COVID-19 Spread Fast Within Households in 2020 — From Children and Adults Alike

How often does COVID-19 spread inside a home, and how fast? Earlier estimates varied widely, and there was little data on spread from children. A CDC-supported study in Nashville, Tennessee, and Marshfield, Wisconsin, followed households closely from April to September 2020.

How the study worked

• The index patient was the first person in a household with COVID-19–like symptoms and a positive RT-PCR test, living with at least one other person.
• Households joined within 7 days of the index patient's illness; the median index patient was enrolled 4 days after getting sick.
• Everyone kept symptom diaries and collected their own nasal swabs (and sometimes saliva) daily; the first 7 days of samples were tested.

The analysis covered 101 households — 101 index patients and 191 household members who had no symptoms when the index patient fell ill. Index patients' median age was 32 (range 4–76); 14 were under 18.

Contact was close: 69% of index patients spent more than 4 hours in the same room as someone else the day before they got sick, and 40% shared a bedroom before their illness began.

What it found

• About 75% of infections were found within 5 days of the index patient's first symptoms.
• Spread was high in every racial and ethnic group, and substantial whether the index patient was a child or an adult.
• Only 40% of infected household members had symptoms when first found positive; over the week, 67% reported symptoms — so many infections were silent, underscoring the need for quarantine.

These rates were higher than many earlier estimates, perhaps because of this study's daily testing — or because studies elsewhere isolated patients outside the home or used masks more at home.

What to do

Because household spread is common and fast:

• Isolate right away — at the first symptoms, when you're tested after a high-risk exposure, or on a positive test, whichever comes first — rather than waiting for results. Stay home and use a separate bedroom and bathroom if you can.
• Everyone in the home, including the sick person, should wear a mask in shared spaces.
• Household contacts should quarantine as much as possible, stay away from people at high risk, and get tested.

Catching infections before symptoms would take frequent, fast community testing; the study aims to inform when and how often to test.

Limits: others may have been infected at the same time as the index patient; some infections may have come from outside the home; samples were self-collected; and the families may not represent the U.S. population.

Sources

Based on Carlos G. Grijalva, Melissa A. Rolfes, Yuwei Zhu and colleagues, "Transmission of SARS-COV-2 Infections in Households — Tennessee and Wisconsin, April–September 2020," MMWR, volume 69, Centers for Disease Control and Prevention; a work of the United States government in the public domain.