COVID-positive people spread the infection to others at home 53% of the time

If someone in your household tests positive for COVID-19, there is a 53 percent chance they will pass it on to you or someone else living under your roof, a new Centers for Disease Control and Prevention (CDC) finds. 

And the transmission rate was similar regardless of whether the first coronavirus patient was an adult or child. 

Prior research has found that a person is more likely to catch coronavirus at home than in other locations such as stores or public transit. 

But the CDC authors also warn that rates of secondary infections are higher in the US than in other nations where people are more consistently isolated within or outside their homes, or where families are more likely to wear masks at home. 

People who have coronavirus pass it to other members of their households about 53% of the time, no matter how  old the first patient is, the CDC found (file) 

The CDC closely tracked 101 Americans who tested positive for coronavirus and 191 people who lived with them. 

People between 18 and 49 were most likely to be the index patients – the first infected – and primary infections were least common among children younger than 12. 

Young children represented just five percent of all index patients, and people aged 50 and older made up 41 percent of cases. 

Nearly a quarter (22 percent) of the index patients had some form of underlying condition. Asthma was the most common, with 23 percent of initial coronavirus patients suffering the common respiratory condition.  

More importantly, 19 percent of all household members of initial coronavirus cases had underlying  conditions that might make them more vulnerable to infection and severe COVID-19. 

Thirteen percent had asthma, seven percent had each heart disease and diabetes, one percent had kidney disease and two percent were immunocompromised or smoked. 

Most of the first cases in each household did not have symptoms when they tested positive, while  41 percent did. 

People who have symptoms likely have higher viral loads and are more infectious than asymptomatic people, though research suggests that people with no symptoms are anywhere between 25 and 75 percent as infectious as those  with symptoms. 

But within a week, 67 percent developed symptoms. 

In total, the virus was passed from the first case to at least one other household member in 53 percent of homes.  

Transmissions happened fast. Three-quarters of secondary infections happened within just five days of the first household member getting sick. 

The rate of transmission from children under 12 to other household members was even higher, at 57 percent. 

People aged  50 or older were actually least likely to pass coronavirus to a family member, which happened in 43 percent of cases. 

Young adults between 18 and 49 were most likely to infect another person in their household, transmitting the infection 59 percent of the time. 

‘Secondary infection rates were high across all racial/ethnic groups. Substantial transmission occurred whether the index patient was an adult or a child,’ the CDC authors noted. 

‘Other studies, particularly those conducted abroad, might have found lower secondary infection rates because of rapid isolation of patients in facilities outside households or different adoption of control measures, such as mask use, in the home.’ 

The CDC researchers urged that anyone who has tested positive for COVID-19 be isolated, preferably outside the home, but at least within it. 

What’s more, they underscored how frequently initial cases had no symptoms at  the time of the their positive tests, signalling that isolating as soon as there’s been a possible exposure might be wise to prevent the infection from spreading at home.