This morning’s New York Times roundup, by David Leonhart, mentioned a blog post by a Dartmouth biologist, Erin S. Bromage: The Risks – Know Them – Avoid Them.\u00a0 <\/a>It is an excellent explanation of the role of time, airflow, viral density in spread of disease. A little math, lots of science and some references to serious papers. It contains some very practical information: basically, avoid enclosed spaces where you might spend time with other people. Worth a read.<\/p>\n

Here are some excerpts:<\/p>\n

\u00a0 \u00a0 Indoor spaces, with limited air exchange or recycled air and lots of people, are concerning from\u00a0a transmission standpoint. We know that 60 people in a volleyball court-sized room (choir)\u00a0results in massive infections.\u00a0Same situation with the restaurant and the call center.\u00a0\u00a0Social\u00a0distancing guidelines don’t hold in indoor spaces where you spend a lot of time<\/strong>, as people on\u00a0the opposite side of the room were infected.<\/p>\n

The principle is viral exposure over an extended period of time. In all these cases, people were\u00a0exposed to the virus in the air for a prolonged period (hours). Even if they were 50 feet away\u00a0(choir or call center), even a low dose of the virus in the air reaching them, over a sustained\u00a0period, was enough to cause infection and in some cases, death.<\/p>\n

Social distancing rules are really to protect you with brief exposures or outdoor exposures. In\u00a0these situations there is not enough time to achieve the infectious viral load when you are\u00a0standing 6 feet apart or where wind and the infinite outdoor space for viral dilution reduces viral\u00a0load.<\/p>\n

\u2026 When assessing the risk of infection (via respiration) at the grocery store or mall, you need to\u00a0consider the volume of the air space (very large), the number of people (restricted), how long\u00a0people are spending in the store (workers – all day; customers – an hour). Taken together, for a\u00a0person shopping: the low density, high air volume of the store, along with the restricted time\u00a0you spend in the store, means that the opportunity to receive an infectious dose is low. But, for\u00a0the store worker, the extended time they spend in the store provides a greater opportunity to\u00a0receive the infectious dose and therefore the job becomes more risky.<\/p>\n

\u2026 Basically, as the work closures are loosened, and we start to venture out more, possibly even\u00a0resuming in-office activities, you need to look at your environment and make judgments. How\u00a0many people are here, how much airflow is there around me, and how long will I be in this\u00a0environment. If you are in an open floorplan office, you really need critically assess the risk\u00a0(volume, people, and airflow). \u2026\u00a0If you are sitting in a well ventilated space, with few people, the risk is low.<\/p>\n

…If I am outside, and I walk past someone, remember it is \u201cdose and time\u201d needed for infection.\u00a0You would have to be in their airstream for 5+ minutes for a chance of infection.<\/p><\/blockquote>\n

 <\/p>\n

Be careful out there.<\/p>\n","protected":false},"excerpt":{"rendered":"

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