β-Lactamase-mediated ampicillin resistance rates for the 125 isolates were 16.4% for the respiratory isolates and 20% for the invasive isolates. These rates agree with previous reports of a decline in the prevalence of β-lactamase-producing NT Hi in recent years in both Canada and the United States (Zhanel et al., 2003; Heilmann et al., 2005). There was no statistical significance between the invasive and respiratory groups of NT Hi see more in the prevalence
of β-lactamase-mediated ampicillin resistance (P≥0.05 by χ2). However, significantly more invasive isolates (15% or 26.8%) than respiratory isolates (5% or 10.9%) were found to show decreased susceptibility towards ampicillin (P≤0.05 by χ2), possibly indicating a chromosomal-mediated ampicillin resistance mechanism that AZD3965 involves amino acid substitutions in the penicillin-binding protein 3 (PBP3) (Ubukata et al., 2001). Indeed, we have recently reported that Canadian β-lactamase-negative Hi showing decreased susceptibility towards ampicillin have significant mutations in their PBP3 (Shuel & Tsang, 2009). Further analysis in the future should monitor for this stepwise increase in their resistance to ampicillin. Of the 70 invasive Hi disease cases due to NT strains, 20 (or 28.6%) were in those 61–80 years of age and another 10 (14.3%) were in those 41–60 years of age. COPD is a common
morbidity, especially in the elderly (Murray & Lopez, 1997), and in the United States, 500 000 hospitalizations annually have been related to infections or acute exacerbations in patients with COPD (Snow et al., 2001). Because Hi, particularly the
NT strains, are common causes of acute exacerbations of chronic bronchitis in COPD patients (Sethi & Murphy, 2001), whether the high prevalence of NT Hi causing invasive diseases in those aged 41–80 in this study may be related to infections in COPD patients is worth examining in more detail. However, our present retrospective study did not allow us to look into this further without first obtaining ethics approval for reviewing patients’ medical history and coordination with Florfenicol individual hospital’s medical staff. Besides COPD, elderly patients (in the 61–80-year-old age group) are more likely to have other medical conditions such as diabetes, decreased immune functions, etc., which may predispose them to invasive infections by common respiratory bacteria such as NT Hi. One limitation of our study is the retrospective nature, which resulted in the lack of clinical correlations with the types of strains identified among the invasive and the respiratory isolates. Because of this lack of clinical data, it is not possible to identify whether any of the genotypes among the invasive isolates are genuinely virulent in causing disease in immunocompetent individuals.