Disease screening and census belong to several levels of prevention

Disease screening and census are typical secondary prevention in the mainstream public health tertiary prevention system.

Many people may not be so familiar with the concept of tertiary prevention. To put it simply, it is the three lines of defense drawn for disease prevention and control in the public health field. The first step is primary prevention, also called etiological prevention, which means taking action in advance before being exposed to the causative factors. For example, taking the HPV vaccine to prevent cervical cancer, controlling smoking to prevent lung cancer, adding iodine to salt to prevent goiter, and teaching everyone to wear masks correctly to prevent COVID-19 during the epidemic, all of which reduce the probability of getting the disease from the root. The core goal is to "not get sick."

The core of secondary prevention is the often-heard "three early stages" - early detection, early diagnosis, and early treatment. It is aimed at the "pre-clinical" stage when the disease has quietly taken root in the body but has not yet shown obvious clinical symptoms. At this time, the cost of intervention is extremely low and the effect is particularly good when the problem is identified. This is exactly what screening and census are for: whether it is free fasting blood glucose testing for the elderly in communities every year, low-dose lung cancer CT, or two-cancer screening for women of childbearing age, scoliosis screening for primary and secondary school students, and occupational health physical examination chest X-rays for factory dust workers, their essence is to identify potential patients among asymptomatic people, completely fulfilling the core positioning of secondary prevention.

When I helped with the rural cancer screening project at the district and county CDC two years ago, I also talked with many public health colleagues about the boundary issue of this classification. Now there are indeed a small number of different voices in the industry. For example, when we went to a remote village for cervical cancer screening, we not only conducted TCT sampling, but also set up mobile HPV vaccine vaccination sites to make on-site appointments for women of appropriate age who had never been vaccinated. At the same time, we also held small health classes to teach the prevention of gynecological diseases. In this binding model of "screening + pre-cause intervention", some scholars have proposed that the classification of secondary prevention should not be applied directly, and that combined primary and secondary intervention is more appropriate. However, in this special situation, which belongs to a small number of customized projects, the general consensus among academic circles is to classify routine and simple screening and census as secondary prevention.

Let me tell you something that particularly impressed me. Last year, our district conducted free bowel cancer screening for the elderly. There was a 72-year-old Uncle Zhang who refused to come at first. He said that he had regular bowel movements every day. This screening was a waste of public resources. He was half-hearted by the community family doctor. The genius reluctantly took a stool sample, which turned out to be positive for occult blood. A further colonoscopy revealed that it was very early-stage adenocarcinoma. The patient was immediately removed under the microscope without even using chemotherapy. Now the old man is in very good health. Whenever he meets people, he says that it was thanks to the doctor who urged him to do the screening. If you think about it, if he really delayed going to the hospital until he had symptoms of blood in the stool and abdominal pain, he would most likely be in the middle to late stage. Not to mention the hundreds of thousands of treatment costs, the person would suffer a lot, and the prognosis might not be good. This is the most real value of secondary prevention - spending tens of dollars in screening costs can save hundreds of thousands in treatment fees, and even save a life.

In fact, the tangled classification is not essentially about academic word-picking. It is mainly to facilitate public health practitioners to find the right direction when designing projects, and to explain the principle of "screening even if you are not sick" to the common people when doing science popularization. After all, for most chronic diseases and malignant tumors, it is too late to go to the hospital until you have obvious symptoms. Maintaining the line of defense of screening is better than anything else.