National Collaborating Centre for Infectious Diseases / Centre de collaboration nationale des maladies infectieuses

Knowledge that's contagious!

Tel: 204.943.0051
E-Mail: nccid@icid.com

Antimicrobial-Resistant Organisms

Expert Opinion

During the 1990s, antibiotic resistance increased dramatically and is acknowledged to be one of the most serious threats to the treatment of infectious diseases. Because of this, the World Health Organization issued a stark warning in a report, "Overcoming Antimicrobial Resistance." In addition to large increases in costs and greater toxicity of newer drugs, antibiotic-resistant organisms are continuously eroding current drugs, leaving few or no alternative agents. 

Controlling antimicrobial resistance is difficult and requires a multifaceted approach, including reducing unnecessary drug prescribing for both humans and animals, reducing transmission of resistant organisms through enhanced infection control and environmental hygienic practices, and identifying trends in resistance through surveillance. Overuse of antibiotics is considered the major factor in the emergence and spread of antibiotic resistance and achieving the appropriate ecologic balance by judicious use is the key factor in overcoming the resistance challenge.

Dr. John Conly

Key Publications

Conly J. Antimicrobial resistance in Canada. CMAJ 2002; 167: 885-91.
Canadian Programs in Antimicrobial Resistance

The Canadian Nosocomial Infection Surveillance Program (CNISP) reports laboratory-based surveillance data on many hospital-associated pathogens including MRSA, VRE and C. difficile from 49 reporting sites. 

The Antimicrobial Resistance and Nosocomial Infections Laboratory at the National Microbiology Laboratory in Winnipeg provides molecular testing of both hospital- and community-acquired strains of MRSA, VRE, and ESBLs. 

The Canadian Committee on Antibiotic Resistance (CCAR) provides information and guidance documents on prevention activities for the reduction of antimicrobial resistance in both human and animal health. 

The Canadian Antimicrobial Resistance Alliance (CARA) provides online data from several surveillance studies of antimicrobial resistant organisms as well as educational resources on antimicrobial resistance. 

The Canadian Integrated Program on Antimicrobial Resistance Surveillance (CIPARS) is a federal program for surveillance of enteric pathogens in both human and animal environments, including data collected from farm, retail food, and clinical sites. 

The Community Hospital and Infection Control Association (CHICA) provides guidance for infection control programs via their member associations across the country. A number of excellent AMR resources are listed.

Methicillin-Resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus is the most common cause of skin infections including boils and cellulitis, but more severe infections may occur, including pneumonia, blood and bone infections. Most S. aureus is resistant to beta-lactam antibiotics such as penicillin and amoxicillin due to the production of a beta-lactamase enzyme. If S. aureusdevelops resistance to the semisynthetic (or antistaphylococcal) beta-lactam antibiotics, cephalosporins and carbapenems due to a mutated penicillin binding protein, it is described as methicillin-resistant Staphylococcus aureus (MRSA). MRSA was first reported in the hospital setting, but resistant strains have also emerged in the community. Strains which evolve resistance in the community are generally susceptible to a wider range of antibiotics, but in recent years the distinction between hospital- and community-acquired strains is becoming blurred as organisms are transferred in and out of the health care environment. According to the 2006 CNISP results, the overall incidence rate for MRSA was 8.04 per 1,000 admissions (2.7 for infection and 5.34 for colonization). Of the 5,787 new cases identified in 2006, 77% were healthcare-associated (either hospital or long-term care facilities) and 15% were community-acquired. 

The prevalence of MRSA is rapidly increasing in Canada. MRSA rates in the U.S. have been climbing for many years, and have now reached 60% in many regions. Five characteristics contribute to the acquisition of staphylococcal infection (and MRSA where present), known as the 5 C's: Crowding, Contact (skin-to-skin), Compromised (broken skin), Contaminated (shared items or surfaces), and Cleanliness (lack of). MRSA is a more serious concern among populations where these factors are common such as in correctional facilities, on sports teams, and among groups such as intra-venous drug users. 

Vancomycin Resistant Enterococcus (VRE)

Enterococci are found the gastrointestinal tract of most individuals but can also be present in the anterior urethra, vagina, skin, oropharynx and/or bile. Enterococci may also colonize wounds, ulcers and medical device sites in hospitalized patients, and is a common cause of health care-associated infection. Some strains ofEnterococcus faecium and Enterococcus faecalis have developed resistance to high levels of the antibiotic vancomycin. 
CNISP surveillance data show that VRE rates in Canada remain low. Between October 1998 to 2005 3037 new cases were identified with an estimated infection rate of 6.3%. Rates increased over the seven years from 0.37 per 1,000 patient admissions in 1998 to 1.32 per 1,000 patient admissions in 2005, a 3.6 fold increase. 

Risk factors for VRE acquisition include severity of underlying illness, presence of invasive devices, antibiotic use and length of hospital stay. VRE is most commonly spread via the transiently colonized hands of health care workers who acquire it from contact with colonized or infected clients/patients/residents, or after handling contaminated material or equipment. Hospitalized patients with gastrointestinal carriage of VRE are the major reservoir.

Extended-Spectrum Beta-Lactamase (ESBL) producing organisms

Members of the Enterobacteriaceae family of bacteria, including Escherichia coli and Klebsiella pneumoniae may express plasmid-encoded genes for beta-lactamase enzymes with the capacity to hydrolyse all of the beta-lactam antibiotics, including third generation cephalosporins and aztreonam. Plasmids containing ESBLs often contain other genes for antimicrobial resistance, further limiting treatment options for infections caused by these organisms. 

Of particular concern is the increase in prevalence of CTX-M-class ESBL-producing E. coli in both hospital and community settings. These organisms harbour resistance to multiple classes of antimicrobials, including most first-line therapeutic agents and most oral antimicrobials, which severely limits outpatient treatment options. 

Recent Documents

Recent Publications