Is disease screening considered secondary prevention?

In most public health practice scenarios, disease screening is indeed the core implementation measure of secondary prevention. However, in a few subdivided scenarios, there are still some disputes between the academic community and front-line public health personnel.

The three-level prevention often mentioned in the field of public health is like building three flood embankments for health: the first-level prevention is to plant trees and build dams upstream to reduce the possibility of flooding from the root cause, such as vaccination, salt control and oil control to prevent high blood pressure. The goal is to "not get sick."”； Secondary prevention involves installing water level monitors in the middle reaches and digging temporary flood discharge channels. The floodwaters have just exceeded the warning level and have not yet washed down. The core is the "three early" measures of early detection, early diagnosis, and early treatment. The goal is "not to develop into a serious disease."” ； The third level of prevention means that the downstream areas are already flooded, so disaster relief and disaster reduction should be carried out quickly to prevent disability and improve the quality of life.

The screening we usually come into contact with the most is basically stuck at the node of secondary prevention. For example, I used to organize two cancer screenings in the community. The 42-year-old Aunt Zhang in the community usually did not feel uncomfortable at all. The screening revealed high-grade precancerous lesions on the cervix, and a small conization was performed in the outpatient clinic. There are also low-dose spiral CT screening for lung cancer and fasting blood glucose screening for diabetes arranged for people over 60 years old. They are both targeted at healthy people without symptoms and look for early-stage lesions that have occurred but have not yet shown symptoms. They are completely in line with the core logic of secondary prevention.

However, when I talked about this topic with Lao Zhou, who is responsible for chronic disease prevention and control at the CDC, he also mentioned that there are indeed different views now. For example, Helicobacter pylori screening is often recommended now. This bacterium is a first-level carcinogen of gastric cancer. Many people will be infected for more than ten years before it progresses to cancer. Direct eradication treatment after detection is equivalent to blocking the occurrence of gastric cancer from the cause level, and does not wait for the gastric mucosa to become cancerous. Many scholars believe that this kind of screening for risk factors is more of a supporting measure for primary prevention. There is also neonatal phenylketonuria screening, where blood is collected and screened just after the child is born. As long as a positive result is found, the child is immediately fed with special formula milk. The child will not show symptoms of mental retardation or developmental abnormalities at all, which is equivalent to stopping the disease before it occurs. Some people think that this kind of screening should be classified as primary prevention.

In fact, the essence of this controversy is that many screening projects do not only focus on a single indicator, but often cover disease risk factors and early lesions at the same time. Just like the multi-functional alarm installed in your home, it will not only remind you to prevent fires when smoke is coming out, but also detect gas leaks and remind you to open the window. It is difficult for you to strictly classify it as a fire alarm or a gas alarm. The functions overlap.

For us ordinary people, there is no need to get entangled in the minutiae of this academic definition. As long as it is age-appropriate screening recommended by regular medical institutions and disease control departments, and exclusive screening for high-risk groups, you can do it with confidence. The cost of early detection is much lower than that of treating late-stage disease, and the suffering is not at the same level.