Question: What do we know about transmission risk in outdoor settings? We’ve been doing a lot more of seeing our friends in socially distanced, outdoor spaces because we know it’s safer than indoors. Even so, how much are we chancing it?

Answer: The more we know, the more we can be confident that: a) outdoor settings are much, much safer than indoor settings; and b) outdoor settings do not erase risk. Even when socializing outdoors, we need to take precautions, including by keeping our distance (6+ feet). The good news is that — to my knowledge — we do not have any evidence of transmission in the context of outdoors + socially distant. If you’re abiding by these parameters (and staying home if unwell, washing hands too), I think your risk is very low.

We talked about indoor/outdoor risk in our Q&A of 5/20 and 5/12. Over the last two months, we don’t (to my knowledge) have much rigorous science on outdoor transmission risks a la the study out of China that we discussed in our Q&A of 5/12. What we have now is a lot of news reports indicating where clusters of infections originated. We also have this database of literature and media reports, “COVID-19 Settings of Transmission”, compiled by researchers at the London School of Hygiene and Tropical Medicine and further described in their article, “What settings have been linked to SARS-CoV-2 transmission clusters?” I just became aware of this open access database last night and I admit, I am really excited to access it (nerd!)! Mind you, a database like this has a lot of limitations; but in the context of limited and emerging data, it’s a helpful resource. So here’s our outdoor transmission risk update:

• Of the total 266 cluster events compiled as of 6/7, only 7 were fully outdoors — 4 cluster events at building sites in Singapore, 1 at a seafood market in China (discussed in Q&A of 5/12), 1 at a playground in Germany. and 1 from a running partner in Italy. Note: 20 events of the 266 were in indoor/outdoor spaces.
• The most common cluster settings captured in the database are: households, large shared accommodation settings (e.g. dormitory, lodge, group home), sports settings, religious settings (e.g. indoor church services), food processing plants, and elder care settings (Table 1 and Figure 1).
• There are several events not yet captured in the database that are relevant. Last week, the New York Times provided a nice synthesis, including reports of COVID transmission at a DC socialite’s backyard soiree. And at the beginning of July, the Times reported that recent protests had not caused a wave in infections, “In Minnesota, an initiative that targeted demonstrators found that 1.5 percent of them tested positive. In Massachusetts, fewer than 3 percent of protesters did.”

Table 1. Cluster Settings (from COVID-19 Settings of Transmission Database)

Figure 1. Case Clusters by Setting and Size (from ScienceNews)