Re-Infection after Explantation of Infected Hernia Mesh: Are the Same Micro-Organisms Involved?

Patients and Methods

Our method of identifying mesh explantation because of infection after hernia surgery has been described previously [1,4,7]. Briefly, all patients undergoing ventral/incisional, umbilical, and inguinal hernia repairs from the Veterans Affairs Surgical Quality Improvement Program (VASQIP) during 2008–2015 were included. Possible mesh explantation occurring between three days after surgery through five years were identified using Current Procedural Terminology (CPT) procedure codes and International Classification of Diseases (ICD)-9 and ICD-10 codes in either the inpatient or outpatient setting. These codes are not specific to hernia mesh explantation, therefore, all instances were manually reviewed by a trained surgeon. Patients with mesh explantation because of infection were followed through December 2020 for surgical site occurrences and re-repair of the same defect by performing manual chart review using the VA's integrated medical record system.

We then obtained data on cultured organisms from the mesh site at the time of index explantation and at any re-infection or subsequent explantation. Micro-organisms were classified as gram-positive, gram-negative, or others occurring as mixed or single. Micro-organism species were identified and matched across subsequent infections in the same patients. Approval to conduct this study was obtained by the VA Boston Health Care System Institutional Review Board.

Results

We identified 332 patients undergoing mesh explantation because of infection (64.8% ventral, 18.7% umbilical, 16.6% inguinal). Mean age was 60.3 years (standard deviation [SD], 9.7) and 93.9% were male. A culture was performed in 250 of 332 patients (75.3%) who underwent mesh explantation. No growth was reported in 66 patients (26.4%), compared with a single organism in 149 patients (59.6%) and multiple organisms in 33 patients (13.2%). Among 149 patients with a culture performed and single organism growth, 110 (73.8%) were gram-positive, and 39 (26.1%) were gram-negative (Fig. 1A). In 33 patients with multiple organisms, 50.4% were gram-positive, 45.3% were gram-negative, and 4.3% other.

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FIG. 1.

(A) Micro-organisms cultured after index mesh explantation. *Sixty-six cultures with no growth reported. (B) Micro-organisms cultured in re-infection after first subsequent hernia repair. *Two cultures with no growth reported. (C) Micro-organisms cultured in re-infection after second subsequent hernia repair. (D) Micro-organisms cultured in re-infection after third subsequent hernia repair.

A first subsequent repair for recurrent hernia was performed in 274 of 332 (82.5%) patients. Recurrent infection occurred in 58 of 274 (21.2%). Of these, 39 of 58 (65.5%) had a culture and no growth was reported in two (5.1%). A single organism was present in 27 (69.2%), of which 23 of 27 (85.2%) were gram-positive, four of 27 (14.8%) were gram-negative, and multiple organisms were reported in 10 of 39 (25.6%). Among 10 patients with multiple organisms, 55.2% were gram-positive, 38.2% were gram-negative, and 6.6% other (Fig. 1B).

Fifty patients underwent a second subsequent repair for second hernia recurrence. Among those, 12 of 50 (24%) had another hernia-related infection, of whom nine of 12 (75%) had a culture with eight of nine (88.9%) reported as single organisms and one of nine (11.1%) reported as multiple organisms. All eight patients with a single organism were gram-positive (Fig. 1C).

Eight patients had a third subsequent repair for third hernia recurrence. Two of eight (25%) had a new hernia-related infection, of which one (50%) had multiple organisms and one (50%) was a gram-positive single organism (Fig. 1D).

The species level of organisms is shown in Table 1. The same organism was cultured at reinfection in 23 of 59 (39%) cases. Gram-positive micro-organisms were the most prevalent in 20 of 23 (87%). Among the gram-positive micro-organisms, Staphylococcus aureus was the most common pathogen and was cultured in 18 of 20 (90%) cases, of which 14 of 18 (77.8%) were methicillin-susceptible Staphylococcus aureus (MSSA) and four of 18 (22.2%) were methicillin-resistant Staphylococcus aureus (MSRA). Three of 23 (13%) gram-negative organisms were the same at both re-infection and index explantation consisting of Escherichia coli in two of three (66.7%), and Pseudomonas aeruginosa in one of three (33.3%; Table 1).

Discussion

This is the first study to our knowledge to evaluate causative organisms cultured at the time of initial explantation for infection of hernia mesh and the role of these organisms in infections after multiple subsequent repairs.

We found that each subsequent hernia repair after index mesh explantation because of infection carries a risk of developing re-infection of approximately 25%. In an abdomen that has sustained multiple incisions and dissections, it is more likely for the tissues to have altered vascularity and impaired wound healing [5,6]. Prior work has shown that a history of prior surgery is associated with increased risk of surgical site infection (SSI) and presence of bacteria that increase the risk of reinfection [6].

A single gram-positive micro-organism was the most common organism cultured, comprising more than 75% of cases at index explantation and subsequent reinfections. Staphylococcus aureus was the most common organism among the gram-positive micro-organisms. This supports previous recommendations [8] that patients undergoing hernia surgery should be given prophylactic antibiotic agents active against gram-positive micro-organisms and specifically Staphylococcus aureus.

The same organism was cultured after each subsequent hernia repair infection in more than 45% of the cases (Table 1). Staphylococcus aureus was again the most common organism cultured. It is unknown whether in these patients the re-operation occurred too soon in a potentially contaminated field or if the organism remains dormant or inactive in the patient's tissues. It is therefore essential to allow all incisions to heal completely prior to undertaking another repair and to give appropriate prophylactic antibiotic agents targeting sensitivity of previously cultured micro-organisms.

Conclusions

Identification of organisms at the time of prosthetic infection is helpful not only in treating the initial infection but crucial in the predicting microbiology and providing appropriate empirical therapy for subsequent repairs.

Same-organism re-infection should not be underestimated, particularly when Staphylococcus aureus is isolated, and prophylaxis against gram-positive organisms should be considered. Because most of these gram-positive organisms were Staphylococci, consideration should be given to the pre-operative assessment of Staphylococcus aureus colonization and decolonization of these patients if positive.