Luisa Sodano, Clotilde Serafini (Azienda Ospedaliera “San Camillo-Forlanini”, Roma), Nicola Petrosillo, Lorena Martini, Giuseppe Ippolito (Istituto Nazionale delle Malattie Infettive “Lazzaro Spallanzani”, Roma), Antonio Campopiano, Michele Ferrari (Università “La Sapienza”, Roma)

In Italy, it is estimated that 450,000-700,000 cases of hospital infection occur annually, representing an incidence of 5-8%. The number of annual deaths due to such infections is estimated at 4500-7000 per year.

 In many settings, surgical services have elevated rates of hospital-related infections. In view of the elevated general risk as well as the planned opening of a heart transplant service, active surveillance was initiated in March 2000 in the cardiosurgical unit and its associated intensive care unit at the San Camillo Hospital in Rome using guidelines suggested in the United States Centers for Disease Control and Prevention’s (CDC) National Nosocomial Infection Surveillance System (NNIS) (1). The case definition for nosocomial infections was the same used in NNIS, with the exception of the definition for pneumonia, which follows that set forth in the 1997 European hospital infection protocol, HELICS (2). For surgical site infections (SSI), surveillance was extended for 30 days following the procedure. Following NNIS guidelines, the index of the risk of SSI infections for each patient was based on the severity of illness (as measured by the Anesthesiology Score of America) and type and duration of the procedure (3).

 Between March and December, 2000, surveillance was conducted on 646 cardiovascular surgery patients, who had a median age of 67 years. A total of 59.4% underwent coronary artery bypass graft (CABG), and 34.8% had valvular surgery. Of the 646 patients, 5.9% were emergency admissions; 4.6% died.

 Among the 642 patients who remained in the hospital for at least two days following their surgical procedure, 74 nosocomial infections were detected in 64 patients. the incidence of infection was 11.5% and the incidence of patients with at least one infection was 10%. Calculated as rates per 1000 hospital days (n = 6744), the incidence rates were 11.0/1000 and 9.5/1000 days, respectively.

 Of the 74 infections, 61% were SSIs, 19% were bloodstream infections, 14% were pneumonias, 5% were urinary tract infections, and the remaining 1% involved other sites. Forty percent (18/45) of the SSIs were detected after discharge.

SSIs occurred in 8.1% of the 384 who underwent CABG and 3.1% of the 225 who underwent valvular surgery. SSI rates increased with the index of the risk of infection, with infections observed in 4.2% of patients who had an index of 0, 6.7% of those who had an index of 1 and 9.34% of those with an index of 2 or 3.

Analysis of temporal trends of SSIs demonstrate that the highest rates of infection per 100 patients occurred in April (concentrated in the week before Easter) and during the summer months .

Micro-organisms were isolated in 54 of the infections. Of the 76 micro-organisms isolated, 49% were Gram-positive and 46% Gram-negative. Thirty-two percent (24/76) of the organisms isolated were Staphylococcus aureus, 14% (11/76) Pseudomonas aeruginosa, and 12% (9/76), were coagulase-negative Staphylococcus. Oxacillin resistance was found in 54% of the Staphylococcus aureus and 78% of the coagulase-negative isolates.

The most commonly used antibiotics for prophylaxis were cefazolin (66%) and amoxacillin + clavulinic acid (26%). The median duration of prophylaxis was three days, which was exceeded in 157 patients.

The authors wish to thank Prof. Francesco Musumeci and Dr. Antonio Menichetti, as well as the head nurses Carmela Fadda, Goffredo Marignetti and Noemi Vincenzi for their collaboration.

Editorial Note:

Dr. William R. Jarvis, Hospital Infections Program, Centers for Disease Control and Prevention, Atlanta, GA, USA

Throughout the developed world, cardiac catheterization and cardiac surgery are among the most commonly performed surgical procedures in the 15-74 age group (4). The large population of patients undergoing cardiac surgery (CABG or valvular procedures) is at risk of healthcare-associated infection. As was observed in this study, the most common infections in cardiovascular surgery patients are infections of the surgical site, followed by bloodstream infections and pneumonia.

Established programs for surveillance and control of SSIs in cardiac surgery patients have been demonstrated to be cost-effective. Previous studies have documented that the major risk factors for SSI in cardiac surgery patients include pre-operative preparation (shaving of the patients being a major risk factor), severity of illness (often measured by the Anesthesiology Score of America), duration of the procedure, donor site, and intrinsic host factors–particularly age, obesity, and diabetes. Appropriately administered prophylactic antimicrobials are protective. Often, many of these factors are captured through the use of risk indexes (5,6). Subsequent stratification of risk of infection by risk index facilitates intra-hospital comparisons of infection according to different procedures and inter-hospital comparisons of the same procedures. As observed in the study reported above, the risk of SSI increases with the patient’s risk index. These data also show that a risk index can be used to identify high-risk patients immediately after the surgical procedure is performed and additional prevention interventions can be implemented.

Surveillance of healthcare-associated infections requires the use of standardized definitions and surveillance protocols. For instance, use of different definitions will led to differences in infection rates (7). One of the challenges in conducting surveillance of SSIs in cardiac surgery patients is the issue of post-discharge surveillance, which in this study accounted for 40% of the infections. A number of studies have shown that post-discharge surveillance of cardiac surgery patients does detect more infections. However, post-discharge surveillance is time-consuming and the methodology (contacting the patient or surgeon, use of postcards, etc.) is not standardized. Infection control personnel at each institution need to determine if and how such post-discharge surveillance will be done.

The reasons behind the seasonal incidence observed in this study are unclear. Possible explanations include a lower frequency of elective procedures during holiday periods, with a concomitantly higher index of risk among the patients, or alternatively differences in staffing patterns. In the United States, a clear link has been established between levels of staffing in ICUs and levels of SSIs (8).

One of the major ways to reduce the risk of SSI during cardiac surgery is the appropriate use of antimicrobial prophylaxis. The correct agent needs to be given at the correct time. The agent should be given so that peak tissue levels are present at the time of the first incision. Thus, administration of the agent at the time the patient is called from the floor or when waiting in the anesthesia area may be too early. Standardization of the agent to be given and having the anesthesia personnel give the agent during induction of anesthesia may be the easiest to monitor.

Selected addition methods to reduce the risk of SSI in cardiac surgery patients include avoiding prolonged hospitalizations before surgery, pre-operative cleaning with an antibacterial soap, either not shaving the patient or using clippers rather than razors (which nick the skin and provide access to bacteria), making sure that the blood sugar of diabetic patients is carefully controlled, not performing elective surgery on patients with remote infections, insuring that operative technique is scrupulous, reducing the number of people entering and exiting the room and involved in the procedure, and changing gloves between obtaining veins from the donor site and beginning the mediastinal incision. Cardiac surgery is a very complicated and requires careful attention to infection prevention efforts throughout the course of the patient.

Studies such as described here show the value of conducting surveillance for SSIs in cardiac surgery patients. Such measures provide an indication of the rate of infection compared with other benchmark rates, they provide a rate to compare future interventions, and provide the patients with a rough estimate of their infection risk. The use of such data to guide prevention interventions and to assess the effectiveness of the interventions should be the goal of infection prevention and control programs.

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