Our data showed that the average body temperature of the Gram-negative group was higher compared with the Gram-positive group, and the number of patients with urinary tract infection in the Gram-negative group was significantly greater compared with the Gram-positive group (P < 0.05). In the univariate analysis, patients with body temperature ≥ 38℃ and antibiotic treatment time < 6 weeks showed recurrent infection. In the multivariate logistic analysis, antibiotic treatment time < 6 weeks was an independent risk factor for recurrent infection.
Pyogenic spondylitis is mainly caused by the spread of bacteria through the blood source. The arterial route is more common than the venous route. The spinal blood supply is abundant, and it is more susceptible to bacterial transmission and infection . In the Gram-negative group, E. coli accounted for the highest proportion, followed by Klebsiella pneumoniae. Among the 62 cases of Gram-negative bacterial infection reported by Seung-Ji Kang et al. , Escherichia coli accounts for the highest proportion, followed by Pseudomonas aeruginosa. In our Gram-positive group, Staphylococcus aureus accounted for the highest proportion, followed by coagulase-negative Staphylococcus. It is widely reported that Staphylococcus aureus is the most common strain [1, 5, 10]. Pyogenic spondylitis usually affects the elderly [11, 12], and the most common site is the lumbar spine, followed by the thoracic spine and cervical spine . Usually, pyogenic spondylitis is more frequently detected in males compared with females . The most common symptom is focal spinal pain, and other symptoms include fever and neurological symptoms . The above-mentioned characteristics were also well reflected in this research.
The average age of the Gram-negative group was higher compared with the Gram-positive group, while the difference was not statistically significant (P > 0.05), which was similar to the data reported by Ching-Yu Lee et al. . The admission body temperature of the Gram-negative group was significantly higher compared with the Gram-positive group (P < 0.05). Because the two pathogenic mechanisms are different, and Gram-negative bacteria rely on endotoxin to cause disease. The toxic component is mainly lipid A, which is not easy to be dissolved in blood vessels and surrounding tissues. However, it can cause fever, microcirculation disorders, endotoxin shock and disseminated intravascular coagulation in blood vessels. Therefore, the body temperature of the Gram-negative group was higher compared with the Gram-positive group. Gram-positive bacteria can produce special pathogenic factors, such as protein A and coagulase, which can invade tissues or blood vessels, causing necrosis and dissolution of surrounding tissues. Subsequently, a large number of neutrophils infiltrate, forming a cavity filled with pus. In the present study, there was no statistically significant difference in spinal abscess between the two groups.
Our research showed that there were significantly more patients with urinary tract infection in the Gram-negative group compared with the Gram-positive group (P < 0.05). KH Park and other studies have shown that the main source of infection of Gram-negative pyogenic spondylitis is urinary tract infection . Ching-Yu Lee et al. have also shown that Gram-negative pyogenic spondylitis is more complicated with a history of urinary tract infection . Diabetes is the most common underlying disease, although there are reports that pyogenic spondylitis caused by Gram-negative bacteria is related to diabetes . However, our study and Dong Youn Kim et al.  did not find any connection between these two factors.
There is no clinical guideline for conservative treatment and surgical treatment . When conservative treatment is effective, and there is no spinal instability, spinal nerve compression damage, or symptoms that are progressively worsening, conservative treatment, such as antibiotics, can be used . In the selection of antibiotics, sensitive antibiotics should be selected for treatment based on the results of Gram staining and drug sensitivity experiments. There is no uniform conclusion on the duration of antibiotic treatment. The American Academy of Infectious Diseases believes that antibiotic treatment should last at least 6 weeks . A published randomized controlled trial shows that 6 weeks of antibiotic treatment for pyogenic spondylitis is as effective as 12 weeks , while this study has only included patients with positive microbial cultures. Research by Park KH and others has concluded that antibiotic therapy should be continued for at least 8 weeks for patients with a high risk of recurrence . Generally speaking, the duration of antibiotic treatment should be no less than 6 weeks . Most of the patients (66/76) in this study were treated with antibiotics for more than 6 weeks. Some studies have shown that treatment of less than 6 weeks is associated with an increased recurrence rate . Similarly, our research revealed that the duration of antibiotic treatment < 6 weeks was an independent risk factor for recurrence.
When conservative treatment is ineffective, and there are spinal instability, impaired spinal nerve compression and progressive symptoms, surgery in combination with antibiotic therapy can be used [11, 21, 22]. E Pola et al. have reported a minimally invasive surgery in combination with antibiotic treatment regimen, and good clinical results have been achieved .