Secondary infections are caused by patients who, after being infected with a pathogenic microorganism or suffering from a certain disease, are infected with new pathogens or the original latent pathogens in the body are resurrected due to various reasons, such as irrational treatment, low immunity, etc. The emergence of infections is due to the fact that patients are infected with a pathogenic microorganism or suffering from a certain disease. There are many reasons leading to secondary infection, the most common is the long-term improper use of antibiotics, such as pneumonia patients with intravenous infusion of antibiotics for too long, or choose too strong antibiotic treatment, may lead to intestinal flora imbalance, which leads to non-pathogenic latent bacteria in the gastrointestinal tract to cause disease, the patient may have abdominal pain, diarrhea, nausea, vomiting and other symptoms of the gastrointestinal tract. Causing secondary infection can also be seen in the original bacterial infection, after treatment, and then re-infected with other types of pathogens, such as fungal infections, especially in the inappropriate use of antibiotics or prolonged use of antibiotics, easy to induce fungal infections. Secondary infections are more common in patients with underlying medical conditions, such as those with chronic kidney disease and diabetes. Secondary infections can also be seen in secondary peritonitis, which is usually an acute inflammatory condition secondary to the entry of large amounts of digestive fluids and bacteria into the peritoneal cavity caused by inflammation, rupture, perforation, abdominal trauma, or surgery of the organs in the abdominal cavity. Secondary infections should be treated promptly under the guidance of a physician to avoid delays.