Implications of Shortened Quarantine Among Household Contacts of Index Patients With Confirmed SARS-CoV-2 Infection

Tennessee and Wisconsin, April-September 2020

Melissa A. Rolfes, PhD; Carlos G. Grijalva, MD; Yuwei Zhu, MD; Huong Q. McLean, PhD; Kayla E. Hanson, MPH; Edward A. Belongia, MD; Natasha B. Halasa, MD; Ahra Kim, MPH; Jennifer Meece, PhD; Carrie Reed, DSc; H. Keipp Talbot, MD; Alicia M. Fry, MD

Disclosures

Morbidity and Mortality Weekly Report. 2020;69(5152):1633-1637. 

In This Article

Abstract and Introduction

Introduction

To prevent further transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), CDC currently recommends that persons who have been in close contact with someone with SARS-CoV-2 infection should quarantine (stay away from other persons) for 14 days after the last known contact.* However, quarantine might be difficult to maintain for a prolonged period. A shorter quarantine might improve compliance, and CDC recommends two options to reduce the duration of quarantine for close contacts without symptoms, based on local circumstances and availability of testing: 1) quarantine can end on day 10 without a test or 2) quarantine can end on day 7 after receiving a negative test result. However, shorter quarantine might permit ongoing disease transmission from persons who develop symptoms or become infectious near the end of the recommended 14-day period. Interim data from an ongoing study of household transmission of SARS-CoV-2 were analyzed to understand the proportion of household contacts that had detectable virus after a shortened quarantine period. Persons who were household contacts of index patients completed a daily symptom diary and self-collected respiratory specimens for 14 days. Specimens were tested for SARS-CoV-2 using reverse transcription–polymerase chain reaction (RT-PCR). Among 185 household contacts enrolled, 109 (59%) had detectable SARS-CoV-2 at any time; 76% (83/109) of test results were positive within 7 days, and 86% (94 of 109) were positive within 10 days after the index patient's illness onset date. Among household contacts who received negative SARS-CoV-2 test results and were asymptomatic through day 7, there was an 81% chance (95% confidence interval [CI] = 67%–90%) of remaining asymptomatic and receiving negative RT-PCR test results through day 14; this increased to 93% (95% CI = 78%–98%) for household members who were asymptomatic with negative RT-PCR test results through day 10. Although SARS-CoV-2 quarantine periods shorter than 14 days might be easier to adhere to, there is a potential for onward transmission from household contacts released before day 14.

A CDC-supported study of household transmission of SARS-CoV-2 is currently ongoing in Nashville, Tennessee, and Marshfield, Wisconsin.[1] Household contacts of an index patient who had symptoms compatible with COVID-19 for <7 days and laboratory-confirmed SARS-CoV-2 infection were eligible for the study if they had not had symptoms of an acute respiratory illness up to the date of the index patient's illness onset.§ Enrolled household contacts were instructed to self-collect respiratory specimens (nasal swab only or nasal swab and saliva) and complete a daily symptom diary for 14 days. The study protocol was reviewed and approved by the Vanderbilt University Medical Center's and Marshfield Clinic Research Institute's Institutional Review Boards and was conducted consistent with applicable federal law and CDC policy.**

For each household contact, the number of days from the index patient's illness onset to 1) the day of first positive test result, 2) the day of first symptoms, or 3) the end of the follow-up period, whichever occurred first, was calculated. Survival analysis, accounting for left-censoring,†† was used to estimate the conditional probability that a household contact who was asymptomatic and whose specimens tested negative for SARS-CoV-2 by RT-PCR through day 5, 7, or 10 would remain asymptomatic and negative through day 14. Sensitivity analyses were conducted, excluding households with possible co-primary patients (households with household contacts who had illness onset or positive test <2 days after the index patient's illness onset) and household contacts with possible tertiary transmission (household contacts who had a positive test >2 days after another nonindex household contact had a positive test result).

During April–September 2020, among 105 index patients, 185 household contacts were enrolled (median of one household contact per index patient, interquartile range [IQR] = 1–2; 45% of household contacts were male; median age of household contacts = 27 years, IQR = 15–45 years). Enrollment occurred a median of 4 days (IQR = 2–4 days) after the index patient's illness onset and study follow-up concluded a median of 16 days (IQR = 15–17 days) after the index patient's illness onset. Overall, 109 (59%) household contacts had SARS-CoV-2 detected in respiratory specimens during the follow-up period, with the first positive specimen collected a median of 5 days (IQR = 3–7 days) after the index patient's illness onset. Among all infected household contacts, 76% (83 of 109) had infection detected within 7 days after the index patient's illness onset and 86% (94 of 109) within 10 days.

The probability that a household contact who was asymptomatic and had negative RT-PCR test results through day 7 would remain asymptomatic with negative RT-PCR test results through 14 days after the index patient's illness onset was 81% (95% CI = 67%–90%); the probability increased to 93% (95% CI = 78%–98%) if the household contact remained asymptomatic with negative test results through day 10 (Table). After excluding 22 households (including 45 household contacts) with possible co-primary index patients and 10 infected household contacts with possible tertiary transmission, the conditional probability that the contact would remain asymptomatic with negative RT-PCR test results through day 14 was 95% (95% CI = 81%–99%) if the person was asymptomatic and negative through day 10.

*https://www.cdc.gov/coronavirus/2019-ncov/if-you-are-sick/quarantine.html.
https://www.cdc.gov/coronavirus/2019-ncov/more/scientific-brief-options-to-reduce-quarantine.html.
§Index patients (or their parent/guardian) were asked "Have all other members of their household had fever, cough, cold, or other respiratory symptoms?" [Marshfield, Wisconsin site] or "Has anyone in your home, besides you, been sick with a fever, cough, cold, or flu-like symptoms in the 7 days before your illness began?" [Nashville, Tennessee site]. If the response was yes, the household was ineligible to participate.
The following signs and symptoms were solicited from participants on the daily diary: fever/feverishness, cough, sore throat, runny nose, trouble breathing or shortness of breath, nasal congestion, chills, fatigue or feeling run down, wheezing, chest tightness or chest pain, abdominal pain, diarrhea, vomiting, headache, muscle or body aches, and loss of taste or smell.
**45 C.F.R. part 46.102(l)(2), 21 C.F.R. part 56; 42 U.S.C. Sect. 241(d); 5 U.S.C. Sect. 552a; 44 U.S.C. Sect. 3501 et seq.
††Household contacts who had positive SARS-CoV-2 RT-PCR test results on the date of enrollment were considered left-censored because the date of initial infection was not observed during the study period.
§§ https://www.cdc.gov/coronavirus/2019-ncov/hcp/faq.html#Transmission.

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