A quick note on grim milestones. Minnesota today has 564 deaths per million people. Sweden is at 633 per million. We are gaining far too rapidly. And while Wisconsin now has many more cases than Minnesota, its deaths per million, at 507, remain lower than Minnesota’s. But everyone has a long way to go to match the disasters that are New York and New Jersey. I would encourage you to look at the worldometers site or covid tracking occasionally and you can see different country or state curves and raw and per capita numbers.
On to my never-ending attempt to keep up with the research. As usual I try to focus on items that tell us something about the virus, about how and when it is transmitted and on the effect of the mitigation measures which have been attempted. Also I think it is obviously very important to understand the adaptive immune response. I completely avoid pure epidemic course modeling papers at this point unless one is very innovative and shows a clear ability to accurately track the true past course of the epidemic. So I am n0t reading every single study out there, but I try to at least skim abstracts of as much as I can and pick out what I think will be most informative for understanding the big picture.
A very interesting study from Nature exploring spread in the epidemic’s putative start point, Wuhan, China. (Nature Study) Between May 14 and June 1 an attempt was made to PCR test every resident of the city in an effort to avert a second wave. Almost 10 million people were tested. No symptomatic cases were found and only 300 asymptomatic ones, which stayed asymptomatic. Among over 1000 contacts of these asymptomatic positives, not one secondary transmission was identified. 107 of the positives were people who had previously been identified as infected. Very likely that some of the initial positives or some of the ones in this study were false positives. Antibody testing was positive for 63% of these cases. All the positives were cultured and no viable virus was found. The median cycle number on the PCR positives was 35, so a lot of low positives. Older people were more likely to be among the few who tested positive. The study suggests that there can be a lot of asymptomatic people who have low levels of infection and aren’t infectious.
It is a sensible theory to suggest that greater community spread can result in spread inside more limited residential facilities, probably from contact with staff, visitors, new patients transferred in (ask Gov. Cuomo about that, I think he is an expert) or even suppliers who come to the facility. Or it may yet turn out that this virus has some really unusual ability to remain viable floating around in the air on dust or other particles for some time. In any event, researchers in Canada looked for any temporal association between community case increases and those in nursing homes. (Medrxiv Paper) They found a pretty long lag of 23 days between community increases and nursing home outbreaks, which seems like an attenuated association. But they also determined that the greater the current incidence (new cases) in an area, the more likely there would be an LTC outbreak sooner.
The study assessed early chains of transmission in France. (Medrxiv Paper) Over 6000 contacts of 735 cases from early in the epidemic were traced. The secondary attack rate was only 4%, but it increased with the age of the infector and/or infectee. Family contacts were at highest risk, accounting for almost half of identified transmission pairs. Over-dispersion was again a factor, with an estimated 10% of cases accounting for 80% of onward transmission. There were very few index cases in children.
The next study also comes from Canada and looked at the role of school closures. (Medrxiv Paper) The authors were prompted by the possibility that Canada might close schools again to examine whether that would really make a difference in case levels. Compared to other mitigation measures, they found that any effect of closing schools would be small. Most cases relating to schools were actually acquired in the community. And they noted the damage done to children from not being in school. This was a modeled study using historical data.
This is a pretty interesting study from India looking at transmission by people who died of CV-19 disease. So very sick people who were probably quite infectious. The study was somewhat small, 28 families, but the secondary attack rate was only 25% in the household, which is surprising given the severity of the infection in the index case. (Medrxiv Paper)
This is an interesting study sent by reader SD which dealt with the impact of the epidemic on nations, especially less developed countries. (Frontiers Article) The authors assessed five domains for each country, including demography, public health, economy, politics and meteorological factors, and assessed associations with CV-19 mortality. Country latitude, mostly temperate latitudes in each hemisphere, were associated with mortality, as surprisingly were several factors found in wealthier countries, such as stagnant life expectancy, greater metabolic disease burden and income. Stringency of mitigation/suppression measures were not associated with lower mortality.