Response to Letter to the Editor for: Comparison of Surgical Site Infection After Instrumented Spine Surgery in Patients With High Risk of Infection According to Different Antibiotic Prophylaxis Protocols: A Cohort Study of 132 Patients With a Minimum Follow-Up of 1 Year

We would like to thank the editors for the opportunity to clarify some important points of our work proposed in the Letter to the Editor regarding the article “Comparison of Surgical Site Infection After Instrumented Spine Surgery in Patients With High Risk of Infection According to Different Antibiotic Prophylaxis Protocols: A Cohort Study of 132 Patients With a Minimum Follow-Up of 1 year.”

First, maintaining an adequate concentration of antibiotics in the blood is essential to avoid surgical site infections (SSI). The dose of antibiotics is repeated in the case of prolonged surgery or heavy blood loss. Currently, we do not monitor antibiotic serum concentration during surgery in our clinical practice. This will be an interesting option to consider in future studies. However, as the main goal of the work was to compare the efficacy and safety of different antibiotic protocols, the exact serum concentration was not the scope of our study.

Second, different etiologies have been described as responsible for SSIs: hematogenous dissemination, contamination of the surgical site during the intervention, or due to a pre-existing microbiota in the patient. The authors consider that it might consist of a multifactorial mechanism, not just due to one factor but a combination of the factors described above. ¹ Long et al ² pointed out that endogenous wound contamination with enteric flora may be a common mechanism of infection in lumbosacral fusion. However, at the cervical level, the pathogens would be more related to the cutaneous flora. Other possible endogenous causes are nasal colonization or urethral colonization.^3,4 Krizek and Robson, ⁵ suggested that a large part of the infections occur due to contamination of the surgical site during the intervention.

Third, as stated by Sarfani et al, ⁶ many patients who claim to be allergic to penicillin are not actually allergic. To avoid this frequent misdiagnosis, our protocol includes allergology referrals to all patients reporting allergies related to antibiotics. This way, in our series, on a total of 132 patients, only 2 needed vancomycin. We believe that this small number does not affect the results. On the other hand, the fact that the use of vancomycin as monotherapy as prophylaxis increases SSI is controversial. Tan et al ⁷ did not find any association between the use of vancomycin and the risk of developing SSI (although this study was carried out in patients who underwent total joint arthroplasty and not spinal surgery). However, the use of vancomycin is associated with a higher risk of developing gram-negative infections. These findings support the hypothesis of our work since second-generation cephalosporins have a certain effect against gram-negative bacteria, which vancomycin does not. Therefore, active prophylaxis against gram-positive and gram-negative bacteria reduces SSI rates.