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Larger households related to larger odds of SARS-CoV-2 transmission

As the coronavirus disease (COVID-19) pandemic continues to spread around the world, more information about the spread of the virus will be released. The transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the household has been classified as one of the main causes of the spread of COVID-19.

Secondary attack rates for household contacts are estimated to be five to 10 times higher than for contacts outside the household. However, it is unclear who among household members is more likely to spread the virus.

A research team from Public Health Ontario and the Sunnybrook Research Institute now wanted to determine the factors that influence the transmission of the coronavirus in the household. Specifically, the researchers wanted to compare the characteristics of cases in households with secondary transmission with those that did not.

The team found that longer testing delays and masculinity were associated with a higher risk of secondary household transmission. Households with more family members are also more likely to be affected by the spread of COVID-19.

The study

The study published on the medRxiv * preprint server shows how household transmission is contributing to the growing number of coronavirus cases, which has now exceeded 43.89 million worldwide.

Based on the address match, the team identified all households with confirmed SARS-CoV-2 infections from Ontario in Canada from January to July in order to arrive at the study results. The researchers compared the characteristics of cases in households with secondary transmission with those without. To obtain the data, they used the provincial reportable disease systems entered by local health authorities.

Secondary transmission occurs when cases occur 1 to 14 days after the first person is identified with the coronavirus. The team used the symptom onset date or the sample collection date. Additionally, in the study they considered a wide range of individual and neighborhood covariates related to household transmission.

The line represents the direction of transfer from the index case to the secondary case. The line shadow represents the age group or risk group of the index case. The line width is proportional to the frequency of transmission between index and secondary cases in their respective age or risk groups. Years = years

Study results

In total, more than 38,000 confirmed COVID-19 cases have been reported in Ontario. After some cases were removed based on the inclusion criteria, the team lived in more than 26,000 households. Of these, more than 18,000 cases were from households with no secondary transmission and more than 7,900 cases were from households with secondary transmission.

The team found that longer testing delays and masculinity contributed to a higher risk of secondary transmission in the home or apartment. On the flip side, being in health care or being associated with a known outbreak was associated with lower household transmission chances.

The team also found that neighborhoods with a larger average economic family size and a higher percentage of people living in a room were associated with higher chances of household transmission. This means that the more people live in a house, the higher the risk of a COVID-19 outbreak in the household.

“Our results of a higher likelihood of multi-person household transfer between neighborhoods and multi-family households might support this hypothesis, and our relationship with economic family size might capture aspects of neighborhood overcrowding.” Team explained.

Household transmission plays a crucial role in the spread of SARS-CoV-2. The study recommends that people need testing immediately or as soon as symptoms appear. In this way, they take precautions to protect the other family members.

“Ideally, people should be tested on the day they started having symptoms, as a day’s delay was associated with an increased likelihood of secondary transmission. If cases live with other people, it can also be important to try to isolate in a room alone or outside the house if possible, ”the researchers said.

These mitigation strategies can be considered by public health officials to combat household transmission. Further studies should be done to investigate the role of children and adolescents in household transmission.

The coronavirus pandemic has now killed more than 1.16 million people. The United States remains the hardest hit country, reporting more than 8.77 million cases, followed by India with a staggering 7.94 million people.

* Important NOTE

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.


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