Latest Coronavirus Science: How Covid-19 Spreads in a Family

Illustration for article titled Latest Coronavirus Science: How Covid-19 Spreads in a Family
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Here’s our roundup of the latest developments and research into covid-19, including more evidence of racial disparities during the pandemic, the possible higher risks from for-profit nursing homes, and Brazil’s worsening disaster.


How coronavirus spreads in a household

A new study in BMJ Global Health is one of the first to provide current evidence of whether face masks can prevent the transmission of covid-19 between people who live together. Researchers in China studied over 120 families in Beijing with at least one member confirmed to have the coronavirus, encompassing a total of 335 people.

Between February 28 and March 27, an additional 77 people in the study contracted the virus. Within families, though, certain interventions may have prevented its further spread. The daily use of chlorine or alcohol-based disinfectants in the home, for instance, was linked to a 77 percent lower chance of secondary infection. The odds of infection were 18 times higher if someone reported frequent daily contact with the infected person. Keeping windows open and staying 1 meter apart were also linked to reduced spread of the virus in families.

Family members regularly wearing masks at home was linked to a 79 percent lower chance of infection, but only if the mask-wearing began before the first infected person began showing symptoms. The study was retrospective, meaning that the researchers had to rely on people’s recollections, which can be flawed. But as they point out, it’s seemingly the first real-world evidence of the “effectiveness of mask use, disinfection and social distancing in preventing covid-19.”

Interestingly, they also found evidence of fecal transmission, with the odds of family member infection being four times higher if the first sick person experienced diarrhea. Previous research has suggested that airborne poop particles could be a source of coronavirus infections.

The findings reinforce the benefits of “universal face mask use and social distancing, not just in public spaces, but inside the household with members at risk of getting infected.”


Nursing home disparities

Given the more serious effects of covid-19 on older people, nursing homes have unsurprisingly been a major source of severe cases and deaths. But a preliminary paper out this week suggests that for-profit nursing homes in Canada have been even deadlier for their residents.


The paper, released on the preprint website medRxiv, used government data on covid-19 cases and deaths to compare how all nursing homes in Ontario have fared during the pandemic. In total, they looked at 623 nursing homes, over half of which were for-profit.

Between March 29 and May 20, there were 5,218 nursing home covid-19 cases and 1,452 deaths in the area. For-profit homes, the study found, weren’t more likely to have an outbreak than nonprofit homes or those run by the local government. But they were more likely to have larger outbreaks with more deaths.


The study’s findings haven’t yet gone through peer review, so they should be taken with caution. But if accurate, then it suggests there are added risk factors that can endanger nursing home residents.


When the authors tried to find possible explanations for the difference between for-profit and nonprofit homes, they only found one: The for-profit homes were more often made with older, outdated building design standards. These standards, which tend to include fewer single-resident rooms, smaller rooms in general, and shared bathrooms, likely offered more opportunities for the virus to spread between residents and staff members. The more open and private spaces seen with newer design standards, the authors wrote, “beyond promoting quality of life, are designed to promote infection prevention and control.”

Covid-19’s racial gap

A new study published this week in the New England Journal of Medicine highlights the racial gap of the pandemic so far in the U.S.


Doctors examined cases from a single health care system that covers much of Southeast Louisiana. Black people represented about 31 percent of the population covered by the system’s hospitals and medical centers, but between March 1 and April 11, they accounted for 70 percent of all confirmed covid-19 cases that passed through the system (over 3,500 in total), as well as 77 percent of hospitalizations.

Black people were also more likely to die from covid-19 than white patients. Their higher mortality rate was linked to risk factors like the severity of their illness upon admission, pre-existing conditions, and other sociodemographic indicators, like whether they lived in a low-income neighborhood.


The findings suggest, as other research has, that black people have been especially vulnerable to catching covid-19 and that they’re worse off once they do. People of color disproportionately work in service jobs and other businesses that have been deemed essential during the pandemic that expose them to the virus. Black people are also more likely to develop health problems that could increase the risk of severity from the coronavirus, such as diabetes or heart disease.

As many natural disasters before it, covid-19 seems to have only widened the existing cracks of inequality in our society.


Brazil’s growing tragedy

Earlier this week, the U.S. passed the ignoble milestone of 100,000 confirmed covid-19 deaths (the true death toll likely surpassed that number a while back, if excess death data is accurate). But though the U.S. has certainly failed on multiple fronts in dealing with covid-19, it isn’t the only country to bungle its response.


New projections this week from the Institute for Health Metrics and Evaluation (IHME), based at the University of Washington, predict that Brazil will have around 125,000 documented deaths by August, far surpassing the likely death toll of its neighbors.

IHME’s projections, particularly in the U.S., have been criticized for underestimating deaths. But its more recent projections have been in line with other existing models, and the recipe for Brazil’s disaster seems well in the making.


With over 400,000 reported cases, the country now has the second-largest outbreak in the world, and its daily reported death toll (over 1,000 on Wednesday) has started to sometimes beat that of the U.S., home to the world’s largest outbreak. Much like Donald Trump, Brazilian president Jair Bolsonaro has regularly dismissed the seriousness of the pandemic, and the country has struggled to provide enough testing and resources to its doctors and hospitals. Bolsonaro has promoted the use of chloroquine as a cure for covid-19, now considered an ineffective treatment by many experts.

Another model devised by independent data researcher Youyang Gu and others, which has been especially accurate so far, predicts that Brazil will have around 195,000 deaths by September. Not to be outdone, though, the same model predicts that the U.S. will reach 200,000 deaths by then as well.


Science writer at Gizmodo and pug aficionado elsewhere


Fabian Knockwurst

This (excellent) post and several others suggest that there’s a virus concentration threshold aspect to the spreading of Cov-SARS-2. That is, we might imagine that one viable virus (particle) will suffice, but there are numerous subsequent steps (non-specific (non-antibody) immune system defenses, for example) which make a single virus infection unlikely. The dynamics seem to be: exposure to a large initial dose and you get a life threatening pathology (nursing homes, meat processing plants, hospital workers); exposure to a small dose and you might only vaguely notice it. Here’s hoping someone is examining whether bolting on a concentration threshold might make the pandemic statistics even more accurate. (dosis facit venenum? the dose makes the poison)