Neurosurgery always involves the opening of the central nervous and CSF circulatory systems and causes blood-brain barrier destruction, which easily leads to HAM. In keeping with our findings, previous studies with a smaller number of HAM patients have also found predictors to reduce the mortality ratio. However, this cohort originated from the largest HAM database in China, with the most representative epidemiology. We first summarize the clinical and microbial epidemiology in patients with HAM, and the predictors for 90-day mortality account for confounding by indication through the use of Cox propensity score modeling. To the best of our knowledge, this is the largest and longest cohort of patients with HAM in which a survival analysis has been evaluated.
The pathogens that cause HAM are mainly bacteria. In our study, the proportion of HAM cases caused by GNB was higher than that caused by GPB, and the proportion of gram-negative bacteria in the non-survivor group was significantly higher than that of the gram-positive bacteria, similar to reports in the literature[8]. The majority of multidrug-resistant bacteria, which always lead to poor outcomes in patients because of severe infection, are gram-negative bacteria, such as carbapenem-resistant Enterobacteriaceae (CRE), extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, carbapenem-resistant Acinetobacter baumannii (CRAB), and carbapenem-resistant Pseudomonas aeruginosa (CRPE). There is a high mortality rate in the treatment process due to the lack of sensitive antibiotics. A follow-up study indicated that infections caused by gram-negative bacteria do have certain sequelae effects, and better antibiotic care is urgently needed[9]. Drug resistance is a very important factor in patients with infections, and a number of studies have shown that different mechanisms of drug resistance have significant differences in the outcomes of multiple infections[10]. For example, ESBL production is a critical risk factor for sepsis caused by Enterobacteriaceae[11]. Another Spanish study showed that CRE infection significantly affected the mortality of sepsis patients[12]. The results of our study showed that, except for VRE, the proportion of drug-resistant bacteria in the non-survivor group was significantly higher than that in the survivor group.
We observed significant mortality in patients with HAM, and the mortality rate in our study was higher than that in previous reports[13, 14]. HAM patients with adverse outcomes, had greater levels of hypertension, EVD and LD than those of surviving patients. Furthermore, the reoperation rate was significantly higher in surviving patients. Hypertension is one of the inducers of immune system diseases. For example, pulmonary hypertension is closely related to immune suppression[15, 16]. Compared with healthy people, the immunity of hospitalized patients has a downward trend, and hypertension will aggravate the occurrence of this situation and lead to a poor outcomes[17]. Similarly, hypertension can induce some inflammation[18], and the presence of strong inflammation in patients, such as a “cytokine storm”, will increase the difficulty of clinical treatment. Therefore, hypertension, as an independent predictor for survival in HAM patients, has a certain theoretical basis. EVD and LD are common operations in neurosurgical patients, and they have similar clinical characteristics. HAM caused by both of them are catheter-related infections. Catheter-related infections are an important cause of patient death[19], and EVD is also an independent predictor for craniotomy. Impurity eyewinker entry is one of the major causes of infection, and if antibiotics are not administered in time, bacteria will adhere to the catheter, and bacteria such as Pseudomonas aeruginosa that can form biofilms can have serious consequences[20]. As an independent protective factor, reoperation is an interesting discovery. In conventional circumstances, reoperation means that doctors cannot solve the surgical problem by a single operation, and reoperation has certain anatomical significance in the treatment of infection, such as exposing the bacterial storage site, so reoperation should be taken seriously or employed as a protective factor.
Previous reports have shown that antibiotic prophylaxis can effectively reduce infection occurrence[21]. Our research also supports this theory. Up to 80% of HAM patients received antibiotic prophylaxis. The use of antibiotic prophylaxis in the survivor group was significantly higher than that in the non-survivor group (P = 0.001). Nevertheless, empirical treatment and precise treatment and the choice of antibiotics are closely related to patient mortality.
In infectious patients, several retrospective studies targeting multiresistant bacteria have recommended improved survival in patients receiving two or more combinations of active antibiotics in vitro, mostly in patients with high risk of mortality[22]. It has been reported that compared with single drug usage, multidrug combinations can have a better cure rate for certain infections[23, 24]. However, there are also reports showing that for some special drug-resistant bacterial infections, multidrug combinations cannot achieve expected results[25, 26], as has been shown in recent clinical trials. In our study, we recommended that dual-drug combinations and triple-drug combinations are statistically significant in empirical treatment (P = 0.013) and precise treatment (P = 0.001) of HAM. The mortality rate of patients with triple drug combinations is lower. However, the synergistic effect of different antibiotics on HAM still needs further exploration and research.
Our study has some limitations. First, it is a retrospective study in a single center, although it is the largest HAM series from the China nosocomial meningitis database reported thus far. Second, the molecular epidemiology of the patients’ infections and drug resistance genes were not analyzed, which may have certain shortcomings for precision drug therapy.