The study, which was conducted by CDC researchers between April and September, analyzed data from 191 household contacts and 101 COVID-19 patients in Nashville, Tennessee, and Marshfield, Wisconsin. Researchers trained the original patients and members of their household to complete symptom diaries and collect their own nasal swabs or nasal swabs and saliva samples for 14 days.
No household contacts reported having symptoms when the original patient in their home became sick. But, after a follow-up period, 102 of the household contacts tested positive for SARS-CoV-2, the virus that causes COVID-19. That created a 53% secondary infection rate—the rate of spread of the virus within a small unit, like a home.
“Understanding how transmission occurs in households and how frequently it occurs will provide significant information regarding SARS-CoV-2 transmission dynamics and provide best practices to prevent outbreaks, particularly in close-contact settings,” Jill E. Weatherhead, MD, MS, DTMandH, FAAP, assistant professor of infectious diseases at the Baylor College of Medicine in Texas, tells Verywell.
Household Transmission Rates
A secondary infection rate “represents the likelihood of an infected individual transmitting the virus to another person,” Weatherhead says. “It provides scientific data on how social interactions impact transmission rates.” Secondary infection rates aren’t unique to COVID-19. They’re also used to detect the spread of other infectious diseases.
The secondary infection rate for original patients over 18 was 57% and subsequently fell to 43% when the original patient was under 18. It’s worth noting, though, that 20 of the original patients were children compared to 82 adults.
Less than half of household members who developed COVID-19 also had no symptoms when they were first diagnosed. Many also did not report symptoms during the seven days of their follow-up care.
Experts say a lot can be gleaned from this information. “This particular article demonstrates that transmission largely occurs within five days of the index patient’s illness onset and both adults and children are able to transmit the virus to other household contacts,” Weatherhead says.
Most households had one person per bedroom. Nearly 70% of original patients said they spent four or more hours in the same room with one or more members of their household the day before they were diagnosed, and 40% reported the same the day after their symptoms developed.
The data clearly shows that, if someone develops symptoms of COVID-19, they should self-isolate “immediately” to try to prevent the spread to other household members, Weatherhead says. The study suggests self-isolating at the onset of symptoms, at the time of resting as a result of high-risk exposure, or at the time of a positive test result, depending on which comes first.
The reports underscore how highly contagious COVID-19 is, Richard Watkins, MD, an infectious disease physician in Akron, Ohio, and a professor of medicine at the Northeast Ohio Medical University, tells Verywell. “It’s easily transmissible, especially when people are in prolonged close contact,” he says. “This is why it’s important for family members to not get infected in the first place.”
Weatherhead says that household spread of COVID-19 isn’t inevitable, but it is common. “This is due to the sustained close-contact, indoor space, and shared resources that occur in households,” she says.
Next Steps If a Household Member Is Infected
If a member of your household contracts COVID-19, Weatherhead says they should self-isolate, and that the members of your household quarantine. The CDC recommends that you and your family do the following:
If possible, have the sick person use a separate bedroom and bathroom. Try to stay at least six feet away from your sick household member. If you need to share space, make sure the room has good airflow. Encourage the sick person to eat separately from other household members, and handle any utensils they use with gloves. Wash your hands regularly. Do not share personal items, including towels, bedding, and phones. Wear a mask and gloves when caring for the sick person, and have them wear a mask when others are around. Clean and disinfect high-touch surfaces like doorknobs and faucets daily. Wear gloves when handling laundry and avoid shaking it. Track your own symptoms.
“If feasible, only one person should care for that sick individual,” Weatherhead says.
The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.
