Trying to understand who is at most risk for serious illness and hospitalization is important both for the management of care for those patients and for estimating the potential burden on the health care system. Several papers have looked at characteristics of patients who end up hospitalized for coronavirus illness and they generally come to similar conclusions. This paper comes from a group of researchers across the US who looked at over 5000 hospitalizations. (Medrxiv Paper) The risk of being hospitalized was higher for obese persons, those with chronic kidney disease, diabetes, hypertension, or asthma. In addition, those over age 65, males and minorities had a higher adjusted risk.
A similar paper comes from a UnitedHealth Group division that examined about 17,000 hospitalizations. (Medrxiv Paper) 75% of hospitalized patients were over age 50, 72% were obese, 58% had hypertension, 23% ended up in the ICU, 18% were ventilated, and 16 died. Average length of stay was 6 days. 71% had pneumonia at some point during the admission.
Another piece of research, this time from Spain, that identifies potential antibodies against the current strain of coronavirus from prior infections. (Medrxiv Paper) The researchers developed a new assay, that they claim is more sensitive. The assay could detect antibodies against the receptor binding domain, the spike protein and the nucleocapsid protein. The assay was tested against 43 patients who were hospitalized and 50 persons who had not been infected. In a number of the non-infected persons, the assay detected antibodies to the nucleocapsid protein of the current strain. The authors interpreted this as cross-reactivity from prior infection by seasonal coronaviruses.
I don’t always report on antibody prevalence studies, but this is one of the first I have seen from Africa. (Medrxiv Paper) Coming from Kenya, over 3000 persons were included, and on a population-characteristics-adjusted basis, prevalence was estimated about 5.2% nationally, with larger percents in more urbanized areas. This is hundreds of times the reported number of infections in the country. Most of these cases would be asymptomatic. Africa has a young population, so this is what we would expect.
Another antibody survey comes from Pakistan. (Medrxiv Paper) This was a randomized household survey in Karachi, and was conducted in two phases. By the later phase, prevalence was estimated at about 8.7% to 15.1%, even in areas that reported low levels of cases. This is another younger population, and almost all the positive tests, 95%, were asymptomatic cases.
This paper looked at prevalence among a group of health care workers in Spain. (Medrxiv Paper) The prevalence of antibodies was estimated at 19% and 68% of those were asymptomatic cases. This suggests the importance of regular testing of health workers, as they could be infectious, but having no symptoms.
Another paper looking at transmission and infection dynamics, via a modeling exercise. (Medrxiv Paper) The author notes the three identified possible mechanisms for transmission–large droplets, smaller aerosolized particles or residues on surfaces, but also note that the first appears to be far and away the most significant. He next discusses what is an exposure, and what parts of the respiratory tract are most affected by exposure. Interestingly, cells along the nasal passage lining have higher susceptibility that do those cells in the the throat and bronchial lining, largely due to more ACE receptors, which are how the virus enters a cell. But the mucus layers in the nasal passage also provide some defense against infection. The author suggests that cells in the nasal passages are unlikely to be infected but can be the source of seeding an infection lower down by inhalation of virus. Particle sizes and breathing rates are considered for effect on transmission of virus and CT scans of two healthy individuals’ nasal areas were used to model the dynamics of potential virus travel into and through the nose to other parts of the respiratory tract. Based on the author’s calculations of droplet size, number of droplets over a period of time of exposure and other factors, he estimated an infectious dose could be as small as 300 virions or even less. That is a small dose. He also finds a significant potential affect of humidity on droplet size and number of virions. Finally, note that the droplet size estimates and number of virions constituting an infectious dose support the likelihood for ineffectiveness of masks.