FYI

Dear Marika,

Several of our International Task Force teams have consolidated responses to address your questions. Below you will find our suggestions and recommendations as well as several useful links to WHO and CDC COVID-19 guidance documents and review articles relating to various testing strategies and prioritization.

We hope this helps you in your decision making process, and please feel free to reach out with any additional questions or points of clarification.

Best,

Todd Davis

International Task Force Laboratory Team Lead

2019 Novel Coronavirus Response

Current testing strategy:  

Diagnostic: PCR test for all patients, who meet the covid-19 case definition and with fever and pneumonia.

Screening: IgM and IgG tests for all healthcare workers biweekly; if the test is positive – PCR.  

High risk groups are : healthcare workers, residents of long-term facilities, army and may be few more.  

We would like to have your suggestions and answers on the following questions:

• Should we test asymptomatic individuals from the high risk groups? Given the testing shortages that many laboratories are experiencing or are likely to experience in the future, we suggest you carefully consider use and numbers of PCR test kits/supplies needed to maintain capacity for testing symptomatic individuals. Your current approach to screening HCWs first by serological assays will certainly help you to conserve PCR testing supplies, but you may find that a high number IgM and IgG positive samples leads to an unsustainable number of PCR tests required for confirmation of active infections in sero-positive individuals. This strategy has the potential to significantly reduce the number of PCR tests that could be needed in the future for testing of symptomatic individuals that meet the COVID case definition.            

• If yes, please, let us know which ones should be prioritized? If asymptomatic individuals are tested, we recommend prioritization of HCWs followed by residents of long-term care facilities. Due to the high risk of exposure to HCWs and their capacity to enhance onward nosocomial spread, this group should be prioritized. While residents of long term care facilities may not be at as high a level for risk of exposure, onward transmission among these facilities could be mitigated by rapid identification of asymptomatic carriers. Testing of asymptomatic soldiers or other groups of individuals living in close contact may also be considered if the testing is used as a means to perform contact-tracing when outbreak clusters are identified, but is otherwise not recommended due to concerns about future PCR test capacity as mentioned above.          

• What method should be used for screening of  asymptomatic  individuals (PCR or serology)? PCR is the preferred method as the result will confirm active infection in both asymptomatic or symptomatic individuals quickly and help to mitigate nosocomial or other community-associated spread. Serological assays currently are not recommended for diagnosis of active infection. While serology can help you to rule out a previous infection, the result (even for IgM serology) would not directly confirm an active infection and would then require additional PCR testing for confirmation. The links below provide some additional recommendations and rationale for situational serological testing that may further help in your decision process.  

https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/testing.html

https://www.cdc.gov/coronavirus/2019-ncov/testing/serology-overview.html

https://www.cdc.gov/coronavirus/2019-ncov/covid-data/serology-surveillance/index.html (See Table addressing what questions serological testing can and cannot answer.)

https://www.cdc.gov/coronavirus/2019-ncov/hcp/non-us-settings/guidance-identify-hcw-patients.html

https://www.who.int/publications-detail/advice-on-the-use-of-point-of-care-immunodiagnostic-tests-for-covid-19-scientific-brief

Annals of Internal Medicine - https://annals.org/aim/fullarticle/2764737/diagnostic-testing-severe-acute-respiratory-syndrome-related-coronavirus-2-narrative (The figures in this paper help provide

a framework in how to approach testing and also some characteristics and limitations of existing molecular and serologic tests.)

• How often should we perform screening of asymptomatic individuals in the high risk groups? Once per week should be sufficient given the time interval suspected to be required for an individual’s antibody response to reach sufficient titers for detection. However, weekly testing of the same individual may utilize too many resources and reduced testing capacity over the long term. As more is learned about the optimal frequency of testing asymptomatic groups, we will let you know. As mentioned above, the frequency of testing should be considered based on availability of testing supplies and projections of your future lab capacity needs.    

• Would you suggest to use PCR tests for HCW screening instead of serology (IgM& IgG). If yes – how often. As discussed above, PCR is the preferred method to confirm an active infection and will more quickly allow you to mitigate spread by an asymptomatic carrier. If your lab capacity is not significantly reduced by implementing PCR testing of asymptomatic individuals, once per week testing of HCWs is suggested so that mitigation plans can be implemented quickly if an individual tests positive. As more is learned about the optimal frequency of testing asymptomatic groups, we will let you know. As mentioned above, the frequency of testing should be considered based on availability of testing supplies and projections on future lab capacity needs.    

• When the restrictions are lifted, should we start screening in other groups as well (e.g. media workers, supermarket staff, etc.)? Serological testing of asymptomatic individuals in specific sub-populations would be better suited when planning community-based seroprevalence studies, but not as a screening tool to identify asymptomatic cases. Currently, the data from serologic testing appears to be more informative at the population level when used to assess the prevalence of past infection among groups, rather than at the individual level. Because we currently do not know about the implications of immunity among individuals or sub-populations, we encourage more sub-population level seroprevalence studies to be conducted as long as current lab testing capacity is not adversely affected. More information is needed to understand how serologic data can be used to assess population-level exposure and protective implications of population immunity, so we hope these studies can be conducted in the future.