Symptom-Based Screening May Fail to Identify all SARS-CoV-2 Infections

Unrecognized asymptomatic and presymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections might contribute to transmission in long-term care facilities.

Unrecognized asymptomatic and presymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections might contribute to transmission in long-term care facilities, according to study results published in the Morbidity and Mortality Weekly Report.

In order to evaluate the utility of symptom screening for identification of coronavirus disease 2019 (COVID-19) in residents of a skilled nursing facility in King County, Washington, researchers categorized 82 residents as asymptomatic or symptomatic based on the presence or absence of fever, cough, shortness of breath, or other symptoms on the day of testing or during the preceding 14 days.

Following a positive test result in a healthcare provider, 76 of 82 residents were tested for SARS-CoV-2 using reverse transcription–polymerase chain reaction (RT-PCR) with 23 having positive test results. The demographic characteristics were similar between those who tested positive and negative for COVID-19.

Among the 23 residents with positive test results, 10 (43.5%) were symptomatic, and 13 (56.5%) were asymptomatic. Eight residents had typical COVID-19 symptoms, and 2 had only atypical symptoms; the most common atypical symptoms reported were malaise (n=4) and nausea (n=3).

Seven days after testing, 10 of the 13 previously asymptomatic residents developed symptoms upon re-evaluation and were recategorized as presymptomatic on the day of testing, reducing the percentage of asymptomatic infections down to 13% (3 of 23). The mean interval from testing to symptom onset in the presymptomatic residents was 3 days. The most common signs and symptoms that developed were fever (n=8), malaise (n=6), and cough (n=5).

Real-time RT-PCR testing cycle threshold values indicated large quantities of viral RNA in asymptomatic, presymptomatic, and symptomatic residents, suggesting the potential for transmission regardless of symptoms. The range for both genetic markers (N1 and N2 nucleocapsid protein gene regions) were as follows:

  • Symptomatic with typical symptoms: 18.6 to 29.2.
  • Symptomatic with atypical symptoms: 24.3 to 26.3.
  • Presymptomatic: 15.3 to 37.9.
  • Asymptomatic: 21.9 to 31.0.

There were no significant differences between the mean cycle threshold values in the 4 symptom status groups (P =.3).

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“Although these findings do not quantify the relative contributions of asymptomatic or presymptomatic residents to SARS-CoV-2 transmission…they suggested that these residents have the potential for substantial viral shedding,” noted the researchers. Further, if asymptomatic or presymptomatic individuals play a central role in the transmission of SARS-CoV-2, the researchers highlighted that additional measures for prevention, such as increased screening and implementing transmissions-based precautions should be considered. They recommended that once a confirmed case is identified in a nursing home facility, all residents be placed on isolation precautions if possible, with considerations for extended use or reuse of personal protective equipment during the current COVID-19 pandemic.


Kimball A, Hatfield KM, Arons M, et al; Public Health – Seattle & King County; CDC COVID-19 Investigation Team. Asymptomatic and presymptomatic SARS-CoV-2 infections in residents of a long-term care skilled nursing facility – King County, Washington, March 2020. MMWR Morb Mortal Wkly Rep. 2020;69(13):377-381.