Another paper looks at infection rates among homeless and similar populations, this time in Marseille, France. (Medrxiv Paper) About 700 people were tested. 49, or 7%, tested positive on an infection test. No antibody test was performed. About half had no typical symptoms of coronavirus disease.
A Lancet article describes the results of an attempt in China to actively track transmission of 391 cases. (Lancet Article) The cases occurred in one city. Some were identified from symptom-based surveillance and some by monitoring of close contacts. Symptomatic persons were treated; asymptomatic ones were quarantined in a facility. 77% of cases were identified by surveillance. Only 9% of cases were deemed severe. The incubation period was around 4 to 8 days. The median time to recovery was 21 days. 1286 close contacts of these cases were tested and followed. 98, or around 7%, were ultimately infected. Household contacts were most likely to become infected. Children appeared equally likely to become infected after contact as did adults, but had far less severe illness. The elderly had higher infection rates. Each infected person on average only infected one-half additional person. It is notable that even in households, less than one in six contacts became infected. There was a wide dispersion in infectiousness, in other words, some infected individuals didn’t infect any one else and some infected several people.
An analysis of asymptomatic transmission on the Diamond Princess was performed in another recent paper. (Medrxiv Paper) The cruise ship received a lot of attention early in the epidemic because it was kind of a natural laboratory for the epidemic’s features. One of the most notable things was how few people actually became infected in such a closed environment. There also were many asymptomatic cases. This paper focused on the role of the asymptomatic group in transmitting infections. About 75% of cases on the ship were asymptomatic and those individuals were estimated to be responsible for transmitting 69% of all new cases. The crew had an average age of 36 and was estimated to have 89% asymptomatic cases. The passengers had an average age of 69 and 42% of those cases were asymptomatic. So in a heavily elderly population, with extensive exposure, there was both a low rate of infection and a high rate of asymptomatic cases. Ongoing evidence supports this as features of the epidemic.
And I ran across some data from Arizona, which apparently is doing antibody and infection testing. (Ariz. Data) The infection testing isn’t much use, because unless everyone is being tested, you have to assume it is mostly people who have a symptom or who were in contact with someone who did. But the serology testing is finding 3.3% positive so far. These are likely people who didn’t get sick and seek infection testing, but I don’t know the state’s exact strategy. In any event, that 3.3% of the entire population would be about 219,000 people, once again far more than the number reported by infection testing alone, which is only about 11,300 cases.