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Living Evidence - rapid testing

Living evidence tables provide high level summaries of key studies and evidence on a particular topic, and links to sources. They are reviewed regularly and updated as new evidence and information is published.

Quantitative reverse transcription-PCR (RT-qPCR) assay for COVID-19 using upper and lower respiratory tract specimens (nasopharyngeal swab, throat swab and sputum) is considered the gold standard for diagnosing COVID-19.

Rapid point-of-care tests provide results within minutes of the test being administered, allowing for rapid decisions about patient care. It also provides the possibility to extend testing to geographically isolated communities and populations that cannot readily access onsite diagnostic services.

Table one - Test types

  NAAT (RT-PCR) Rapid antigen tests Rapid molecular testsRapid antibody tests

Definition

Detect SARS-CoV-2 viral (Ribonucleic acid) RNA

Identify virus proteins, often using disposable single-use devices

Detect the virus’s genetic material, using small portable or table-top devices

Currently in Australia, TGA have approved six test devices.

Detect human antibodies produced in the days and weeks after a person is infected

Sensitivity

99.91 - 99.98%

False negative rates that subsequently turn positive cases, in symptomatic patients early in the disease, have been estimated to be as high as 20% to 30%

72% (symptomatic)

58% (asymptomatic)

Results are better early in disease. It is not clear whether all tests pick up the delta variant.

73%* (ID NOW)

100%* (Xpert Xpress)

*Insufficient data to investigate the effect of symptom status or time after symptom onset

The combination of IgG/IgM:

30% (for 1 to 7 days)

72% (for 8 to 14 days)

91% (for 15 to 21 days)

Specificity

97.4 - 99.1%

At times where infections are rare, population prevalence surveys have shown false positive rate of RT‐PCR of less than 0.077%

99.6% (overall summary specificity in symptomatic and asymptomatic patients)

99.7%* (ID NOW)

97.2%* (Xpert Xpress)

*Insufficient data to investigate the effect of symptom status or time after symptom onset

98%

Specimen type

Nasal, Nasopharyngeal, Oropharyngeal, Sputum, Saliva

Mostly Nasal, Nasopharyngeal

Some studies have used oropharyngeal and saliva

Mostly Nasal, Nasopharyngeal

Some studies have used oropharyngeal and saliva, not all instruments TGA registered or validated for saliva.

Blood test (serology)

Time to perform the test

Generally less than 24 hours after the laboratory receives specimen.

Most range from 15 minutes–30 minutes

Approximately 15 minutes (ID NOW)

Approximately 60 minutes (Xpert Xpress)

Time varies depending on assay and device type

Up to two hours

Processing modality

Individual specimen

May use pooled samples depending on disease incidence and samples

Individual specimen

Each rapid antigen test is a single test on a single individual

Individual specimen

This is dependent on what rapid system is used and how it is used

Individual specimen

Applications

Gold standard for diagnosis

Pooled sample testing can be considered for  individuals/where prevalence is low.

For screening, many publications recommend a twostep screening strategy: rapid antigen testing as a first diagnostic method followed by RT-qPCR to distinguish false from true positives.

Repeated mass antigen testing can temporarily reduce the number of new infections. For lasting effects, re-testing at regular intervals would likely be necessary.  The benefits of testing tend to be small in low-prevalence settings.

For screening, many publications recommend a twostep screening strategy: rapid antigen testing as a first diagnostic method followed by RT-qPCR to distinguish false from true positives.

Communicable Disase Network Australia (CDNA) and Public Health Laboratory Network (PHLN) recommends preserving laboratory-based serology tests for where the result will influence individual patient or outbreak management.

In the US, CDC suggest a two-step testing algorithm, in which an initial positive test is confirmed by a second, different antibody assay.

Table two - Test samples

 Saliva Respiratory specimensSerum

Collection method

Different collections methods reported including:

Nasopharyngeal, oropharyngeal and nasal swabs

Fingerpick blood test

Self-collection

The sensitivity of a self-saliva sample was inferior by 9.5% compared to a healthcare work swab. Sensitivities up to 95% reported.

Sensitivity for detecting SARS-CoV-2 in patient collected (compared to professionally collected) tongue, nasal, and mid-turbinate samples was 89.8%, 94.0% and 96.2% respectively.

Sensitivity depends upon the collection methods and device.

High percentage (97-99%) able to self-collect an adequate sample

Sensitivity

85%

97% (nasal and throat swab)

86% (nasal swab)

68% (throat swab)

Specificity depends upon the collection methods and device.

The combination of IgG/IgM:

30% (for 1 to 7 days)

72% (for 8 to 14 days)

91% (for 15 to 21 days)

Specificity

99%

99% (nasal and throat swab)

99% (nasal swab)

97% (throat swab)

98%

Test mechanism

RT-PCR

Isothermal nucleic acid amplification tests e.g. LAMP

Infrared light technology

Lateral flow

Rapid antigen tests

Rapid molecular tests

RT-PCR

Isothermal nucleic acid amplification tests e.g. LAMP

Lateral flow

Rapid antigen tests

Rapid molecular tests

Antibody tests

Lateral flow immunoassay technology

Table three - Policy

 NSWAustraliaNZUKUSACanada

Preadmission hospital/surgery

NSW does not recommend routine COVID-19 testing pre-operatively for elective surgery patients.

Routine preoperative testing is not recommended in patients with no risk factors.

Routine preoperative testing is not recommended in patients with no risk factors.

Self-test 3 days before the day of your procedure.

Patients should undergo nucleic acid amplification testing (including PCR tests) prior to undergoing non-emergent surgery.

For paediatric patients, all patients and their caregivers should be assessed for risk factors and symptoms prior to surgery, and should be tested if there are any symptoms of contact with a confirmed COVID-19 case.

Routine testing population

Testing is recommended for anyone who has: any COVID-19 symptoms; visited a place or travelled on public transport at the same time as a confirmed COVID-19 case; been at an interstate COVID-19 case location during a specific time period; been in contact with a confirmed COVID-19 case or a close contact of a confirmed COVID-19 case.

Anyone with even mild symptoms of respiratory infection should get tested.

Rapid antigen tests should not be used alone for diagnostic purposes.

Self-testing is prohibited in Australia.

People with any COVID-19 symptoms should be assessed and/or tested based on symptoms and circumstances.

Anyone who does not have symptoms can get regular rapid lateral flow tests to check for COVID-19.

Self-testing is used in the UK.

Rapid, regular community testing program for asymptomatic individuals was rolled out across England. Testing was targeted at people unable to work from home during lockdown.

Screening tests are recommended for unvaccinated people to identify those who are asymptomatic and do not have known, suspected, or reported exposure to SARS-CoV-2.

Deciding who should be tested is based on symptoms, underlying medical conditions, and risk of exposure to COVID-19.

Routine testing staff

NSW quarantine worker surveillance and testing program with saliva testing.

Regular testing of asymptomatic staff working in COVID-19 quarantine and isolation settings is recommended. Large-scale, non-targeted asymptomatic testing is not currently recommended.

Rapid antigen tests will be performed onsite for selected workplaces and schools in NSW. The Therapeutics Good Administration has approved 20 rapid antigen tests for use in Australia.

Regular, mandatory testing for border workforce groups.

Targeted asymptomatic testing of primary health providers only on advice from Ministry of Health and/or public health unit.

Private-sector employers are recommended to offer their on-site staff access to a minimum of two lateral flow tests per week.

Point-of care testing in residential aged care facilities assists identification of infection in residents and staff.

Testing asymptomatic healthcare workers without known or suspected exposure to SARS-CoV-2 is recommended for workers in nursing homes. Testing asymptomatic healthcare workers who do not work in nursing homes may be considered if resources are available.

No real-world evidence to support or refute, the potential harms and costs outweigh the benefits for long term care staff.

Background

The Royal College of Pathologists of Australasia highlights that rapid antigen tests have lower sensitivity and specificity and therefore should never be used alone for diagnostic purposes. They may need to be used for surveillance purposes in circumscribed agreed settings in COVID-19 hotspots.

Point-of-care testing may not necessarily be constituted by ‘close to patient’ ‘easy use’ or ‘simple platform’ devices. Rapid output devices are usually cartridge-based tests that can only be run serially on one instrument and take the full onboard run time for analysis. For example, a one-hour test takes one hour for one test after which you can run another one-hour test on another patient.

Lateral flow devices are a form of testing for SARS-CoV-2 which rely on the detection of viral antigens by immunoassays.

Some rapid diagnostic tests may lead to high rates of false negatives and false positives.

A Cochrane review on rapid antigen tests identified virtually no evidence for mass screening of asymptomatic individuals using rapid antigen tests in people with no known exposure, and no evidence of test accuracy in at-risk asymptomatic groups. Using data for the most sensitive assays in symptomatic people (SD Biosensor STANDARD Q and Abbott Panbio), at 5% disease incidence prevalence, between 1 in 10 and 1 in 6 positive results will be a false positive and between 1 in 4 and 1 in 8 cases will be missed. At 0.5% prevalence, applying same tests in asymptomatic people, rapid antigen test would result in 7 in 10 and 9 in 10 positive results being false positives, and between 1 in 2 and 1 in 3 true positives being missed.

Rapid antigen tests have been implemented across a variety of settings including: frontline screening at emergency departments, mass gathering live music event, hospital admission, schools, screening test for travellers, points of entry, targeted testing to release individuals from unnecessary quarantine, and targeted testing in outbreak settings.

The benefits of screening with rapid antigen testing is proportional to disease prevalence, with greater benefit from higher community risk.

Limitations

Different testing protocols are used throughout the literature, as well as differing definitions of what constitutes a rapid test. Some publications did not include in their results how long the test took. Implications of self-collection of tests, including the potential implications to public reporting of cases, are not explored in this review.

The methods for recording or interpreting the results of these tests may be rudimentary and often manual with no electronic repository available for collection or documentation into any patient result record. The expectation that these tests can be done at volume is not necessarily accurate given the manual requirements necessary.

Many studies are product specific and heterogeneous performance may limit our ability to assess the efficacy of the generic approach.

Sensitivity and specificity rates were taken from Cochrane reviews where available, otherwise recent systematic reviews and do not represent a full range as reported throughout the literature. In regards to rapid molecular tests, only tests evaluated in the published Cochrane review are included in this table.

Living evidence tables include some links to low quality sources and an assessment of the original source has not been undertaken. Sources are monitored daily but due to rapidly emerging information, tables may not always reflect the most current evidence. The tables are not peer reviewed, and inclusion does not imply official recommendation nor endorsement of NSW Health.

Last updated on 20 Sep 2021

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