Diagnostics Global… Implementation

Implementation

In the following, we would like to show possible scenarios for implementing an antigen rapid diagnostic test (Ag-RDT). Further details can also be found in the national testing strategy, published by the Robert-Koch-Institute.

The strengths of Ag-RDTs lay in their rapid turn-around time and limited infrastructure requirements. The main disadvantages are lower accuracy compared to a PCR test and a lower throughput (i.e. one person can only perform one Ag-RDT at a time). Thus, an Ag-RDT is best suited for screening sequential people for infection and identifying those with a high viral load, which indicates a high risk for transmission. PCR testing is still preferred over an Ag-RDT when possible due to its higher accuracy, particularly in settings where a person is symptomatic and entering a high-risk environment.

For concrete scenarios to implement an Ag-RDT, two important aspects need be taken into account. First, the likelihood that the individual to be tested is SARS-CoV-2 positive. The best way to define this pretest probability is by the patient’s symptoms: a symptomatic person has a higher pretest probability than an asymptomatic person. Furthermore, the risks of potential transmission due to a missed diagnosis should be considered; these mainly depend on the health status of potential contacts and the possibility of a superspreading event.

Based on the above mentioned, an Ag-RDT could be implemented in the following three scenarios.

Scenario 1:

Pretest probability: low (i.e. an asymptomatic person).

Risk after potential transmission: high, due to contact with persons whose age or comorbidities place them at risk of severe of COVID-19 disease and/or due to a high risk of intense transmission (i.e. superspreading event).

Likely contexts:

  • visitors to nursing homes or hospitals
  • staff in nursing homes, practices or hospitals (should ideally be tested daily)
  • events with >10 persons in one room lasting >1 hour

Advantages of using an Ag-RDT: quick decisions for isolation, protection of high-risk patients

Disadvantages of using an Ag-RDT: costs for testing every person, false sense of security from a negative result

Scenario 2:

Pretest probability: low (i.e. an asymptomatic person).

Risk after potential transmission: very high, due to contact with persons whose age or comorbidities place them at risk of very severe COVID-19 disease.

Possible context:

  • Admission of patients without COVID-19 symptoms to nursing homes
  • Admission of patients without COVID-19 symptoms to a hospital’s geriatric or hematologic/oncologic unit
  • For both contexts, ideally a PCR test should be performed in parallel with the Ag-RDT and repeated on the fifth day after admission

Advantages of using an Ag-RDT: quick decisions for isolation, protection of high-risk patients

Disadvantages of using an Ag-RDT: costs for testing every person, false sense of security from a negative result

Scenario 3:

Pretest probability: high (i.e. a symptomatic person).

Risk after potential transmission: high, due to contact with persons whose age or comorbidities place them at risk of severe COVID-19 disease.

Possible context:

  • Admission of COVID-19 symptomatic patients to a hospital
  • Wherever possible, a PCR test needs to be performed in parallel. In case of continuing symptoms, the Robert-Koch-Institute’s recommendations for COVID-19 symptomatic patients should be followed

Advantages of using an Ag-RDT: quick decisions for isolation, protection of high-risk patients

Disadvantages of using an Ag-RDT: costs for testing every person, false sense of security from a negative result