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Compilation of CDC guidelines for novel coronavirus antigen testing

 Last Update: 2022-05-16
 Source: Internet
 Author: User

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Hong Kong and Shanghai have already used antigen detection as a screening test for large-scale populations.

Website address: Centersfor Disease Control and Prevention https:// CDC website includes: testing strategies, antigen testing guidelines, antibody testing guidelines, antibody testing, nucleic acid testing, point-of-care and rapid testing, and combined testing on laboratory testing for COVID-19

Detection strategy

key point

This guidance describes and compares detection strategies for different types of SARS-CoV-2, including intended use and application, regulatory requirements, and reporting requirements

This guidance is for those providing and performing SARS-CoV-2 testing

diagnostic test

Diagnostic tests are designed to identify a patient's current infection and should be performed on anyone with signs and symptoms consistent with COVID-19 and/or with recent known or suspected exposure to SARS-CoV-2

Examples of diagnostic tests include:

Test anyone with symptoms of COVID-19

Testing vaccinated and unvaccinated people who have been in contact with confirmed or suspected cases of COVID-19

screening test

Screening tests are identifying people who have not been vaccinated against COVID-19 and are asymptomatic and do not know, suspect or report exposure to SARS-CoV-2

Examples of screening tests include:

employees at workplace

School students, teachers and staff

people before or after the trip

No one in the home with symptoms related to COVID-19 and who has not been in contact with someone with COVID-19

Public Health Surveillance Test

Public health surveillance is the continuous, systematic collection, analysis, and interpretation of health-related data essential to the planning, implementation, and evaluation of public health practice

Public health surveillance is monitoring disease outbreaks at the community or population level, or describing the incidence and prevalence of disease

Public health surveillance can sample a proportion of a specific population to monitor increases or decreases in prevalence, or to determine the impact of community interventions, such as social distancing, on populations

Regulatory Requirements for Diagnosis, Screening, and Public Health Surveillance

Any laboratory or testing site that performs diagnostic or screening tests must have a Clinical Laboratory Improvement Amendments (CLIA) certificate and meet all applicable CLIA requirements

Reporting of diagnostic, screening and public health surveillance test results

Both diagnostic and screening test results should be reported to the person receiving the test sample and/or their health care facility, and public health surveillance test results should not be reported directly to the person being tested or to their health care facility

Table 1 Summary of SARS-CoV-2 detection strategies

SARS-CoV-2 antigen testing guidance for health care providers testing individuals in the community

key point

This guidance applies to healthcare facilities ordering antigen testing, issuing antigen testing results, or performing point-of-care testing, as well as laboratory and testing professionals and public health practitioners performing antigen testing and reporting in a laboratory setting or in the field

The purpose of this technical guide is to support the effective clinical and public health use of antigen testing for different testing situations

This guideline focuses on the use of antigen testing to diagnose new infections

Guidance for individuals conducting antigen self-tests can be found on the CDC's Self-Test webpage

General Guidance

Antigen testing is commonly used to diagnose other respiratory pathogens, including influenza virus and respiratory syncytial virus (RSV)

Antigen tests are immunoassays that detect the presence of specific viral antigens, and a positive test indicates a current infection
.
Antigen testing on nasopharyngeal, nasal swab or saliva samples is currently authorized
.
Currently authorized antigen tests include point-of-care testing, laboratory testing and self-testing
.
Certain tests are age-restricted
.

Antigen tests produce results quickly (within about 15-30 minutes), and most are available at the point of care
.
Antigen detection for SARS-CoV-2 is generally less sensitive than real-time reverse transcription polymerase chain reaction (RT-PCR) and other nucleic acid amplification assays (NAAT), which detect and amplify the presence of viral nucleic acids
.
However, NAATs may remain positive for weeks to months after initial infection, and viral nucleic acid levels are detectable even when virus cannot be cultured, suggesting that the presence of viral nucleic acid is not always indicative of infectivity
.

Antigen testing and NAAT (if required) need to be properly interpreted for accurate clinical management of persons with suspected COVID-19, as well as to identify infected persons when used for screening
.

The clinical presentation of diagnostic tests depends largely on the conditions in which they are used
.
Antigen testing and NAAT work best if patients are tested while they are symptomatic
.
Although antigen tests are generally less sensitive than NAAT, they can also be used to detect infection, with special attention to the conditions in which they are used, as described below
.

Antigen tests have been used for COVID-19 screening tests in congregate settings such as nursing homes, dormitories, homeless shelters, and correctional facilities
.
Screening tests have rapidly identified people with COVID-19, informing infection prevention and control measures to prevent transmission
.
In situations like these, where rapid test turnaround time is critical, providing immediate results through antigen testing is valuable
.

Healthcare facilities and public health practitioners should understand the test performance characteristics used to interpret results, identify potential false-negative or false-positive test results, and guide confirmatory testing and management of test subjects
.
Laboratories and testing professionals who perform antigen testing should be aware of the factors that affect the accuracy of antigen testing, as described in this guide
.
Healthcare providers, laboratory and testing professionals, and public health practitioners should also be aware of the differences between diagnostic, screening, and surveillance tests
.

Regulatory requirements for the use of SARS-CoV-2 antigen testing

FDA regulates in vitro diagnostic devices, COVID-19 tests and test systems used for diagnostic or screening tests, including test systems for antigen testing, must receive an EUA from the FDA or be in accordance with the FDA's COVID-19 Testing Policy.
FDA Each SARS-CoV-2 antigen test authorized for use is included on the FDA's list of in vitro diagnostic EUAs
.
The intended use of each test provided in the Instructions for Use and Authorization Letter defines the population for which the test is intended to be used, acceptable sample types, and how the results should be used
.

Laboratories and testing professionals using antigen tests for diagnostic or screening tests for SARS-CoV-2 must also comply with the Clinical Laboratory Improvement Amendments (CLIA) regulations
.
Any laboratory or testing site that intends to report patient-specific test results to an individual or healthcare facility must first obtain a CLIA certificate and meet all requirements to perform the test
.

Performance of SARS-CoV-2 antigen detection

For healthcare facilities and testing professionals, understand the performance characteristics of the antigen tests in use, including sensitivity, specificity, and positive and negative predictive values, and follow the manufacturer's instructions for use that summarize the performance characteristics, which One point is important
.

The "gold standard" for clinical diagnostic testing for SARS-CoV-2 remains laboratory-based (moderate and high complexity) NAAT
.
Therefore, institutions may choose to use laboratory-based NAAT to confirm antigen test results, especially if the antigen test results are inconsistent with the clinical situation
.

Table 2 summarizes some of the differences between NAAT and antigen testing
.
The clinical presentation of NAAT and antigen tests may differ from clinical utility when considering issues such as test availability, quality of specimen collection and shipping, and turnaround time for results
.
Depending on their directions for use, some point-of-care NAATs may not be available for confirmatory testing
.
NAATs that produce putative results are not suitable for confirmatory testing
.

Table 2 Summary of some differences between nucleic acid amplification testing (NAAT) and antigen testing

Note: *The decreased sensitivity of the antigen test may be offset if the point-of-care antigen test is repeated more frequently (i.
e.
serial tests are performed at least weekly)
.

+ Refers to point-of-care antigen testing only
.

Antigen levels in samples taken before symptoms appear or later in the infection process may be below the detection limit of detection, resulting in a false-negative antigen test result, while more sensitive tests, such as most NAATs, can give a positive result
.
Research has shown that the antigen test has comparable sensitivity to the laboratory's NAAT when the viral load in the sample is high and the patient is likely to be most infectious
.

The specificity of the antigen test is comparable to NAAT, which means that false positive test results are less likely to occur when the antigen test is used according to the manufacturer's instructions
.
Despite the high specificity of antigen tests, false-positive results can still occur, especially when used when the probability of pre-testing or infection is low—a situation that applies to all in vitro diagnostic tests
.
In general, for all diagnostic tests, the lower the community infection rate, the higher the rate of false positive test results
.

The positive and negative predictive values of all in vitro diagnostic tests (eg, NAAT and antigen tests) depend on the pretest probability
.
The predicted probability takes into account both the prevalence of the target infection in the tested population and the clinical background of the tested individual
.
If the community infection rate is high, the tested person is symptomatic, and the probability of an alternative diagnosis is low, the probability of pre-testing is generally considered to be high
.
If the community infection rate is low, and the tested person is asymptomatic and has no close contacts of COVID-19 patients, the probability of pre-screening is generally considered to be low
.

2.
Use of SARS-CoV-2 antigen detection in community settings

2.
2.
Use of SARS-CoV-2 antigen detection in community settings SARS-CoV-2 antigen detection in community settings

Figure 1 Antigen testing protocol in a community setting

Technical Description

1.
If testing is required after contact with a suspected patient, test 5 days after the last close contact with a COVID-19 patient
.

2.
If the patient has a high probability of being infected with SARS-CoV-2 (eg, in an area with a high community level of COVID-19 or the patient has had close or suspected contact with someone infected with SARS-CoV-2), or The patient has symptoms of COVID-19
.

3.
A positive antigen test result generally does not require a confirmatory test; however, when the likelihood of the patient being infected is low (eg, at a low community level of COVID-19 and no known close contact with someone infected with SARS-CoV-2) region), consider doing so
.

4.
Confirmatory NAAT testing should be performed as soon as possible after antigen testing, and no more than 48 hours after the initial antigen testing
.
If the results are inconsistent, confirmatory test results should be used as the decisive basis for clinical diagnosis
.
If performing serial antigen tests, wait 24-48 hours between tests
.

Testing symptomatic people in community settings

In a community setting, when testing a person with symptoms consistent with COVID-19, healthcare providers can often interpret a positive antigen test as a patient infected with SARS-CoV-2; this person should follow CDC guidance for isolation
.

A positive antigen test result in a symptomatic person usually does not require a confirmatory test; however, it may be considered if the patient has a low likelihood of being infected with SARS-CoV-2, and factors that indicate a low likelihood of infection include living with COVID- 19 Areas with a low community level and no known close contact with someone infected with SARS-CoV-2
.

A negative antigen test result in symptomatic patients should usually be confirmed by a laboratory NAAT
.
In this setting, serial antigen testing every 2-3 days while symptomatic can be used as an alternative to confirmatory NAAT testing
.
Antigen testing of symptomatic individuals may not be required if symptomatic individuals are less likely to be infected with SARS-CoV-2
.

Symptomatic individuals who are then NAAT-confirmed positive should follow the CDC's isolation guidance from the date of the first test with a negative antigen test result
.
Alternative diagnoses should be considered for symptomatic individuals with a negative antigen test result followed by a negative NAAT confirmation and avoid close contact with others to prevent disease transmission
.

Testing asymptomatic people in community settings

When testing an asymptomatic person for COVID-19 in a community setting, healthcare providers can often interpret a positive antigen test as a patient infected with SARS-CoV-2; this person should follow CDC guidance for isolation
.
If a patient has a low probability of being infected with SARS-CoV-2, a confirmatory test for a positive antigen test result in an asymptomatic person may be required
.
For example, a person with a lower likelihood of contracting SARS-CoV-2 is someone who has not been in close contact with someone with COVID-19 and lives in a community with a low COVID-19 community level
.

When testing asymptomatic individuals for COVID-19, healthcare providers can often interpret a negative antigen test result as not detecting the SARS-CoV-2 virus
.
However, if an asymptomatic person has a high probability of being infected with SARS-CoV-2, a confirmatory test with a laboratory-based NAAT for a negative antigen test result may be required
.
For example, people who are more likely to be infected with SARS-CoV-2 are people who have had close or suspected contact with someone with COVID-19
.

Asymptomatic individuals with a negative antigen test result who have been in close or suspected contact with a COVID-19 patient and who have not been vaccinated in time should follow the CDC's isolation guidance
.

Confirmatory testing when using SARS-CoV-2 antigen testing

As indicated by the antigen testing protocol, confirmatory testing may be required regardless of the person being tested's symptoms or exposure status
.
Confirmatory testing should be performed as soon as possible after antigen testing and no more than 48 hours after initial antigen testing
.
If the interval between two sample collections is more than 48 hours, or if there is a new opportunity for exposure, the laboratory's NAAT should be considered a separate test, not a confirmation of a previous test
.
If the results of antigen testing and confirmatory NAAT are inconsistent, in general, confirmatory test results should be interpreted as definitive for clinical diagnosis
.

The CDC recommends using a laboratory's NAAT for confirmatory testing
.
CDC does not recommend the use of oral samples (such as saliva) for NAAT for confirmatory testing, but instead recommends the use of samples most suitable for testing, such as nasopharyngeal, middle turbinate, and anterior nasal swabs
.

Several studies have documented continuous or intermittent detection of the virus using RT-PCR after recovery; in these cases, these individuals do not appear to infect others
.
Therefore, if the person being tested has recently been infected with COVID-19 and has completed isolation, the patient may receive a negative antigen test result and a positive confirming NAAT, suggesting continued detection of SARS- CoV-2
.
For this reason, repeat testing after initial diagnostic testing or as a cure test is not recommended during isolation
.

Serial testing when using antigen testing

Depending on the situation and circumstances, it may be helpful to conduct serial antigen tests for people who have a negative antigen test result
.
There is evidence that serial antigen testing every few days can identify SARS-CoV-2 in the early stages of infection, thereby reducing disease transmission
.
Serial antigen testing in group living settings, such as long-term care facilities or correctional or detention facilities, can rapidly identify patients infected with SARS-CoV-2 and help prevent further spread
.
Confirmatory testing using NAAT may not be required when serial antigen testing is performed on a person with a negative antigen test result
.

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