Five months too late, modelers have finally realized that there is high degree of variability in susceptibility to infection by CV and in infectiousness. This paper is the latest in that line of research. (Medrxiv Paper) Without going into the math, the authors developed a model which incorporated persistent heterogeneity, which they attribute to social and biologic factors. Their conclusions were that such models, which likely are truer to life, have three major consequences: the early epidemic dynamics are different; the proportion of infected people to achieve population immunity is lower; and the total number of people infected is lower.
Continuing from a theme in the last post, this paper also relates to transmission and infection by the current coronavirus, in particular understanding why in some cases this one seems to result in more serious illness. (Medrxiv Paper) I am fascinated by the science of this and thinking about how infection actually occurs and what it means to be infected. The paper in the earlier post dealt with the virus’ progress in nasal passages and other parts of the respiratory tract and estimated a very low infectious dose. This paper explains why that may be. The researchers identified a simple mutation in this coronavirus strain’s RNA that appears to lead to binding with ACE receptors 100 times stronger than the binding of other coronaviruses. That means the virus is capable of remaining attached to a cell for a longer period of time, permitting entry into the cell where replication can occur. Another fascinating piece of research.
And another study relating to transmission, this one simulating the spread of aerosols by an infected person. (JAMA Study) This is not an actual experiment or even a quasi-experiment, more like a thought experiment. The setting was a closed room, not well ventilated, with an infected person and uninfected ones. A coughing infected person would put multiples of the virus into the room compared to a normally breathing person. They concluded that an infected person with a normal viral load just breathing even in their hypothetical space would pose a low infectiousness risk, but a cougher would pose a pretty high risk.
Seasonality or at least geographic variability seems to be a feature of the epidemic. Weather factors would be the logical suspect. This is another piece of research, from China, attempting to ascertain relationships between temperature, humidity and infections. (Medrxiv Paper) The researchers examined 1236 regions in the world, collecting weather data, information about their epidemic and socio-economic data. The conclusions were that for every 1 degree increase in temperature, daily cases would be down 2.88% six days later (presumably reflecting incubation period). And for every percentage point increase in relative humidity, cases would be down .19% six days later. I am not buying it, mostly because no one knows how many cases there are in any one place and testing and other factors don’t allow for some universal estimate across regions. So there is no accurate way to develop a relationship between cases and other factors across the world.
As we know here in Minnesota, properly counted, long-term care residences are the source of well over half of all CV fatalities in the country. This study looked at factors relating to the serious of the outbreak in various nursing homes. (JAMA Article) 23 states were included. There were not significant rating differences between facilities that did and didn’t have cases, in fact those with cases had slightly higher quality ratings on some measures. There also were not significant staffing differences. But there were more deficiencies cited at facilities with cases. Having more CV cases in the area was strongly associated with nursing home outbreaks. For-profits were more likely to have cases, as were facilities with a higher proportion of Medicaid patients.
This paper looked at prevalence of infection among health care workers in Houston. (JAMA Article) The study was conducted by a hospital concerned about asymptomatic workers. About 4% of staff tested positive, with a much higher rate among workers who actually were in contact with CV patients. All these infections were asymptomatic, again pointing to the need for regular testing of health care workers to limit spread to patients or other staff.