By Kevin Roche
Well, so far in Florida, people seem to be going about their daily lives fairly normally. Appalachicola, which is a cute little tourist town, and Port St. Joe, were quite busy. A lot of virus refugees looking for that normality, it appears. Not a lot of masking, some stores and restaurants require them but haphazardly, and one restaurant that was quite insistent in its signs about how important masking was, had the greeter and the staff wearing them below the nose. It is interesting, however, how easily we become conditioned and indoctrinated by state-sponsored messaging because your natural reaction is to be fearful, even if you know they don’t really make any difference in stopping community spread.
An excellent study in Nature focused on the duration of infectiousness. (Nature Article) The study was done in the Netherlands on 129 hospitalized CV-19 patients. Only 23 of these patients had viable virus shedding by culture testing. These were patients who obviously had serious disease, yet even among them the median duration of shedding of viable virus was 8 days. The likelihood of finding viable virus was substantially higher in patients with higher viral loads based on PCR testing. When translated to cycle numbers, infectious virus was very unlikely to be found at cycle numbers above 30, or even 25.
Transmission rates were highest from adults to each other and adults to the elderly and vice versa. Transmission was low in schools, restaurants and bars. It was high in nursing homes.
This is kind of an interesting paper from Japan trying to estimate differences in the reproductive number by age and age group interactions. (Medrxiv Paper) This is essentially a measure of infectiousness. Children had very low reproductive numbers, i.e., transmission, even to other children. The elderly had very high ones, especially to each other. Transmission rates were highest from adults to each other and adults to the elderly and vice versa. Transmission was low in schools, restaurants and bars. It was high in nursing homes. The locations of transmission were diffuse, with only home being a high specific location.
And this is a similar study also from Japan. (Medrxiv Paper) The authors used contact tracing to identify patterns of transmission among age groups. Here is the crux, out of almost 27,000 cases in only 3240 could the source and nature of transmission be identified. Similar to the study above. So much for the value of contact tracing. Children were very unlikely to transmit to other children or the elderly and somewhat more likely to transmit to adults, usually parents. Adults were most likely to transmit to other adults, and most unlikely to transmit to children. The elderly were most likely to transmit to adults and other elderly persons. Almost all transmission in this study occurred among adults and the elderly.
And here is another study finding great variability in infectiousness, this time from Denmark. (Medrxiv Paper) The authors found that 10% of the infected population is likely responsible for 70% to 87% of spread. Most infected people don’t transmit to anyone. Another reason contact tracing is kind of pointless.
And this study examined differences in viral load by age. (Medrxiv Paper) Over 200,000 patients tested by PCR in the Netherlands were used for comparison of viral load, inferred by cycle number. Children under 12 had an average 16 times lower viral load than did the oldest group, those over age 79. This difference persisted across the spectrum of illness. Children were also much more likely to have positives with cycle numbers over 30. This may be an explanation for why children play a limited role in transmission.
Here is another paper attempting to identify CV-19 diagnostic test validity. (Medrxiv Paper) The authors did a metareview of other studies. The most important finding is that there was inadequate information to make a judgment on the performance of the tests in an asymptomatic population. This is buttressed by the tables showing the difference in performance in a low versus high prevalence population. If you are testing in a population where the true prevalence is 1%, the tests are all very inaccurate. Yet that is just what we are using them for, doing all kinds of ridiculous testing in people with no symptoms.
More interesting research on the relationship between seasonal coronavirus infections and CV-19. (Medrxiv Paper) T cell responses were compared in health care workers and people living in the community, for both seasonal coronaviruses and CV-19. Health care workers in general had higher levels of reactivity to seasonal coronavirus, suggesting they may have stronger cross-reactive defenses against CV-19. Health care workers who did not have CV-19 infection had higher levels of seasonal coronavirus T cell reactivity. And they had more frequent responses to CV-19 than did community dwellers. Those HCW who had been infected by CV-19 had lower reactivity to seasonal coronaviruses, suggesting some interference. Antibody levels to seasonal coronavirus were similar across all groups. Overall the study does suggest that adaptive responses to seasonal coronavirus can aid in protecting agains CV-19.