"People infected with COVID-19 have long-term abnormal lung function"? A secret to debunk this rumor

If you interpret the paper carefully, you will find that the relevant research that "1/4 of people infected with the new coronavirus have abnormal lung function one year later" actually gives an optimistic conclusion.

Written by Li Changqing (Doctor of Medicine, practicing physician in the United States)

Chinese-American epidemiologist Eric Feigl-Ding recently posted a message on social media saying that one-quarter of people infected with the new coronavirus still have abnormal lung function one year later.

As an epidemiologist who mainly studies obesity, Ding Liang has always had a strong sense of anxiety about COVID-19, a respiratory disease, and his related analysis and comments have therefore received a lot of attention. Although the topic of COVID-19 is becoming less and less popular nowadays, a considerable number of people still express concern and even panic about such bad news.

So is it true, as Ding Liang said, that studies have shown that 1/4 of COVID-19 patients still have abnormal lung function one year later? You only need to look at the paper on which it is based to know. The study was conducted by Dutch doctors. The abstract of the paper shows that they tested the lung function of patients diagnosed with COVID-19 from May 2020 to early 2021, and then repeated the test 6 months and 12 months after infection. The results showed that 25% of the subjects still had abnormal lung function one year later, and the proportions of patients with mild, moderate and severe symptoms were 11%, 22% and 48% respectively.

However, this is just an abstract. If you read the full text, you will know that the so-called 1/4 does not refer to the general population. It is impossible for any study to test all infected people, only some patients. Whether this part of the patients can represent the entire population depends on whether they are randomly selected from the population and whether the sampled population is large enough. This study included a total of 300 subjects, which is not large for a widely spread disease like the new coronavirus; more importantly, these people were not randomly selected, but selectively included. Nearly half of this population are hospitalized patients (48%), which is obviously much higher than the hospitalization rate of infected people in the general population, so their indicators cannot represent the general population.

Looking at the detailed values ​​of the study, the abnormal lung function index they reported is DLCO (diffusing capacity for carbon monoxide), which represents the ability of the gas in the alveoli to diffuse into the blood. If this data is relatively low, it means that the diffusion function of the lungs is impaired. If it is above 75% of the predicted value, it is considered normal. From the average values ​​they reported, the DLCO of patients with mild and moderate symptoms is above 75% (the average for mild patients is greater than 90%, and the average for moderate symptoms is greater than 80%). Even for severe patients, the average value reached more than 75% after one year.

In general, this should be a relatively optimistic report, and the conclusion is that most patients did not have obvious abnormal lung function when infected, and even severe patients had considerable recovery of lung function one year later. However, the author insisted on choosing such a shocking title, and it was discovered by "experts" who were hungry for negative news about the new coronavirus.

There are many headline-grabbing reports like this. As long as there are such experts and media willing to act as the second-hand setters of "problem research", they will continue to mislead the public. Not everyone (including media people) is capable of interpreting such reports. Here I will use the COVID-19 as an example to provide you with a simple interpretation secret (also a principle), which is to see if these reports are compared with other common respiratory viral infections, such as viral upper respiratory tract infections or influenza. If there is no comparison, it can be ignored.

I have good reasons to say this. Although the COVID-19 pandemic has not been officially declared over, many parts of the world, including China, have already taken measures to basically end it, mainly in the form of no longer routinely testing ordinary hospitalized and emergency patients for COVID-19, and the cancellation of cross-border testing and quarantine requirements. The most important basis for this is that the infection rate, hospitalization rate, and mortality rate of COVID-19 have been greatly reduced, and now the mortality rates of influenza and COVID-19 are basically the same for the entire population.

In other words, the characteristics of COVID-19 that are similar to other infectious diseases such as seasonal influenza should no longer be treated specially. The same should be done for the long-term COVID-19 and COVID-19 sequelae exaggerated by panic makers.

As a new infectious disease, COVID-19 has received special attention from the public and the media, which has led to the amplification of many COVID-related symptoms and complications. For example, COVID-related loss of taste and smell, myocarditis, encephalitis complications, etc., are not unique to COVID-19, but also occur in many respiratory infectious diseases, including influenza. Since we can take flu-related symptoms and complications in stride, we should not panic about COVID-19.

The same is true for the so-called long COVID. A certain proportion of patients with any acute respiratory viral infection have long-term symptoms, some of which can last for weeks, years or even lifelong. These symptoms are very similar to those of long COVID, such as fatigue, muscle aches, difficulty breathing, and inattention. According to reports, the proportion of long-term symptoms in COVID patients is higher than that in influenza patients, at approximately 42% and 30% respectively. Both of these proportions seem a bit too high, probably because the definition of long-term symptoms is too broad. According to actual clinical observations, long-term symptoms after both long COVID and influenza are not as common as some reports have portrayed.

In the post-epidemic era, if someone only reports on the sequelae of COVID-19 without comparing it with other common respiratory infectious diseases, then such reports can be considered of little value. If a report like this one in the Netherlands deliberately gives a shocking title, then it can be characterized as sensationalism.

This article is supported by the Science Popularization China Starry Sky Project

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

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