Covid-19 Antigen

1. General

Diagnostic tests are a key element of disease control strategies around the world. RT-PCR test that directly detects the presence of the virus in the human body is considered the “Gold Standard Test” in coronavirus diagnosis. After the pandemic starts, test strategies around the world have been predominantly based on RT-PCR, however, after the availability of Ag-RDT for diagnostics, many countries around the world have incorporated antigen testing into their
respective testing strategies for disease mapping purposes.

Pakistan’s current testing strategy relies solely on RT-PCR testing and has worked well (played a critical role in disease control worked well until now). However, since Ag-RDT has been shown to be effective for disease mapping, therefore, Pakistan has considered incorporating Ag-RDT into its testing strategy for disease surveillance and put it on screen.

2.Rapid antigen detection test (Ag-RDT)

“Rapid antigen tests are commonly used in the diagnosis of respiratory pathogens, including influenza viruses and respiratory viruses. Ag-RDT is widely used throughout the world for diagnose SARS-CoV-2 ”. Ag-RDT has certain advantages, such as relatively lower cost and returns results in about 15 minutes, etc.

3 Guidelines for use

a. WHO

  • Respond to suspected outbreaks in remote settings, institutions, and semi-closed communities.
  • Ag-RDT could be used to detect high-risk individuals, isolate positive cases, and PCR for prioritized negative individuals.
  • Monitor trends in disease incidence in communities and essential workers, health workers during outbreaks or in extended community regions transmission.
  • A negative Ag-RDT should not remove a contact from quarantine requirements.

B. CDC THE US

  • FDA granted Emergency Use Authorization (EUA) to use Ag-RDT to comply with claim tests.
  • Antigen tests work best if a person is tested in the early stages of infection.
  • Can be used for screening in high-risk collective environments.
  • The performance characteristics of Ag-RDT to give false negative results must be accounted for in the actual evaluation.

C. European CDC

  • Rapid antigen tests can contribute to overall COVID-19 testing capabilities by offering advantages in terms of shorter response times and reduced costs, especially in situations where the RT-PCR testability is limited.
  • The sensitivity of the test for rapid antigen tests is generally lower than for RT-PCR.
  • Rapid antigen tests work best in cases with high viral load, in presymptomatic patients, and early symptomatic cases up to five days from the onset of symptoms.
  • The ECDC is in accordance with the minimum performance requirements established by the WHO at ≥80% sensitivity and specificity ≥97%.
  • ECDC recommends that the EU Member States carry out independent and environment-specific validations of rapid antigen tests prior to implementation.
  • The use of rapid antigen tests is appropriate in high-prevalence settings when a positive result is likely to indicate a true infection, as well as a low prevalence environment to quickly identify highly infectious cases.
  • Rapid antigen tests can help reduce transmission through early detection of highly infectious cases, allowing a quick start of contact tracing

4. Test strategies around the world

The large Ag-RDT is used worldwide to complement PCR-based tests and to accurately map the disease. It is mainly used in high-risk sectors.

5. Global Trends Conclusions

  • Given the massive spread of COVID-19, worldwide PCR testing capacity is emphasized, therefore, many countries (including the USA, UK, Germany, France, Italy, Canada, and regional countries, etc.) are incorporating Ag-RDT into the disease mapping strategy.
  • WHO and CDC have recommended the use of Ag-RDT for high-risk groups, communities, high transmission areas, large surveys, and screening.
  • Ag-RDT is used in combination with the PCR test. Due to its false negativity aspects, RT PCR is mandatory for all Ag-RDT negative symptomatic cases.

6. Justification of Ag-RDT in Pakistan

Based on the global experience of employing Ag-RDT in disease mapping, Pakistan (after an extensive consultative process) has decided to adopt rapid antigen testing to improve disease mapping and to complement PCR-based tests, but under strict control/monitoring. This will expand the number and scope of tests, especially in certain defined environments.

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