breath. Other common symptoms include muscle aches, diarrhea, and smell or taste disorders. Not all patients have fever. In a small number of patients, loss of smell or taste may be their only symptom. Sometimes the first symptoms of infection are nausea and diarrhea. Other reported symptoms include headache, sore throat, runny nose and conjunctivitis.
There are no specific symptoms that can distinguish COVID-19 from other viral respiratory infections. The only way to distinguish influenza and other respiratory viral illnesses from COVID-19 is by testing.
How sick do people get with COVID-19?
In one of the largest studies from China (44,500 confirmed infections) :
- Mild disease was reported in 81 percent.
- Severe disease was reported in 14 percent.
- Critical disease was reported in 5 percent.
- The death rate was 2.3 percent; no deaths were reported among noncritical cases
Who is at risk for severe illness?
Severe illness can occur in otherwise healthy individuals of any age, but it predominantly occurs in adults with advanced age or underlying medical conditions.
How does age affect risk?
Individuals of any age can become infected, although adults of middle age and older are most commonly affected, and older adults are more likely to have severe disease. In one large study, 67 % of cases were diagnosed in those aged ≥45 years, and 80 %of deaths occurred in those aged ≥65 years. Symptomatic infection in children appears to be relatively uncommon; when it does occur, it is usually mild, although severe cases and deaths have been reported.
What conditions have been associated with more severe illness and death?
- Heart disease
- High blood pressure
- Chronic lung disease
- Cancer (in particular blood cancers, lung cancer, and metastatic cancers)
- Chronic kidney disease
- Immunocompromising conditions
- Liver disease
African American, Latino and Native American individuals also appear have a disproportionately high number of infections and deaths due to COVID-19, possibly related to underlying socioeconomic disparities.
How long does the illness last?
The illness is often prolonged, lasting approximately two weeks in those with mild disease and three to six weeks in those with severe disease.