Just 262 cases traced to outdoor activities since pandemic began, official figures reveal
Prof Mike Weed from the University of Canterbury, who studied 27,000 Covid-19 cases, says outdoor gatherings are safe if accompanied by proper risk management. File photograph: iStock
Just one confirmed case of Covid-19 in every thousand is traced to outdoor transmission, new figures reveal.
Of the 232,164 cases of Covid-19 recorded in the State up to March 24th this year, 262 were as a result of outdoor transmission, representing 0.1 per cent of the total.
There were 42 outbreaks associated with outdoor gatherings, with one community outbreak accounting for seven cases.
This involved an outdoor work activity which took place between two separate families, according to the Health Protection Surveillance Centre (HPSC) which monitors case numbers in the Republic.
There were 21 outbreaks on construction sites with 124 cases, and 20 outbreaks associated with sporting activities and fitness in which there were 131 cases.
The HPSC data, provided in response to a query from The Irish Times, was based on “locations which are primarily associated with outdoor activities, ie outdoor sports and construction sites, or outbreaks that specifically mention in comments that an outdoor location or activity was involved”. The HSPC said, however, that it “cannot determine where transmission occurred”.
In addition 20 per cent of all cases in the State result from community transmission where the source of the infection is not known.
The relatively low numbers of cases resulting from outdoor transmission in the Republic is mirrored in international studies. A study of 1,245 cases in China found only three people were infected outdoors and they were in conversation without masks. According to a review by the University of California of five global studies of transmission, the chances of getting Covid-19 in an indoor setting is 19 times greater than outdoors.
At the University of Canterbury, Prof Mike Weed studied 27,000 Covid-19 cases based on 6,000 different pieces of data. One study was of 7,500 cases in China and Japan before lockdown in both of those countries. The number of cases associated with outdoor transmission was “so small to be insignificant”, he discovered.
Prof Weed said outdoor gatherings are safe if accompanied by proper risk management. For example, crowds could be allowed at sporting events if rules are observed around congregating in indoor venues beforehand.
“Our conclusion is that in many sectors, and for many sizes and formats, it should be possible to put appropriate evidence-based mitigations in place to deliver outdoor events and activities in a way that does not escalate the risk from sporadic transmission to cluster outbreak,” he said.
Ed Lavelle, a professor of biochemistry at Trinity College Dublin, said the findings were “really great news and back up a lot of the evidence from the United States” which showed that outside activities are inherently safe.
He added that the big issue was not the outdoor activity, but what happened either side of it.
“We have not had the numbers until now for what is safe and what is not safe and how you can control it. It’s been hearsay to this point,” he said. “Having coffee shops outside would be very safe. For me, the key thing is what happens after the outdoor activity.”
Assistant professor at University College Dublin’s school of architecture Prof Orla Hegarty said it is difficult for the HPSC to measure outdoor transmission as construction and sport can be both outdoor and indoor.
She said outdoor risk is low “if people keep physical distance, avoid close conversation and take great care that shared transport and shared toilets are very well ventilated – and that they stay a very short time and wear masks in them.
“During Spanish flu people were advised to talk side by side, rather than face to face, and this is borne out by how viral particles have been measured moving in the air when people breath and speak.
“The risk of infection is low outdoors because unless you are up close to someone infected, most of the virus will likely be blown away and diluted in the breeze, like cigarette smoke.”