RIO DE JANEIRO, BRAZIL – The word ‘cold’ is misleading. It refers to the temperature, yet it is viruses (or bacteria) that cause infections, not the degrees marked on thermometers. Temperature can help, but it is not decisive for the spread of respiratory diseases; at least not directly. The key is that in winter we stay indoors longer.
Poorly ventilated rooms are the perfect breeding ground for colds and infections to concentrate and spread. This is also true for Covid-19, which has the outdoors as one of its main enemies, as evidenced by the findings on the SARS-CoV-2 coronavirus.
Many epidemiologists speak of a resurgence of the epidemic in the fall. The fact is that it can happen at any time, but in the summer it seems less likely, just as it is more difficult to get the flu at that time. Much has been speculated about how the heat could affect the spread of the virus, with no decisive conclusions, although tropical countries have shown that it is not a determining factor.
If many experts expect a trouble-free summer, that’s because people tend to spend more time outdoors.
“The old saying of opening windows so that air can flow is the best thing to [fight] the virus,” says Antoni Trilla, epidemiologist, and advisor to the Spanish government’s scientific committee. Since it remains in closed spaces, it is more likely that suspended particles will be concentrated and inhaled. “If we keep our distance outdoors, the chance of contagion is very, very low,” he says.
It’s all about probabilities. No matter how little one goes out, there is no such thing as zero risks. One could run into someone infected, inhale a droplet with the virus, and become infected. But the odds of this happening are remote. The risk of transmission increases the longer one is in contact with a patient, and the closer this contact is since the amount of virus inhaled influences the probability of contagion.
Studies conducted on contagion sites have shown that the vast majority of these occur indoors. Gwen Knight, from the Center for Mathematical Models for Infectious Diseases, has collected several scientific studies (and other publications). As researcher Luis Jimenez says, of the 188 outbreaks analyzed only seven (or 3.7 percent) had their origin in an exclusively open-air activity.
“From the perspective of the number of confirmed infections, outdoor cases relate to 150, while indoor cases relate to over 9,000,” points out Jiménez after analyzing the data.
Ildefonso Hernández, a professor and spokesperson for the Spanish Society of Public Health and Health Administration, said in all published studies that most outbreaks have exploded in closed spaces: homes, companies, restaurants, stores, religious temples, hospitals, hotels, funerals, conferences. “They can also occur in open spaces, but the risk is much lower,” he says.
Although the odds are lower, “they are not zero,” says María del Mar Tomás, a microbiologist with the Spanish Society of Infectious Diseases and Clinical Microbiology. “We shouldn’t relax outdoors either. The epidemic is much more under control, but we must be careful about the feeling that it has passed,” she says.
Potential for another outbreak
A good example of this is what occurred in Lleida, where a birthday party with 20 people caused an outbreak that could slow Spain’s progress to the so-called new normality. Had everything gone well, the next relaxation stage would come next Monday, something that now seems unlikely.
Tomás’ recommendation is not to neglect safety distances also in open spaces, but he believes it is better to hold meetings with family and friends outdoors rather than indoors and, if possible, with a reduced number of people.
“The home provides us with a sense of safety that can be treacherous. If we have a party at home, we may relax, abandon prevention measures and there may be a surprise”, he stresses.
Trilla urges everyone to benefit from the advantages of a country “where there is much life outdoors”. Because fall will come and we will lock ourselves up again. “The dry cold certainly doesn’t help, but the main risk is that we’ll be in enclosed areas, with little ventilation, where the chance of contagion is much higher,” he says.
Only 43 out of nearly 10,000 infections occurred outdoors
In Gwen Knight’s compilation of infection outbreaks, there are only two that actually relate to open spaces, as Luis Jiménez says: “One refers to Wuhan’s market, the virus’s possible origin (with 41 infections), and the other to two fellow joggers, in which extra circumstances increased the risk: prolonged proximity, coupled with talking and/or intense breathing”.
In total, there were 43 cases with some degree of certainty concerning contagion in outdoor environments out of almost 10,000 confirmed cases.
In the largest research on outbreaks in China, over 7,000 cases of infection were traced back to the source sites. “The vast majority occurred indoors and in transports. Only one case of outdoor contagion was detected, involving two people who met on the street and chatted for a while,” Jiménez says.
Source: El País