The three of them exchanged a look.

Another classmate said, "Isn’t this that patient?"

Zhaxi’s heartbeat sped up. "But how does a Clostridium difficile infection cause an aneurysm?"

Zhaxi kept scrolling down. "The literature says that C. difficile infects the intestinal tract and destroys the intestinal mucosal barrier, allowing bacteria to enter the bloodstream. Once in the blood, if there’s damage to the heart valves, it causes endocarditis; if there’s damage to the vessel wall, it causes an infective aneurysm."

He paused and pointed at the screen. "Look at this figure—the formation process of an infective aneurysm. Bacteria adhere to the blood vessels, causing local inflammation, the vessel wall gets destroyed, slowly bulges out, and forms an aneurysm. This process can go on for months, and it’s only discovered when it ruptures."

A thought suddenly flashed through Zhaxi’s mind.

That patient had started having fever, diarrhea, and weight loss half a year ago. Half a year is enough time for an infective aneurysm to form.

He took out his notebook and wrote this idea down.

On Wednesday morning, Yang Ping went to the Overseas Chinese Building again. Zhaxi followed behind him, carrying all the papers he’d read the night before in his mind. He wanted to speak up several times, but swallowed it back each time.

In the ward, the patient looked a little better than the day before yesterday, but was still weak. The woman was sitting by the bed. When she saw Yang Ping come in, she stood up, and there was more expectation in her expression.

Yang Ping asked a few questions about the illness and then performed another neurologic exam before saying, "The recovery is okay. The hemorrhage is slowly being absorbed."

The woman let out a breath of relief, but then frowned again. "Professor Yang, what about the aneurysm? That thing is still there, and we just can’t feel at ease, but we also don’t want him to have surgery, so we’re really torn. Please help us make a decision. We’ll follow your advice."

Yang Ping nodded and said, "I understand, but given the current situation, the surgical risk really is high. I’d like to review his medical history again and see if there’s any other possible approach."

The woman was taken aback. "Another approach?"

Yang Ping said, "Some aneurysms don’t necessarily have to be treated with surgery. If we can find the cause, there may be other ways to manage it." He paused. "Let me ask a bit more about his medical history. Over these six months, besides diarrhea and fever, did he have any other discomfort?"

The woman thought for a moment and said, "Joint pain. There was a period when his knees and wrists hurt. We thought it was some autoimmune rheumatic disease, but the tests didn’t show that."

A faint light flashed in Yang Ping’s eyes. "Did he take any medications? Antibiotics, anti-inflammatory drugs, that sort of thing?"

The woman said, "Yes. When he had the fever, the community hospital prescribed a cephalosporin, and he took it for seven or eight days. Later he took other stuff too, I don’t remember exactly, but he definitely used antibiotics several times."

Yang Ping nodded and asked again, "When was his diarrhea at its worst?"

The woman recalled, "Right around the time he was on those meds. I thought the drugs upset his stomach, but the doctor said no, said it was irritable bowel syndrome and told him not to stress."

After he finished asking, Yang Ping said, "Don’t worry just yet. I’ll go back and think it over, and see if there’s any better option."

Once they were out of the ward, Zhaxi finally couldn’t hold back. "Professor Yang, are you suspecting Clostridium difficile?"

Yang Ping halted, turned to look at him, a hint of surprise in his eyes, and smiled. "You know about C. difficile?"

Zhaxi nodded and recounted the papers he’d read the previous night. When he finished, he watched Yang Ping nervously, like an elementary school student waiting for the teacher to grade his homework.

When Yang Ping finished listening, he laughed.

"Not bad. You know to look up the literature now," he said. "But you missed a key point."

Zhaxi froze. "What is it?"

Yang Ping said, "For a C. difficile infection, what do we rely on for diagnosis?"

Zhaxi thought for a moment. "On...stool culture?"

"Exactly," Yang Ping said. "But has this patient had diarrhea during these days in the hospital?"

Zhaxi was taken aback. He remembered the family saying he hadn’t really had diarrhea during the hospitalization because he wasn’t eating.

"If he’s not having diarrhea now and we can’t get a stool specimen, how do we test?" Yang Ping asked.

Zhaxi opened his mouth but couldn’t come up with an answer.

Yang Ping patted him on the shoulder. "Your thinking is on the right track, but clinical work isn’t a guessing game. You need evidence before you can make a diagnosis. Right now the evidence chain is missing a link."

He finished speaking and walked toward the elevator.

Zhaxi stood where he was, stunned for several seconds. The evidence chain was missing a link—missing which link?

He caught up, wanting to ask, but Yang Ping had already stepped into the elevator.