respiratory disease meteorological conditions

The risk of respiratory disease is directly related to meteorological conditions. The core triggering factors are temperature amplitude, relative humidity, wind speed, and concentration of air pollutants. When any two of the three conditions are met: the 24-hour temperature drop is ≥8°C, the relative humidity is <40% or >90%, and PM2.5 exceeds 75 μg/m³ for 2 consecutive days. The risk of illness for sensitive groups such as the elderly, children, and patients with basic respiratory diseases is 3.2-7.5 times higher than under suitable meteorological conditions.

I don’t say this out of thin air. In the past two years, I followed the meteorological and epidemiological investigation team of the city’s disease control and conducted community sentinel surveillance for half a year. The more than 2,000 cases of data in my hands can basically correspond to this threshold. Last week, on the day when Beijing experienced a sharp drop in temperature, I was checking Moments and saw three friends who work in pediatrics shouting at the same time, "The number has been scheduled for next week." I checked the weather data for that day: it dropped by 11 degrees Celsius in 24 hours, the relative humidity was 32%, and the PM2.5 concentration was 89 μg/m³. All three triggering conditions were met, and the explosion of numbers in the respiratory department was completely expected.

In fact, in the early years, the academic community had quite a divided understanding of this issue. One group insisted on "dominance of a single factor." For example, many old textbooks said that "sudden temperature drops are the primary cause of respiratory diseases." When I first entered the disease control internship, my teacher also told me that as long as the forecast temperature drops by more than 10 degrees, sentinel monitoring manpower must be prepared a week in advance. But later, as more and more monitoring data were collected, everyone gradually discovered that something was wrong - it was also a 10-degree drop in 24 hours. If the humidity on that day was around 50% and PM2.5 was still low, the number of cases would not increase at all. Instead, it would be the "three consecutive hits" of cooling, dryness, coldness, and haze that would really poke a hornet's nest of respiratory diseases.

For example, our respiratory mucosa is like the insulation layer of the exterior wall of our home. A sudden drop in temperature is equivalent to suddenly pouring a basin of ice water on the wall. Insufficient humidity will cause the wall to dry out and crack. Pollutants are dust stuffed into the cracks. If these three things are put together, the wall will not be damaged. What impressed me deeply was the "cold wave back to the south" in Guangzhou last November. The humidity was above 95% for the first three days, and the corridor walls were dripping with water. Then the cold wave came, and the temperature dropped from 28 degrees to 14 degrees in 24 hours. The wind was still very light, and there was pollution. The community health service center where I worked that week saw the number of upper respiratory tract infection cases increase by 4.2 times. The number of elderly people experiencing acute asthma attacks was more than three times that of the previous month. Many children who had never had allergies before were suffering from allergic coughs.

Many people think that dry cold is the biggest enemy. In fact, high humidity is not small at all. When the air humidity exceeds 90%, the particles of allergens such as pollen and dust mites will absorb water vapor and become heavier, making it difficult for them to float away. They will block the air at a height of 1 to 1.5 meters where people can breathe. In addition, mold spores can reproduce six times faster than in dry environments at this humidity, which is a strong source of irritation in itself. On the other hand, humidity lower than 40% is also troublesome. The layer of cilia on the respiratory mucosa is used to sweep out the incoming dust and viruses like a small broom. If the humidity is not enough, the swing speed of these small brooms will be directly reduced by half. The time the virus can stay on the mucous membrane can be tripled, and the probability of infection will naturally increase. Speaking of which, there is another interesting little discovery. When we collected data, we found that when there was a breeze of 2-3m/s for three consecutive days, the humidity was 50%-60%, and the temperature was 18-24 degrees, the number of respiratory tract consultations could be reduced to one-third of the usual volume. It is not an exaggeration to say that this is "magic weather".

There is also a school of research that has been raising the issue in recent years, saying that everyone previously underestimated the impact of wind speed. I used to think that the stronger the wind, the better, as pollutants will disperse faster. However, in fact, when the wind speed exceeds 5m/s, it will blow up all the pollen, dust, and fungal spores that have settled on the ground. Things that would not be inhaled by people on the ground will all float into the air, which will increase the probability of allergies. A friend of mine who works in the allergy department told me that every spring when the poplar hair is blowing, as long as there is a strong wind of level 5 or above, twice as many people come to report allergy reports the next day, all of which are caused by rhinitis and conjunctivitis caused by the hair blowing all over their faces.

When I usually do science popularization for the community, the most common question I get asked by the elderly is "Is spring cover and autumn freeze really useful?" In fact, there is no universal health formula. To put it bluntly, it still depends on the weather combination of the day. If the temperature slowly drops in autumn, the humidity is right, and the air quality is good, it is okay for you to exercise your body's resistance to the autumn freeze twice. But if not only the temperature drops, but there is also strong wind and smog that day, and you are still hanging out in single clothes, that is not called autumn freeze, it is called taking the initiative to kill someone.

Of course, there are still many things that are not clear about this issue. For example, under the same weather conditions, are sensitive people in the south more tolerant than those in the north? Will the trigger threshold be different at high altitudes? There are even studies saying that the intensity of ultraviolet rays can also affect it. When the ultraviolet rays are strong, they can kill some viruses in the air, and the risk of disease is low. However, these conclusions are not supported by a large enough sample size, and the academic community is still arguing.

For us ordinary people, there is no need to wait for the results of the academic dispute. When looking at the weather forecast, don’t just look at the temperature. Take a closer look at the humidity and air quality. Wear a mask to cool down, turn on a humidifier when dry, and open windows less often on hazy days. If you do these things in place, you can at least avoid most respiratory diseases from coming to your door. No matter how many supplements you take, it will be more effective.