Characteristics and Timing of Initial Virus Shedding in Severe Acute Respiratory Syndrome Coronavirus 2, Utah, USA

Nathaniel M. Lewis; Lindsey M. Duca; Perrine Marcenac; Elizabeth A. Dietrich; Christopher J. Gregory; Victoria L. Fields; Michelle M. Banks; Jared R. Rispens; Aron Hall; Jennifer L. Harcourt; Azaibi Tamin; Sarah Willardson; Tair Kiphibane; Kimberly Christensen; Angela C. Dunn; Jacqueline E. Tate; Scott Nabity; Almea M. Matanock; Hannah L. Kirking


Emerging Infectious Diseases. 2021;27(2):352-359. 

In This Article


In our study, we found that symptoms of secondary SARS-CoV-2 infection occurred in 7 household contacts of index COVID-19 patients starting <2 days before and ≤3 days after the observed initiation of viral shedding. The median interval of 4 days between symptom onset in index patients and symptom onset in their respective SARS-CoV-2–positive household contacts was similar to that reported in other household studies.[10,11,15] Timely enrollment in our investigation (median 4 days after symptom onset in the index patient), however, allowed us to observe the timing and characteristics of initial viral shedding with a level of granularity not attained in previous studies.

For the household members (02–02 and 05-01) in whom we observed the initiation of viral shedding (i.e., SARS-CoV-2–positive result by rRT-PCR after a negative test), the first day of shedding corresponded with a high Ct value, and the second day of shedding corresponded with a lower Ct value, a positive viral culture, and the onset of new symptoms. These observations suggest that although the initiation of shedding marks the beginning of potential infectiousness, higher likelihood of virus transmission (indicated by positive viral culture) might coincide with lower Ct values and the appearance of additional symptoms.[16] Although 4 persons continued shedding virus >12 days after onset of symptoms, no culturable and potentially infectious virus could be isolated from the specimens collected.

For the 2 household members (02-01 and 02–03) in whom we observed presymptomatic viral shedding, initial shedding corresponded with medium or high Ct values and occurred for 1–2 days before symptom onset. In 1 patient (02-01), the onset of symptoms coincided with a progression from high to medium Ct value, and new, additional symptoms coincided with further progression from medium to low Ct values. These findings mirror previous observations of presymptomatic shedding but suggest that viral load might increase as symptoms appear or progress. Among all SARS-CoV-2–positive contacts, symptoms were generally mild and sometimes transient. Of note, only 4 of 7 cases reported classic lower respiratory symptoms. In HH-02, the 2 contacts (02-01 and 02–02) who reported lower respiratory symptoms had them at illness onset, alongside several other symptoms. In HH-05, of the 3 contacts who had lower respiratory symptoms (05-01, 05-02, 05-03), two (05-01 and 05-03) reported them several days after symptom onset. Reports of symptoms by household contacts who remained SARS-CoV-2–negative could suggest other viral illnesses, allergies, underlying medical conditions, or stress-related effects of living with a person with COVID-19.[17]

Our findings suggest that household-level isolation practices could have been effective in preventing transmission. Findings from the 2003 SARS-CoV-1 epidemic showed that isolation of a patient before peak shedding was effective in reducing household transmission,[18] and our results suggest that adopting precautionary measures can be effective in preventing secondary household transmission. In the households where no transmission was experienced, providing an index patient with separate sleeping quarters and avoiding face-to-face interactions (e.g., shared mealtimes) appeared sufficient to prevent transmission, even in households where close or intimate contact had occurred before diagnosis. Our findings show, however, that some persons infected with SARS-CoV-2 could begin shedding virus before being prompted to isolate by the onset of symptoms. In contrast to the households with no transmission, which consisted primarily of adults, the 2 households with secondary transmission to all contacts consisted of parents and their adolescent or preadolescent children. In these households, childcare needs and difficulties maintaining full isolation caused members to eschew precautionary practices, particularly after other household members were known to be infected.

Our study has some limitations. First, our household case-series was small because of the intensive nature of our early monitoring protocol; it was also biased toward index patients who were sufficiently symptomatic to be tested but whose disease was not severe enough to require hospitalization. Second, although all SARS-CoV-2–positive contacts had symptom onset ≥2 days (the estimated minimum incubation period) after the corresponding index patient, we cannot rule out the possibility of transmission from 1 presymptomatic household contact to another contact. Finally, symptom data relied on self-reporting, and symptoms might have been present before or after they were reported by patients. Three (20%) of 15 household contacts were children <13 years of age, who might have had more difficulty recognizing and reporting symptoms. Patient subjectivity could contribute to whether virus shedding or symptom onset is observed first.

In conclusion, our findings indicate that shedding of the SARS-CoV-2 virus might occur early in the disease course before symptom onset and clinical diagnosis, or it could occur when symptoms are mild or even absent. Persons with confirmed COVID-19 or who have had close contact with someone with confirmed COVID-19 should limit close contact with others, including household members, for 14 days. Persons who have been exposed to SARS-CoV-2 should be vigilant to the onset of mild symptoms; if they have not already limited close contact with household members or other persons, the onset of even mild symptoms should prompt additional caution and efforts to limit close contact. In addition, wearing masks or cloth face covers, practicing hand hygiene, and disinfecting surfaces regularly might reduce risk for transmission in households.[19] Stay-at-home orders and at-home self-treatment of COVID-19 in the United States requires clear communication of such guidelines to prevent household transmission.