Pencillin Resistance Rates Stabilizing
| For purposes of year-to-year comparison, the CBSN routinely evaluates antibiotic resistance
to Streptococcus pneumoniae (also known as Strep pneumo). Over the past five years,
resistance to penicillin has hovered at about 15 percent, suggesting that rates may have stabilized.
Strep pneumo is the main cause of infections such as bronchitis, sinusitis, middle ear
infections and pneumonia. Each year in Canada, it accounts for 12,500 cases of pneumonia requiring
hospitalization.
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Macrolide Resistance Rates on the Rise
| CBSN
data demonstrate a steady increase in macrolide resistance
since 1999.
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Strep pneumo resistance to erythromycin
(a commonly prescribed macrolide) increased from 18.0
percent in 2004 to 19.3 percent in 2005 (Fig. 2), which
in 1999 it stood at just under 10%. According to Dr.
Donald Low, "the rate of erythromycin resistance
has almost doubled in the last six years, a trend that
has to be watched closely." |
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Effect of the Newer Fluoroquinolone
| The striking increase
observed in fluoroquinolone resistance over the years of the study,
especially in respiratory isolates from patients >64 years of age,
declined for the first time in 2003 and appears to have stabilized.
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What accounts for the fluoroquinolone class being able to maintain
low S. pneumoniae resistance rates in spite of increased use?
Two factors that emerged in 2000 may help explain this phenomenon
and why it has happened in North America. First, the introduction
of new fluoroquinolones with enhanced gram-positive activity and
second, the introduction of the pneumococcal conjugate vaccine
(PCV). These two factors may be acting synergistically to reduce
selective pressure that would, unchecked, lead to the emergence of
resistant S. pneumoniae mutations.
In 2000, two potent respiratory quinolones moxifloxacin and
gatifloxacin, with their increased activity against S. pneumoniae were
introduced in North America. Before moxifloxacin and gatifloxacin, ciprofloxacin and levofloxacin
had been widely used to treat respiratory tract infections but their
borderline pneumococcal activity appeared to lead to poor eradication
rates and increased pneumococcal resistance. As cipro.oxacin and
levo.oxacin began to be replaced by the newer fluoroquinolones in
the treatment of respiratory tract infection, pneumococcal resistance
to the class as a whole began to stabilize.
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Antibiotic Use as a Predicator of
Antibiotic Resistance
| A recent history of antibiotic use
increases the risk of resistance in the infecting isolate, particularly within the class of
antibiotics (Figure 3). Prior receipt of any antibiotic increases the chance that an infecting isolate
will be resistant to penicillins or cephalosporins. Prior use of macrolides, trimethroprim-sulfamethoxazole
or levofloxacin is associated primarily with a class-specific effect: that is, a patient who has previously
been given a macrolide antibiotic is much more likely to have a macrolide resistant isolate, than a patient who
has received any other class of antibiotic.
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| Knowledge of prior antimicrobial use is crucial for determining appropriate therapy for
suspected pneumococcal infection. The most important risk factor for resistance to an antibiotic
is previous use of antibiotics of the same class. For patients with a history of recent macrolide use,
the risks of macrolide resistance and the desire to preserve fluoroquinolones as a class makes ketolides
an attractive option in these patients. |
Emergence of Community-Acquired MRSA (CA-MRSA)
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In the last 18 months, CA-MRSA has started to appear throughout Ontario
with increasing frequency.
CA-MRSA strains are different from hospital-acquired strains. They occur
in adults and children without any exposure to hospitals or healthcare.
While they are sometimes associated with jails, intravenous drug use,
and living on the street, they also occur in children and adults without
these risk factors. Most infections with community acquired MRSA are skin infections.
The diagnosis of CA-MRSA should be considered in patients, particularly
children and young adults, who have large boils/carbuncles and those whose
cellulitis fails to respond to antibiotics.
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Laboratory Confirmed Influenza Illness (LCII)
| It is
important before the pandemic that we understand as much as possible
about the clinical features and complications of influenza, as well
as the impact of treatment with antivirals. For this reason
TIBDN has begun
population-based surveillance for laboratory-confirmed influenza
illness (LCII) resulting in hospital admission in residents of our
population area (metropolitan Toronto and the regional municipality
of Peel). A case of influenza requiring hospital admission is defined as a patient
whose illness requires hospitalization, and who has a positive antigen test
or a culture yielding influenza A. Clinical treatment and
outcomes of disease are shown in Table 2.
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These data illustrate that, despite that more than 40% of people in
Ontario receive influenza vaccine every year, influenza is still an
important disease. Current vaccines substantially reduce the mortality
associated with influenza (for adults over the age of 65, vaccination
is associated with 42% reduction in all cause mortality during influenza
season).
These data confirm data from randomized controlled trials that oseltamivir
therapy is associated with a very significant reduction in serious complications
and mortality due to influenza. Further, they suggest that if a patient is shedding
virus at admission (that is, has a positive rapid antigen test), treatment is
effective even if the patient has been symptomatic for more than 48 hours. During
influenza season, all patients who require admission and have symptoms of respiratory
infection should have a rapid test done for influenza, and should be treated with oseltamivir
(or zanamivir) if the test is positive.
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This website has been made possible through an unrestricted educational grant from
Pfizer Canada Inc. |
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