In our study, CA-IAI patients had a higher 28-day mortality rate than those with HA-IAI. However, at 90 days, the mortality rates were similar in both groups. Based on our knowledge, few studies actually compare outcomes for patients with CA-IAI and HA-IAI. Van Ruler et al. noted mortality rates of 13% for patients with CA-IAI and 30% for those with HA-IAI, including patients with an APACHE II score above 10 (7). Montravers et al. found a mortality rate of 4% for patients with CA-IAI and 12% for patients with hospital-acquired, non-postoperative peritonitis in a mixed population of ICU and non-ICU patients (15). Inui et al. observed a mortality rate of 3.8% for patients with CA-IAI and 8.4% for HA-IAI patients. This study included IAI with or without surgical treatment (16). In a multicentre study, no significant difference in mortality rate was reported in patients with CA-IAI and HA-IAI (5). These findings probably reflect differences in the inclusion criteria, endpoint definitions and the type of IAI.
We can only assume the reason for the difference in the 28-day mortality rate. Our two groups are similar in terms of severity criteria and APACHE II score. However, there is no delay between the onset of symptoms, initiation of antibiotic treatment and surgical management, which can be a major confounding bias. No peritoneal sample was collected for a large number of CA-IAI patients. Therefore we did not know whether antimicrobial treatment was adequate. Furthermore, in-patients were more likely to receive broad-spectrum antibiotics. Some patients from the HA-IAI group were already in the ICU when peritonitis developed, and therefore returned to the ICU after surgical management regardless of the severity criteria. These differences explain why death occurred earlier in the CA-IAI group than in the HA-IAI group. However, it should be noted that the mortality rate was similar at 90 days, which suggests the weak effect of early interventions.
A medical history of arterial occlusive disease, platelet count below 50000/mm3, creatinine serum levels greater than 150 µmol/l, and a high APACHE II score were also associated with a worse outcome. A BMI of over 23 was associated with a better outcome. Thrombocytopenia had already been described as a mortality-related factor in IAI, and acute kidney injury in critically ill patients and sepsis in particular (17,18). A meta-analysis studying overweight, obesity and sepsis reported an association with a better outcome (19). To the best of our knowledge, arterial occlusive disease has not been previously described as a mortality-related factor, but its association with coronary disease is well known, which could explain our findings (20).
Other outcomes, as defined by our study, have generally been poorly reported in previous studies, except for reoperation. This last endpoint is generally higher in HA-IAI patients (9,16). As in other studies, we report longer ICU and hospital stays for HA-IAI patients compared to those with CA-IAI (16,21).
The bacteriological findings were consistent with the literature, except for the rate of anaerobic bacteria (5,22). This may be attributed to poor quality of sampling, conditioning or logistics of the peritoneal sample. Our institution has taken measures to improve this. Empirical antibiotic therapy was appropriate in 72.5% of the CA-IAI group and 82.2% of the HA-IAI group. The presence of amoxicillin-resistant Enterococcus faecium was the main reason for inappropriate antibiotic therapy, as confirmed in earlier findings (5,23,24). A combination of piperacillin/tazobactam with amikacin was the most widely prescribed empirical antibiotic therapy. It was administered to approximately fifty percent of patients. For CA-IAI patients, this treatment is in accordance with French and International guidelines, although the benefit of aminoglycosides is not proven in this indication (2,3,25,26). As regards HA-IAI patients, carbapenems are currently proposed in guidelines when specific conditions are found (2,3). Otherwise, piperacillin/tazobactam is indicated, possibly in conjunction with an aminoglycoside and/or vancomycin. Inadequate empirical antibiotic treatment is associated with poor prognosis, increased morbidity and mortality rates, reoperation and prolonged ICU or hospital stays (21,27–30).
Our study has several limitations. Firstly, this is a retrospective study with missing data. The time between diagnosis, antibiotics and surgery was, for instance, not consistently recorded in the medical records. Secondly, the patients were admitted to two hospitals only, making it difficult to extrapolate our findings. Thirdly, not all patients gave a peritoneal sample prior to surgery, particularly in the CA-IAI group. As mentioned above, the impact of the initial antibiotic on the microbiological findings, which is generally associated with good outcome in terms of mortality rates or complications, was not analysed in our study. This situation had been already reported in another study, and the rate of peritoneal sampling needs to be improved as recommended in current guidelines (23,31,32).