Little Wang came in again, a little embarrassed, and said, “Doctor, I still want to check my blood.” I remembered that he had come in about a dozen times, every week or two for an HIV check, and it had been a little over half a year by my reckoning. Each time Little Wang patiently stood in line, asking only for a blood test and occasionally asking questions about how long the window period for HIV is, how long the incubation period is, and so on. Xiao Wang had unclean sex after a drunken night half a year ago, and when he went home, he was very regretful and blamed himself, worrying that he had been infected with AIDS, bathing repeatedly and having a sleepless night. The next day, he went to the hospital to do a comprehensive physical examination, physical examination and laboratory results of all indicators are normal. He consulted a lot of information about AIDS on the Internet, worrying that in the “window period” can not be found, so he went to the hospital every week to check, so far, has been in a number of hospitals more than 20 times, or do not rest assured. In the past six months, she had to rely on sleeping pills to maintain her sleep, her appetite dropped significantly, and she lost 3kg of body weight; she had no fever, diarrhea, or enlarged lymph nodes, etc. Even though the doctor repeatedly explained to her that she did not have AIDS, she always wanted to go to the hospital for a final checkup to confirm her condition, and she was unable to control herself. Every time she saw public service announcements about AIDS on TV, wrote about AIDS on the Internet, or heard someone mention AIDS, she was very nervous and had to go to the hospital the next day for a checkup. I woke up in the middle of the night and often thought nonsense, and even imagined how to face my parents and colleagues and how to arrange for the aftermath after I had suffered from AIDS. Because of the long-term sleep is not good, mood irritability, although can barely cope with the daily work, but the work efficiency is reduced, made a few mistakes, they are more and more nervous. Interaction with coworkers has also been reduced, and after work, he locks himself at home to consult AIDS-related information, some of which has been repeatedly read many times, but he can not control his emotions and feels very painful. I also advised him that it has been almost half a year, the window period has passed, negative means no more, this matter is over, do not come back. However, he promised to come back every time, but he still came to the blood test on time. This time, Wang looked very haggard, “, I know it will be six months soon, but I still worry that I will be one of the very few exceptions? What if I am?” From a clinician’s point of view, I could basically rule out the possibility that Xiao Wang was infected with HIV, but then I had to play the role of a counselor. I asked Wang what information he had read and how much he knew about AIDS. I didn’t expect him to pull out a thick stack of materials from his bag, many of which were professional medical literature. I turned out one of the articles from August 31, 2013, which mentioned that the HIV infection rate among clandestine prostitutes is 0.3%, which means that out of 1,000 clandestine prostitutes, there are three infected people. I turned to the dermatology textbook again, which referred to the chances of transmitting HIV from a female to a male by giving him one unprotected sexual encounter as less than 0.1%. I asked King to do a multiplication, 0.3% x 0.1% = 3 x 10-6, which meant that his chances of contracting AIDS were estimated to be only three in a million. “The chances are small, but I’m still a little worried, what if I’m one of those rare exceptions?” Little Wang insisted. I said, “Okay, then let’s look together again at how likely it is that you are the exception, how long has it been since that incident?” Little King: “Six months” I asked him, “How many times have you been tested for HIV?” Without thinking, Xiao Wang replied, “24 times.” Looks like he’s been counting. I said, “Okay, you know that the window period for AIDS is 6 weeks-3 months, and the test we are using now is 99% accurate. Let’s do the math on a weekly test, and since week 6, you’ve had about 18 tests, each of which has been negative. So, let’s do a multiplication again, at an error rate of 1%, 14 times in a row, 1% x 1% …… all the way by 14 1%, what is the result? ” Xiao Wang was silent for a minute and said, “The checking error rate is basically zero.” I continued, then if according to the window period is 3 months, 12 tests are negative, what are the chances of checking error? Xiao Wang: “Multiplying 12 1%, the chance of a test error is also zero.” I noticed that Wang said that the chance of a test being wrong was “basically zero”, but now he said that the chance of a test being wrong was “also zero”. This was a welcome change, and he was gradually accepting it. At this point, there were dozens of patients waiting outside the door, and there was no way I could help him further, either in terms of time or professional ability. I said, “Xiao Wang, you also believe that you are not infected, right? As far as I can observe your mental state is also completely normal, you just encountered some troubles for a while, I suggest you go to a professional psychiatrist to have a look, they will help you recover completely.” Xiao Wang let out a long breath and said, “Good!” It was obvious that he had already relieved himself a bit. Of course, Xiao Wang’s psychological problems will not be solved by this small conversation, there may be more complicated causes, and more professional psychological counseling is also needed. Physical and mental illnesses are often intertwined, it is difficult to distinguish between them. People in the industry often say that the dermatologist’s eyes are worth a lot of money, and often do not need to rely on too many laboratory tests, “look” a glance can be diagnosed. However, if your eyes are only on the rash, and you don’t pay attention to the patient’s whole body, including the psychological condition, you are doomed to fail to solve most of the problems.