respiratory disease meteorological conditions

Sudden temperature changes with a 24-hour temperature difference of ≥8°C, polluted days with an average daily concentration of PM2.5 higher than 75 μg/m³, extremely dry days with a relative humidity lower than 30% or high humidity days higher than 90%, and calm windless weather with temperature inversion are the four core high-risk meteorological conditions that induce respiratory diseases.； If multiple conditions are superimposed, the number of respiratory-related outpatient and emergency visits in medical institutions will increase by 30% to 70% compared with normal times. The risk of illness for the elderly, children, and patients with basic respiratory diseases is 3 to 5 times higher than that of healthy people.

When I was rotating in the respiratory department of a tertiary hospital last fall and winter, I happened to encounter a typical high-risk weather: the highest daytime temperature was still 16°C the first day, a cold wave passed through at night, and the highest temperature dropped directly to 3°C the next day. At the same time, there was a steady temperature inversion for three consecutive days, and the PM2.5 concentration exceeded 120 μg/m³. The number of outpatient clinics doubled that week. Among the 27 patients received in the morning, 11 were children with acute asthma attacks, 8 were elderly people with acute exacerbation of chronic bronchitis, and many young people who were usually in good health were found to have viral pneumonia if their high fever persisted.

Interestingly, the academic community has been arguing about the impact of temperature for a while. In the early years, there was a school of thought that low temperature itself was the main cause of respiratory diseases. After all, the number of doctor visits in winter was much higher than in summer every year. But later, a team from the Harbin Center for Disease Control and Prevention tracked local winter clinic data for three years and found that the number of doctor visits was very stable during the extremely cold days lasting minus 20 degrees Celsius. The real peak of doctor visits is always the first day of cooling and the first two days of sudden warming in spring - the latter also adds a buff of soaring pollen concentration, and the number of doctor visits for allergic rhinitis can directly triple. To put it bluntly, the human respiratory tract has a high tolerance for "constant extreme temperatures". What it fears is the stimulation of "switching hot and cold". If the mucous membrane fails to keep up with the adjustment rhythm, viruses and bacteria will take advantage of it.

Let’s talk about the humidity that everyone easily ignores. After sleeping with the heating on all night in winter, your throat will feel as dry as if you have swallowed sandpaper. This is actually a typical symptom of too low humidity: when the relative humidity is lower than 30%, the ciliary swing speed on the surface of the respiratory mucosa will drop to 1/3 of the normal level, and the dust and viruses stuck on it cannot be discharged at all, and the probability of infection will naturally increase significantly. But the wetter is not always better. Friends in the south must be well aware of the power of returning to the south. When the relative humidity exceeds 90%, mold spores and dust mite secretions can float in the air. I once treated an old COPD patient from Zhuhai. He said that as soon as he returned to the south, he had to run to his children's house in the north. He didn't need to take any medicine, and his symptoms of coughing and asthma were reduced by half in the same day, which is more effective than any other treatment.

As for the impact of pollutants and temperature inversion, there are now different research conclusions. One group believes that the impact of PM2.5 is greater than the temperature. These small particles with a diameter of less than 2.5 microns can directly penetrate the respiratory tract barrier and penetrate into the alveoli. Not only can they induce acute infections, but long-term exposure can also increase the risk of interstitial pneumonia and lung cancer. However, some studies have pointed out that as long as there is no superposition of sudden temperature changes, simple mild pollution (PM2.5 concentration 75~115 μg/m³) has a very limited impact on healthy adults. Only the elderly, children, and patients with underlying diseases need to focus on protection and do not need to be overly anxious. Just think of a temperature inversion day as putting an airtight lid on the city. Car exhaust, dust from construction sites, and even smoke from roadside barbecues cannot escape. They all pile up in the air near the ground. If they stay there for a long time, problems will easily arise.

In the past two years, our department has established a joint health warning mechanism with the local meteorological bureau. Every time the above-mentioned high-risk weather conditions are predicted to occur, a reminder is sent to patients with asthma, COPD, and allergic rhinitis who have been registered in the community in advance, telling them not to go out for exercise too early. Try to wear N95 outside the door, and use a humidifier or dehumidifier at home to control the humidity between 40% and 60%. With such a simple measure, the hospitalization rate for respiratory diseases in our jurisdiction dropped by 15% last winter, and the effect was much better than we expected.

In fact, there are still many things that have not been thoroughly studied about the relationship between respiratory diseases and meteorological conditions. For example, the tolerance levels of people in different regions vary greatly. People from the Northeast can go out for a walk at minus 20 degrees Celsius for half an hour without any problems, while people from the South may catch a cold on rainy days at around zero degrees Celsius. There is no universal warning value. To put it bluntly, weather conditions are just external triggers. Wearing a mask when going out, adding or removing clothes in time according to the temperature, and exercising regularly to improve immunity are more effective than any weather warning.