August 26, 2020


Earlier this week, the US CDC published a major update to its SARS-CoV-2 testing guidance. The biggest change addresses asymptomatic individuals with known exposure to a COVID-19 case. In the previous version of the testing guidance, the CDC recommended diagnostic testing for, among others, “asymptomatic individuals with recent known or suspected exposure to SARS-CoV-2 [in order to] to control transmission.” In the current iteration, the CDC states that asymptomatic individuals who have close contact with a COVID-19 case “do not necessarily need a test unless [they] are a vulnerable individual” or if it is recommended or required by their healthcare provider or local or state public health agency. Notably, testing guidance published on other sections of the CDC website, updated on the same date as the testing guidance described above, continues to include close contact with a known case as a principal consideration for testing, along with exhibiting COVID-19 symptoms and referral by healthcare providers or public health officials.

The recommendation that asymptomatic individuals with known exposure do not necessarily need to be tested has potentially serious implications for both COVID-19 control and surveillance. The updated guidance does recommend that these individuals monitor for symptoms, but as we have covered previously, it is widely understood that individuals infected with SARS-CoV-2 can transmit the infection without exhibiting symptoms—either in the days prior to the onset of symptoms or without developing symptoms at all. In fact, the CDC’s own “current best estimate” indicates that 50% of SARS-CoV-2 transmission occurs prior to the onset of symptoms (presymptomatic transmission) and that asymptomatic individuals are still 75% as infectious as symptomatic cases. Further down in the new testing guidance, at the bottom of the page, the CDC explicitly notes that infected individuals can spread the virus to others while they are not symptomatic, but the guidance does not provide further information regarding self-quarantine or other measures to mitigate this risk. Without testing, asymptomatic individuals would have no way of knowing that they are infected and potentially placing others at risk. Considering the significant role of asymptomatic and presymptomatic transmission, it is unclear why the testing guidance would de-emphasize testing any individuals with known exposure.

The new testing guidance also states that asymptomatic individuals with known exposure “should strictly adhere to CDC mitigation protocols”; however, it is not clear exactly to which protocols the guidance is referring. The CDC guidance on community-related exposures recommends that exposed individuals self-quarantine for 14 days, monitor for fever and other symptoms, and avoid higher-risk individuals, but there is no link to this information from the new testing guidance. It is possible that the CDC wholly shifted its focus to self-quarantine following all known exposures, at least for asymptomatic individuals, rather than waiting for or relying on diagnostic test results; however, this is not all that clear from reading the updated testing guidance alone. Individuals seeking information on testing would also need to know where else to look in order to get the full set of recommendations.

Regardless of whether quarantine without testing would be sufficient to contain the spread of COVID-19—including whether exposed individuals would voluntarily self-quarantine in the absence of both symptoms and a positive test—the change could also impact public health COVID-19 surveillance. The CDC guidance notes that state and local health departments may require testing for asymptomatic individuals with known exposure, but the change in guidance could have a substantial impact on the volume of testing conducted for these individuals, particularly for those not already known to health officials (eg, through contact tracing). A spokesperson for the Department of Health and Human Services argued that the updated guidance functions to support public health surveillance at the state and local levels. Public health officials have struggled since the onset of the pandemic to characterize the scale of infection in their communities, particularly with respect to asymptomatic infections or mild cases. If asymptomatic individuals with known exposure are no longer recommended for testing, this could limit the number of infections reported to public health agencies and prioritize those with more severe disease, much like what occurred early in the pandemic. This has potentially serious implications for our understanding of the level of community transmission as well as disease severity and mortality risk. Notably, the CDC guidance for schools repeatedly emphasizes the need to understand and control community transmission in order to mitigate transmission risk as students return to in-person classes. Without testing asymptomatic individuals with known exposure, it could give the false impression that community transmission is lower than it actually is, which could subsequently increase the risk for school-based transmission, clusters, and outbreaks.