Blot_edit.qxp 23/1/08 12:31 pm Page 108
Bacterial Infections
micro-organisms isolated in respiratory samples must be isolated in has been associated with a higher likelihood of associated bacteraemia.
blood cultures, whereas all isolates in blood cultures are required to In the Agbaht study, multivariate analysis identified MRSA involvement
grow in simultaneously obtained respiratory samples. in VAP as an independent predictor of bacteraemia.
Incidence and Risk Factors The propensity of S. aureus to cause bacteraemia is well known and has
In contrast with the extensive literature on bacteraemic pneumococcal been confirmed by in vitro studies, indicating that this pathogen is more
pneumonia, there have been only very few studies on the topic of adherent than other micro-organisms.
28,29
This phenomenon has been
nosocomial bacteraemic pneumonia. Although several studies have attributed to the interaction of plasma fibrinogen with the fibrinogen-
provided data on the epidemiology of nosocomial bacteraemic binding receptor (the clumping factor) found on S. aureus.
30
Strains
pneumonia,
21,22
only one study was specifically conducted to explore the carrying the clumping factor are known to cause more invasive disease.
31
differences compared with non-bacteraemic episodes.
23
As a
consequence, most of our knowledge is derived from series exclusively As fibrinogen is an acute-phase reactant that is frequently elevated in
containing bacteraemic pneumonia patients. critically ill patients, it has been proposed that increased levels of this
molecule may potentially increase its adsorption onto the endothelial
In a seven-year study of bacteraemic nosocomial pneumonia in surface in susceptible patients, thereby allowing more S. aureus to
both ICU patients and patients outside the ICU, Taylor et al. found adhere through the fibrinogen receptor.
that 8.4% of all bloodstream infections resulted from pneumonia as the
primary source of infection.
21
However, in a retrospective analysis of While the strong invasive potential of S. aureus can be reasonably
explained, it remains unclear why MRSA seems to be more prone
to causing systemic breakthrough. Differences in virulence between
Although several studies have provided S. aureus isolates are described, but this is more likely to be associated
data on the epidemiology of nosocomial
with particular strains than with methicillin resistance.
32
Alternatively,
delayed bacterial eradication of MRSA due to suboptimal tissue
bacteraemic pneumonia, only one
penetration of glycopeptides – as opposed to penicillin – may be a
study was specifically conducted to
significant factor.
explore the differences compared with
Clinical Impact
non-bacteraemic episodes.
Bacteraemic VAP is associated with high crude mortality. Depuydt et
al. described an in-hospital fatality rate of nearly 60%.
25
Similarly,
Bryan et al. observed a crude hospital mortality of 57%.
22
In the series
108 episodes of nosocomial pneumococcal bacteraemia, pneumonia by Taylor et al., one-week mortality was 21% – and 45% in the
was the port of entry in 70%.
24
Only one study addressed the subgroup with P. aeruginosa bacteraemia – but this series also
prevalence of bacteraemia in VAP: in a series of 223 episodes included non-VAP.
21
However, these data do not resolve the issue of
of VAP, bacteraemia occurred in 17.6%.
23
In this study by Agbaht et al., whether bacteraemic VAP is associated with higher mortality
patients with bacteraemia were older and had more frequent previous compared with non-bacteraemic VAP. Again, as far as we know this
hospitalisations than non-bacteraemic cases, although co-morbidity and has been addressed only in the study by Agbaht et al.
23
severity of underlying critical illness were similar in both groups.
Bacteraemic VAP episodes generally occurred later in the ICU course In a cohort of 35 bacteraemic and 170 non-bacteraemic VAP patients,
than non-bacteraemic VAP: 48.6% of bacteraemic VAP episodes were the authors observed a significantly higher mortality in bacteraemic
late–late in onset compared with 26.8% in the non-bacteraemic group patients (40 versus 21.4%). In multivariate analysis the relationship
(p=0.02). In a cohort study by Depuydt et al., 69% of bacteraemic
nosocomial pneumonia episodes occurred after seven days in the ICU.
25
The propensity of Staphylococcus
Aetiology
aureus to cause bacteraemia is well
As bacteraemic VAP tends to occur later in the course of the ICU stay in
critically ill patients, microbial aetiology is biased towards that of
known and has been confirmed by
late-onset VAP. Although S. pneumoniae has been shown to be an
in vitro studies, indicating that this
important pathogen causing nosocomial bacteraemia,
24,26
often
multidrug-resistant pathogens are involved, such as methicillin-resistant
pathogen is more adherent than
Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and other
other micro-organisms.
non-fermenting Gram-negative bacilli such as Acinetobacter baumannii.
In the study by Agbaht et al., P. aeruginosa was responsible for almost
20% of the cases of bacteraemic VAP versus 13% in non-bacteraemic between bacteraemic VAP and worse outcome was confirmed after
VAP.
23
Depuydt et al. found P. aeruginosa in approximately 20% of adjustment for potential confounders such as microbial aetiology and
bacteraemic pneumonia.
9,25
In a smaller series of nosocomial pneumonia severity of underlying critical illness. Given the imbalance in microbial
caused by multidrug-resistant Acinetobacter, Husni et al. found 50% of aetiology – in particular MRSA prevalence – between bacteraemic and
the cases to be bacteraemic.
27
S. aureus is frequently encountered in non-bacteraemic patients, the investigators additionally matched 32
bacteraemic VAP due to its invasive potential, and methicillin resistance bacteraemic cases with 57 non-bacteraemic control subjects for microbial
108 EUROPEAN INFECTIOUS DISEASE 2007
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130