Covid-19 patients infect half of households: US government study


People who develop Covid-19 infect about half of their household members, with adults being slightly more likely than children to spread the virus, a US government study said on Friday.

© Kevin C. Cox
A sign with the logo of the Centers for Disease Control and Prevention at the Tom Harkin Global Communications Center in Atlanta, Georgia

The Centers of Disease Control and Prevention (CDC) document is the latest to attempt to quantify the rate of transmission of the disease in households, with previous research varying widely but generally suggesting that adults are more important drivers than children.


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The new research conducted by the CDC consisted of finding cases of “index” or initial patients with lab-confirmed coronavirus infection in Nashville, Tennessee and Marshfield, Wisconsin, starting in April 2020.

The index patients and their household members were remotely trained to complete symptom diaries and obtain self-collected samples, which were either nasal swabs only or nasal swabs and saliva samples, for 14 days.

A total of 191 household contacts enrolled out of 101 index patients reported having no symptoms on the day of their index patient’s disease onset.

During the follow-up period, 102 of 191 contacts tested positive for SARS-CoV-2, for a “secondary infection rate” of 53 percent.

The secondary infection rate when the index patients were over 18 was 57%, which fell to 43% when the index patient was under 18.

Overall, there were significantly fewer child index patients than adults: 20 versus 82, which makes it more difficult to generalize the results for those under 18.

In terms of household characteristics, the median number of members per room was one, 69% of index patients reported spending four hours or more in the same room with one or more household members the day before and 40% the day after start of disease.

Forty percent of index patients reported sleeping in the same room with one or more household members before illness onset and 30% after illness onset.

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– Higher than reported –

Interpreting the results, the authors of the article wrote: “In this ongoing prospective study which includes systematic and daily follow-up, transmission of SARS-CoV-2 among household members was common and infection rates were secondary. were higher than those previously reported. ”

“Substantial transmission has occurred, whether the index patient is an adult or a child,” they added.

Another important finding from the study was that less than half of household members with confirmed infections reported symptoms by the time the infection was first detected, and many reported no symptoms for seven. follow-up days.

This highlights the potential for transmission from asymptomatic secondary contacts.

Other studies carried out abroad have sometimes found lower household infection rates.

The CDC said that could be because these studies did not have enough follow-up, or because these patients isolated in facilities outside their homes or enforced stricter use of masks.

He recommended that people who think they might have Covid-19 isolate themselves from other members of their household, including sleeping separately and using a separate bathroom if possible, and wearing a mask.

Exposed persons should not delay isolation until their infection is confirmed by testing.

A major limitation of the study was that determining who the index patient was can be difficult.

When the calculations were changed to exclude 54 household members who tested positive on the samples taken at the time of enrollment, but whose results took some time to be confirmed, the overall rate of secondary infection fell. at 35 percent.

However, it is still believed that the person who developed the first symptoms is the index patient.

ia / jh

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