High Prevalence of VIM,KPC,and NDM Expression among Surgical Site Infection Pathogens in Patients Having Emergency Surgery

Abstract

Background:

The rate of surgical site infection (SSI) in patients who undergo emergency operations is higher than in other patients. Previous studies showed an increasing role of gram- negative pathogens (GNP) in SSI. We aimed to identify GNP causing SSIs after emergency surgery, to characterize the carbapenemase-resistance genes in carbapenem-resistant pathogens (CRPs), and to identify the risk factors for SSI caused by CRP.

Method:

We conducted a one-year prospective study from September 2014 in the Emergency Hospital of Cairo University Hospitals. Surveillance for SSIs was conducted according to the case definitions of the U.S. Centers for Disease Control and Prevention. Clinical specimens from patients suspected of having SSI were collected; pathogens were identified by Bruker matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectometry. Antimicrobial susceptibility was tested by the VITEK-2 and E-test. Carbapenem-resistant GNPs were characterized by multiplex polymerase chain reaction for IMP, VIM, SPM, OXA-48, NDM, KPC, BIC, AIM, GIM, SIM, and DIM. Clinical data for patients with SSI infected with CRP were compared with the non-infected patients for detection of risk factors.

Results:

Surgical site infection affected 6.7% of patients who had emergency operations, and GNP represented 85% of these pathogens. Carbapenem-resistant pathogens caused 61% of the SSI, including all those caused by Acinetobacter baumannii, 70% of those caused by Pseudomonas aeruginosa, and 67% of those caused by Klebsiella pneumoniae. The PCR revealed that VIM, KPC, and NDM were the most common resistance genes. Risk factors for SSI were previous hospitalization, longer hospital stay, type of surgical incision, and abundant drainage; whereas previous hospitalization and infection by non-enteric environmental GNP were the risk factors for SSI caused by CRP.

Conclusion:

The rate of SSIs caused by CRP was high after emergency surgery. VIM, KPC, and NDM were the most commonly found genes. Prior hospitalization and infection by non-enteric GNP were risk factors, which can be mitigated by eradication of bacterial populations in environmental reservoirs and control of transmission.

Surgical site infection (SSI) is one of the most frequent types of healthcare-associated infection. It increases the burden on the patient, family, and healthcare system. Abdominal surgery is commonly followed by such complications as SSI, especially after emergency operations with contaminated and dirty wounds [1, 2]. Emergency procedures do not allow the standard pre-operative preparation such as confirmation of stable vital signs, adequate antiseptic skin preparation, and decontamination of the colon before colon surgery [3], thus increasing the risk of SSI.

Hospital environments can be reservoirs for multi–drug-resistant bacteria including carbapenem-resistant gram-negative pathogens (CR-GNP). In Egypt, high-level antimicrobial resistance is alarmingly common; e.g., all Acinetobacter spp. isolates from hospital-acquired infections (HAIs) in Egypt are multi-drug-resistant, and 84% are carbapenem-resistant [4, 5].

Carbapenemases are classified into Ambler's class A, B, or D enzymes. Class A Klebsiella pneumoniae carbapenemases (KPCs) can be detected by ertapenem [6]. Other clinically important carbapenemases are the class B metallo-β-lactamases (MBLs; e.g., NDMs, IMPs, VIMs) and the class D OXA-type carbapenemases (e.g., OXA-23 in A. baumannii and OXA-48 in K. pneumoniae). These carbapenemase genes are borne on plasmids, which facilitates their intraspecies and interspecies dissemination [7].

Identification of carbapenemase-producing GNP can be done by either phenotypic or molecular methods. Multiplex polymerase chain reaction (PCR) was used for rapid and precise identification of carbapenemase genes in most studies [8].

The aim of this study was to identify GNP causing SSIs after emergency surgery, detect the carbapenemase-producing genes in CRP, and identify the risk factors for SSI caused by CRP.

Patients and Methods

Study design

This prospective case-control study for surveillance of SSI was done in an emergency university hospital over a period of 12 months starting in September 2014. The study included 851 patients who were admitted to the hospital; 489 of these patients (57%) had operations. We enrolled all SSI patients and a control group of 66 age- and sex-matched patients who had a surgical history but did not develop SSI.

Clinical data

From all enrolled cases and controls, we collected demographic data (age, sex), length of stay (LOS), previous hospitalization, co-morbidities, Acute Physiology And Chronic Health Evaluation (APACHE) II score for adult patients. We used the U.S. Centers for Disease Control and Prevention case definitions for SSI [9].

Sample collection

Clinical specimens from patients with suspected SSIs were collected and cultured.

Microbiology techniques

We identified pathogens by Bruker MALDI-TOF (Bruker, Daltonics) and tested their susceptibility by VITEK-2 compact (BioMérieux, Marcy l'Etoile, France). The minimum inhibitory concentration (MIC) of etrapenem was measured by the E-test (BioMérieux) [10].

Molecular testing

The DNA were extracted from isolates with reduced carbapenem susceptibility by the boiling method [11] followed by multiplex conventional PCR to detect 11 carbapenemase genes according to Poirel et al. [8].

Statistical analysis

Coded data were entered in the computer using the 2010 Microsoft Office Excel program for Windows. Data were then transferred to the Statistical Package for the Social Sciences program, version 23 (SPSS Statistics for Windows, Version 23.0; IBM, Armonk, NY) to be analyzed.

Comparison between groups was performed using the Mann-Whitney test for quantitative variables and the χ² and Fisher exact test for qualitative ones.

Multi-variate logistic regression models were conducted to explore the predictors of SSIs. P values ≤0.05 were considered statistically significant.

Results

Among the 489 patients, the overall SSI rate was 6.7% (33 patients), of which 48% were deep infections. Most SSIs occurred after abdominal surgery (61%), neurosurgery (18.2%), or orthopedic surgery (15.2%). The most common surgical incision type was contaminated–dirty (20/33; 60.6%).

The median age of infected patients was 55 years; male patients represented 73% of the total. The median length of hospitalization was 13 days. Risk factors for SSI are listed in Table 1.

Table 1.

Risk Factors for Surgical Site Infections

Risk factor	Patients with SSI (n = 33)	Control group without SSI (n = 66)	p
Median age (IQR)	55 (35.0–63.0)	37.5 (30.0–60.0)	0.2
Sex
Male (%)	24 (72.7)	43 (65.2)	0.501
Female (%)	9 (27.3)	23 (34.8)
Median APACHE II score (IQR)	17 (14.0–23.0)	17 (14.0–23.0)	0.990
Median LOS (IQR)	13 (7.0–19.0)	19 (14.0–33.0)	0.015
More than one device inserted (%)	30 (90.9)	50 (75.8)	0.104
Previous hospitalization (%)	30 (63.6)	50 (22.7)	<0.001
Co-morbidities (%)	17 (51.5)	31 (47)	0.677
History of diabetes mellitus (%)	9 (27.3)	9 (13.6)	0.107
Surgical incision type
Clean/clean-contaminated (%)	13 (39.4)	50 (75.8)
Contaminated/dirty (%)	20 (60.6)	16 (24.2)	0.001
History of trauma (%)	11 (33.3)	42 (36.4)	0.826
History of drain insertion (%)	22 (66.7)	25 (37.9)	0.010
Crude mortality rate (%)	17 (51.5)	32 (48.5)	0.960

Statistically significant values are in boldface type.

APACHE = Acute Physiology and Chronic Health Evaluation; IQR = interquartile range (range between 25^th–75^th percentiles); LOS = length of hospital stay.

SSI risk factors

Multivariable analysis indicated that the risk of developing SSI was higher with previous hospitalization (odds ratio [OR] 7.47; 95% confidence interval [CI] 2.3–24.26; p = 0.001), drain insertion (OR 4.16; 95% CI 1.33–12.99; p = 0.014), and length of hospital stay after surgery (OR 0.85; 95% CI 0.78–0.92; p < 0.001).

Microbiology of SSIs

About 85% of the SSIs were caused by GNP. The most prevalent causative organisms were Pseudomonas spp. (30%) and Acinetobacter baumannii and Klebsiella spp. (18% each). Methicillin-resistant Staphylococcus aureus (MRSA) caused 15% of the SSIs.

Risk factors for CRP

The risk factors for SSI caused by carbapenem-resistant pathogens were previous hospitalization (odds ratio 8.17; 95% CI 1.42–47.01; p = 0.019), whereas infection caused by non-fermenting pathogens (OR 5.688; 95% CI 1.07–29.9; p = 0.042) and Acute Physiology and Chronic Health Evaluation (APACHE) II score provided an objective means of predicting death in the intensive care unit (ICU). The higher APACHE II score was not a risk factor for infection with CRP (Table 2).

Table 2.

Risk Factors for Carbapenem-Resistant Pathogen-Caused Surgical Site Infections

Risk factor	Carbapenem-resistant isolates (n = 17)	Carbapenem-sensitive isolates (n = 11)	p
Median age (IQR)	57.5 (33–66)	55 (35–63)	0.90
Male/female (%)	11 (65)/6 (35)	9 (82)/2 (18)	0.296
Median APACHE II score (IQR)	14 (12–23)	21 (17–28)	0.049
Median LOS (IQR)	15 (7–34)	9 (5–18)	0.303
More than one device inserted (%)	16 (94)	10 (91)	0.664
Previous hospitalization (%)	14 (82)	4 (36)	0.019
Co-morbidities (%)	7 (41)	8 (73)	0.106
History of diabetes mellitus (%)	4 (24)	5 (45)	0.212
History of cardiac disease (%)	1 (6)	2 (18)	0.336
History of renal disease (%)	2 (12)	1 (9)	0.664
History of hepatic disease (%)	1 (6)	2 (18)	0.336
Surgical incision type
Clean/clean–contaminated (%)	4 (24)	4 (36)	0.376
Contaminated–dirty (%)	13 (76)	7 (64)	0.376
History of antibiotic use before SSI (%)	14 (82)	6 (55)	0.249
History of carbapenem use before SSI (%)	14 (82)	6 (55)	0.123
Causative pathogen
Enterobacteriaceae (%)	4 (24)	7 (64)	0.042
Non-fermenter (%)	13 (76)	4 (36)	0.042
History of trauma (%)	4 (24)	3 (27)	0.581
History of drain use (%)	11 (65)	8 (73)	0.493
Crude mortality rate (%)	10 (59)	6 (55)	0.565

Statistically significant values are in boldface type.

APACHE = Acute Physiology and Chronic Health Evaluation; IQR = interquartile range (range between 25^th–75^th percentiles); LOS = length of hospital stay.

Carbapenem resistance and carbapenemase producers

Among GNP, 61% showed reduced carbapenem sensitivity, including all A. baumannii, 70% of P. aeruginosa, and 67% of K. pneumoniae. All Escherichia coli and Providentia recovered were carbapenem sensitive.

VIM was the most often detected gene followed by KPC and NDM (40% and 20% for each). One isolate was positive for both KPC and NDM (10%), and SIM was positive in one isolate. All isolates were negative for the other screened genes (Fig. 1).

FIG. 1.

Correlation between pathogens and detected carbapenemase genes. Carbapenemase genes examined were IMP, VIM, SPM, OXA-48, NDM, KPC, BIC, AIM, GIM, SIM, and DIM.

Discussion

Surveillance studies conducted in Egypt showed that GNPs were the commonest causes of HAI [5]. Our study confirms the predominance of GNP in SSIs; this probably is because the majority of our emergency operations were abdominal, and high numbers of GNP inhabit the intestines but less often are present on the patient's skin [3, 12].

The univariable analysis showed that the LOS, previous hospitalization, the type of incision, and abundant post-operative drainage were statistically significantly greater among patients with SSIs. This is in accordance with previous studies [12, 13].

Carbapenem resistance was significantly common among GNP of patients with previous hospitalizations, as were SSI caused by non-fermenting bacteria (P. aeruginosa and A. baumannii). Exposure to the hospital environment is a known risk factor for colonization and infection by CRP. Preventing transmission and eradication of reservoirs of CRP is a major infection prevention priority [14]. In agreement with our results, Clina et al. reported GNP in SSIs including P. aeruginosa, and resistance was higher among isolates from ICU patients [15].

Pseudomonas aeruginosa was isolated in 33% of our patients, of which 70% had reduced carbapenem sensitivity, and 71% produced carbapenemases. VIM was detected in 80% of Pseudomonas. This confirms a previous study by Zafer et al., who reported that carbapenem-resistant P. aeruginosa was isolated in Egypt from different clinical specimens, including surgical incisions with a high prevalence of VIM [16]. Other studies reported that VIM carbapenemase is a predominant mechanism for resistance to carbapenems in P. aeruginosa [17, 18].

In our study, 41% of the carbapenem-resistant GNPs were negative for carbapenemase genes, including 71% of A. baumannii and 29% of P. aeruginosa. This is in keeping with other studies [19, 20], where other resistance mechanisms; e.g., decreased expression of porin (oprD) and overexpression of the MexAB-OprM, MexEF-OprN, and MexCD-OprJ efflux systems, dominated [21].

In our study, one K. pneumoniae isolate showed both KPC and NDM. The presence of multiple resistance genes and mechanisms was previously reported [22].

Conclusion

Gram-negative pathogens were the commonest causes of SSIs among patients having emergency surgery. Carbapenem-resistant pathogens were predominant and frequently carried carbapenemase genes. To control SSI, we identified a system to prioritize preventive interventions, namely, eradication of the reservoirs by intensive cleaning and disinfection and prevention of transmission by reinforcement of infection prevention and control practices.

Footnotes

Acknowledgments

We thank all data collectors and the participants in this study. No funding was available for this work.

Author Disclosure Statement

No competing financial interests exist.

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