Bacterial Infections
Table 2: Important Human Pathogens where Therapeutically Important Antimicrobial Resistance has Emerged Bacterial Species
Antimicrobial
Community S. aureus
S. pneumoniae S. pyogenes
Haemophilus influenzae Neisseria gonorrhoeae
Salmonella spp, including typhoid/paratyphoid V. cholera E. coli
Healthcare Facility S. aureus
Enterococci spp
ESBL Enterobacteriaceae K. pneumoniae P. aeruginosa
Acinetobacter spp Clostridium difficile
Penicillin, methicillin, macrolides, clindamycin
Penicillin, macrolides, TMP/SMX, tetracycline, fluoroquinolones Macrolides Ampicillin
Penicillin, tetracycline, fluoroquinolones
Chloramphenicol, tetracyclines, ampicillin, TMP/SMX, fluoroquinolones Tetracycline, TMP/SMX, cholaramphenicol Ampicillin, TMP/SMX, fluoroquinolones, ESBL
Methicillin, vancomycin, linezolid Vancomycin
Penicillins, cephalosporins, fluoroquinolones Carbapenems, other β-lactams, fluoroquinolones Fluoroquinolones, aminoglycosides, β-lactams Carbapenems, fluoroquinolones, tigecycline Fluoroquinolones, metronidazole
ESBL = extended spectrum β-lactameses; TMP/SMX = trimethoprim/sulfamethoxazole.
A very high prevalence of resistant organisms is reported in some nursing homes.25,28
common in this setting.25
MRSA, VRE and ESBL-producing organisms are More recent reports describe increasing
isolation of A. baumanii in some US long-term care facilities.28 However, residents from whom resistant organisms are isolated are usually colonised and infection is infrequent. For some organisms, such as MRSA or VRE, colonisation persists for years. Consistent resident risk factors for isolation of resistant organisms include the presence of invasive devices, recent antimicrobial therapy, a greater number of comorbidities, impaired functional status and recent exposure to an acute care facility. The majority of these resistant organisms, in fact, are acquired in acute care facilities and introduced into the long-term care facility with the transfer of the resident.
Impact of Antimicrobial Resistance Individuals colonised with resistant organisms do not usually experience any adverse effects. Infection with an antimicrobial-resistant organism potentially increases morbidity and mortality due to delayed or inadequate antimicrobial therapy and it also increases healthcare costs. Few reports rigorously address the excess morbidity attributable to resistance in the community.29
Failure of β-lactam therapy for community-acquired MRSA infections8 or E. coli in acute cystitis when the organism is resistant to empiric therapy are well described and result in prolonged symptoms requiring further healthcare evaluation for some patients. Some deaths have occurred in patients with community-acquired MRSA infection treated with β-lactam antimicrobials.8
Studies on the impact of antimicrobial resistance in healthcare facilities are, of necessity, case-control studies and subject to bias. This is because the risk factors that are associated with antimicrobial resistance, such as greater acuity, are also consistently independently associated with prolonged stay and increased mortality.30–32
Studies
have usually reported excess mortality, increased length of stay and increased costs associated with antimicrobial resistance.24,32,33
There is still effective antimicrobial therapy for most bacteria causing human illness, but antimicrobial agents required to treat infections with
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resistant organisms are usually more expensive, may have increased toxicity and may require parenteral rather than oral administration. There is an even greater burden of antimicrobial resistance in developing countries, when infections cannot be treated because of inability to access effective antimicrobials due to cost or lack of availability.
Management
Antimicrobial resistance cannot be fully prevented. However, a multifaceted approach is recommended to limit the emergence of new resistance, prevent transmission of resistant organisms and minimise negative outcomes.
Surveillance
The goals of global surveillance are to identify new resistance among previously susceptible strains, to measure prevalence of resistance and to monitor spread. At the local level, knowledge of the presence and extent of antimicrobial resistance for clinically-important species in community and healthcare facilities guides therapeutic decisions for empiric antimicrobial therapy.37
Surveillance for antimicrobial-resistant bacteria is important globally and locally.34–36
There is, however, potential bias when interpreting results from surveillance studies.38
Laboratory-based surveillance systems invariably
incorporate specimens from patients who are more severely ill or have failed therapy, so higher resistance rates are reported than may be present in the larger community. Rempel and Laupland38
summarise
issues to consider in interpreting the reliability of surveillance data. These include:
• denominators used; • case definitions; • case ascertainment; • sampling bias; •
handling of multiple specimens from the same patient; and
• laboratory practices and procedures. Public Health Interventions
Optimal public health practice will limit bacterial transmission and prevent infection, resulting in lower antimicrobial use. Specific
EUROPEAN INFECTIOUS DISEASE
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