Antimicrobial resistance
surveillance in Ireland
Results of invasive
Staphylococcus aureus infection
(blood) surveillance, 2009
**** Data as of 01/12/2010 ****
Ireland is a member of the European Antimicrobial Resistance
Surveillance Network (EARS-Net)
EARS-Net S. aureus:
Objective and case definition
Objective:

To determine the proportions of S. aureus isolates from
blood that are resistant to meticillin
Case definition:

EARS-Net collects data on the first invasive isolate
(from blood only) of S. aureus per patient per quarter
Caveats in interpreting EARS-Net data

Care must be exercised when interpreting the raw
figures, i.e. increases in numbers of isolates, as the
numbers of laboratories reporting to EARS-Net has
increased over the years

EARS-Net data does not distinguish clinically significant
isolates from contaminants

If MRSA is isolated subsequent to MSSA within the
same quarter, then that isolate is not counted (and
similarly if MSSA is isolated subsequent to MSSA)
[similarly for other pathogen-antibiotic resistance
combinations]
For further information on antimicrobial resistance
and EARS-Net in Ireland, including quarterly and
annual reports, plus reference/resource material on
the individual pathogens under surveillance, see:
http://www.hpsc.ie/hpsc/AZ/MicrobiologyAntimicrobialResistance/EuropeanAntimic
robialResistanceSurveillanceSystemEARSS/
Antibiotic codes and abbreviations:
CIP, Ciprofloxacin
FUS, Fusidic Acid
LIN, Lincomycin
MET, Meticillin
OXA, Oxacillin
RIF, Rifampicin
TEI, Teicoplanin
ERY, Erythromycin
GEN, Gentamicin
LNZ, Linezolid
MUP, Mupirocin
PEN, Penicillin
TCY, Tetracycline
VAN,Vancomycin
SAU, Staphylococcus aureus
MRSA, Meticillin-Resistant S. aureus
MSSA, Meticillin-Susceptible S. aureus
VISA,Vancomycin-Intermediate S. aureus
Numbers and proportions of S. aureus/MRSA
from bacteraemia with 95% confidence
Intervals (CI), 1999-2009
Time
period
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Number
of labs
11
18
20
23
28
41
42
42
44
43
43
Number
of S. aureus
510
639
816
1042
1140
1323
1424
1412
1393
1303
1309
Number
of MRSA
198
249
337
445
480
553
592
592
536
439
355
%MRSA
(95%CI)
38.8 (34.6-43.1)
39.0 (35.2-42.7)
41.3 (37.9-44.7)
42.7 (39.7-45.7)
42.1 (39.2-45.0)
41.8 (39.1-44.5)
41.6 (39.0-44.1)
41.9 (39.4-44.5)
38.5 (35.9-41.0)
33.7 (31.1-36.3)
27.1 (24.7-29.5)
2009Q1
2009Q2
2009Q3
2009Q4
44
44
43
43
343
328
336
302
103
92
87
73
30.0 (25.2-34.9)
28.0 (23.2-32.9)
25.9 (21.2-30.6)
24.2 (19.3-29.0)
S. aureus/MRSA bacteraemia trends,
1999-2009
1600
11 18 20
23
28
41
42
42
44 43
44
44 44
44 44
1400
Number of isolates
1200
50%
40%
30%
800
600
20%
400
10%
200
0
0%
Time period
Total S.aureus
MRSA
%MRSA
Number of laboratories participating by year-end and quarter are indicated above the bars
%MRSA
1000
Q1 2002
Q2 2002
Q3 2002
Q4 2002
Q1 2003
Q2 2003
Q3 2003
Q4 2003
Q1 2004
Q2 2004
Q3 2004
Q4 2004
Q1 2005
Q2 2005
Q3 2005
Q4 2005
Q1 2006
Q2 2006
Q3 2006
Q4 2006
Q1 2007
Q2 2007
Q3 2007
Q4 2007
Q1 2008
Q2 2008
Q3 2008
Q4 2008
Q1 2009
Q2 2009
Q3 2009
Q4 2009
Number of isolates
450
400
23
28
41
Total S.aureus
42
42
Quarter
MRSA
44
43
300
250
40%
200
35%
150
30%
100
50
25%
0
20%
%MRSA
Number of laboratories participating by year-end indicated above the Q4 bars
%MRSA
S. aureus/MRSA bacteraemia trends by quarter,
2002-2009
55%
44
50%
350
45%
S. aureus/MRSA bacteraemia trends,
2002-2009: 4-quarterly moving average
400
23
28
41
42
55%
42
44
43
44
50%
300
45%
40%
200
35%
150
30%
100
50
25%
0
20%
4-Quarter period ending…..
Total S.aureus
MRSA
%MRSA
Number of laboratories participating by year-end indicated above the Q4 bars
%MRSA
250
Q4 2002
Q1 2003
Q2 2003
Q3 2003
Q4 2003
Q1 2004
Q2 2004
Q3 2004
Q4 2004
Q1 2005
Q2 2005
Q3 2005
Q4 2005
Q1 2006
Q2 2006
Q3 2006
Q4 2006
Q1 2007
Q2 2007
Q3 2007
Q4 2007
Q1 2008
Q2 2008
Q3 2008
Q4 2008
Q1 2009
Q2 2009
Q3 2009
Q4 2009
Number of isolates
350
Numbers of S. aureus bacteraemia isolates
and %MRSA by Hospital Network, 2009
NHO Hospital
Network
Dub/M
Dub-N
Dub-S
MW
NE
S
SE
W/NW
Other
Private
ROI TOTAL
Total
S.aureus
186
228
219
71
65
177
120
187
8
48
1309
MRSA
42
48
60
27
18
49
30
76
2
3
355
MSSA
144
180
159
44
47
128
90
111
6
45
954
%MRSA
22.6%
21.1%
27.4%
38.0%
27.7%
27.7%
25.0%
40.6%
25.0%
6.3%
27.1%
Dub/M, Dublin Midlands; Dub-N, Dublin North; Dub-S, Dublin South; MW, Mid Western; NE,
North Eastern; NW, North Western; S, Southern; SE South Eastern; W/NW, West/North Western
Proportion of S. aureus bacteraemia isolates
by Hospital Network, 2009 (n=1309)
80%
1200
70%
60%
1000
50%
800
40%
600
30%
400
20%
200
10%
0
0%
Dub/M Dub-N Dub-S MW
NE
S
SE
W/NW Other Private ROI
TOTAL
Hospital Network
Total S.aureus
%MRSA
%MRSA
Number of isolates
1400
Numbers of S. aureus bacteraemia isolates,
%MRSA and rates by Hospital Network, 2009
NHO Hospital
Network
Dub/M
Dub-N
Dub-S
MW
NE
S
SE
W/NW
ROI TOTAL
BDU 2009
543,541
607,701
633,185
245,202
239,488
472,762
371,601
572,167
3,685,647
No.
Total
Hospitals S.aureus MRSA
7
186
42
6
228
48
7
219
60
6
71
27
5
65
18
7
177
49
5
120
30
6
187
76
49
1253
350
MSSA
144
180
159
44
47
128
90
111
903
S. aureus MRSA
%MRSA
rate
rate
22.6%
0.34
0.08
21.1%
0.38
0.08
27.4%
0.35
0.09
38.0%
0.29
0.11
27.7%
0.27
0.08
27.7%
0.37
0.10
25.0%
0.32
0.08
40.6%
0.33
0.13
27.9%
0.34
0.09
Dub/M, Dublin Midlands; Dub-N, Dublin North; Dub-S, Dublin South; MW, Mid Western; NE,
North Eastern; NW, North Western; S, Southern; SE South Eastern; W/NW, West/North Western
MSSA
rate
0.26
0.30
0.25
0.18
0.20
0.27
0.24
0.19
0.25
Numbers, proportions and rates of MRSA
bacteraemia by hospital type, 2009
Hospital Type
Acute Public Hospitals
Tertiary/Specialist
Secondary
Primary
Obs/Gynae*
Paediatric*
Orthopaedic*
Other*
Total Acute
Number of
hospitals
Bed days
Total
used (BDU) S. aureus
Total
MRSA
%MRSA
MRSA rate/
1000 BDU
9
20
8
4
2
4
2
49
1,796,139
1,291,156
219,042
190,504
91,372
49,858
47,576
3,685,647
698
401
57
41
43
1
12
1253
201
129
14
1
2
0
3
350
28.8%
32.2%
24.6%
2.4%
4.7%
0.0%
25.0%
27.9%
0.11
0.10
0.06
0.01
0.02
0.00
0.06
0.09
Private/Non-Acute Public Hospitals
Private (General/Specialist)
Private (General/Specialist)^
Non-Acute/Community
3
9
***
120,315
**
**
17
31
8
2
1
2
11.8%
3.2%
0.0%
0.02
**
**
TOTAL
61
***
1309
355
27.1%
***
*Single speciality hospitals;
** Denominator data (BDU, Bed Days Used) not available;
*** Complete denominator data not available;
^ includes all private hospitals/quarters for which no activity data were available
Note: BDU provided by the Acute Services Team in the Business Intelligence Unit, Corporate Planning and Corporate
Performance (CPCP) section of the Health Service Executive for acute hospitals and directly from the infection
control/finance departments from private hospitals
Rates of S. aureus bacteraemia isolates by
Hospital Network*, 2009 (n=1253)
0.50
0.45
1200
Number of isolates
0.40
1000
0.35
0.30
800
0.25
600
0.20
0.15
400
0.10
200
0.05
0
0.00
Dub/M Dub-N
Dub-S
MW
NE
S
Hospital Network
Total S.aureus
* excludes private hospitals and other non-acute facilities
SAU rate
SE
W/NW
ROI
TOTAL
MSSA rate per 1,000 Bed Days Used
1400
Rates of MRSA bacteraemia isolates by
Hospital Network, 2009 (n=350)
0.18
0.16
1200
Number of isolates
0.14
1000
0.12
800
0.10
600
0.08
0.06
400
0.04
200
0.02
0
0.00
Dub/M
Dub-N
Dub-S
MW
NE
S
SE
Hospital Network
Total S.aureus
* excludes private hospitals and other non-acute facilities
MRSA rate
W/NW
ROI
TOTAL
MRSA rate per 1,000 Bed Days Used
1400
1400
0.40
1200
0.35
0.30
1000
0.25
800
0.20
600
0.15
400
0.10
200
0.05
0
0.00
Dub/M
Dub-N
Dub-S
MW
NE
S
Hospital Network
Total S.aureus
* excludes private hospitals and other non-acute facilities
MSSA rate
SE
W/NW
ROI
TOTAL
MSSA rate per 1,000 Bed Days Used
Number of isolates
Rates of MSSA bacteraemia isolates by
Hospital Network, 2009 (n=903)
Susceptibility data for S. aureus bacteraemia
isolates, 2009 (n=1309)
1400
27.1%
30.1%
Number of isolates
1200
1000
0.1%
2.3%
19.2%
0.0%
27.6%
800
0.0%
2.0%
600
87.6%
400
200
1.9%
0.5%
0.0%
3.5%
0
Antibiotic
Resistant
Susceptible
4.6%
Susceptibility data for MRSA bacteraemia
isolates, 2009 (n=355)
400
100.0%
Number of isolates
0.0%
92.5%
1.8%
200
5.1%
150
98.3%
9.5%
100
50
0.0%
72.6%
38.1%
300
250
1.1%
5.3% 0.0%
350
10.0%
0.0%
0
Antibiotic
Resistant
Susceptible
Susceptibility data for MSSA bacteraemia
isolates, 2009 (n=954)
1000
0.0%
15.7%
900
12.8%
Number of isolates
800
700
0.1%
1.2%
0.0%
0.0%
5.8%
0.1%
600
1.9%
500
1.0% 84.5%
400
3.1%
300
200
100
1.2%
0.0%
0
Antibiotic
Resistant
Susceptible
Antibiogram results for MRSA isolates
referred to NMRSARL, 2009 (n=321)
100%
90%
80%
% of isolates
70%
60%
50%
40%
30%
20%
10%
0%
CHL
CIP
ERY
FUS
GEN
LIN
LNZ
MUP
RIF
TCY
Antibiotic
Resistant
Intermediate
Susceptible
Data provided by National MRSA Reference Laboratory, St James’s Hospital
TMP
VAN
Trends in proportion of gentamicin resistance
among MRSA isolates^, 1999-2009
600
11
18
20
23
28
41
42
42
44
43
44
60%
500
50%
400
40%
300
30%
200
%Gen-R MRSA
Number of isolates
70%
20%
100
10%
0
0%
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Total MRSA tested for GEN-R
GEN-R MRSA
%GEN-R MRSA
^ Data from National MRSA Reference Laboratory; Changes in the numbers of participating laboratories are
indicated above the bars
Trends in proportion of fusidic acid resistance
among MRSA isolates^, 1999-2009
600
11
18
20
23
28
41
42
42
44
43
44
60%
500
50%
400
40%
300
30%
200
%Fus-R MRSA
Number of isolates
70%
20%
100
10%
0
0%
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Total MRSA tested for FUS-R
FUS-R MRSA
%FUS-R MRSA
^ Data from National MRSA Reference Laboratory; Changes in the numbers of participating laboratories are
indicated above the bars
Statistical Process Charts




Assume proportion or rate stable over time (i.e. in control)
Mean calculated from data for quarters (data points) up to
the previous quarter, i.e. excluding latest quarter
Warning limits and action limits are equal to 2 and 3
Standard Deviations (SD), respectively
These are used to determine if:
◦ the trends in proportions or rates are behaving as expected, i.e.
the process is in control. The variation observed here is due to
chance (common cause or natural variation)
or
◦ the trends are not behaving as expected and something unusual
is happening, i.e. the process is out of control. The variation
observed here is unlikely to be due to chance alone. Special
circumstances are more likely to operate (special cause
variation) warranting further investigations
Statistical Process Charts
Special cause variation occurs if:
 One value above or below the action limits (±3SD)
 3 consecutive values between upper warning and action
limits (or lower limits)
 5 consecutive values in top or bottom 2/3 (between 1 and 3
SD, or -1 and -3 SD)
 13 consecutive values in top or bottom middle 1/3 (between
mean and 1 SD, or mean and -1 SD)
 8 consecutive values on the same side of the mean
 12 of 14 consecutive values on same side of the mean
 8 consecutive values either increasing or decreasing
 Cyclic or periodic behaviour
Statistical Process Chart
National MRSA proportions: P-Chart
55%
50%
Proportion
45%
40%
35%
30%
25%
Q1 2002
Q2 2002
Q3 2002
Q4 2002
Q1 2003
Q2 2003
Q3 2003
Q4 2003
Q1 2004
Q2 2004
Q3 2004
Q4 2004
Q1 2005
Q2 2005
Q3 2005
Q4 2005
Q1 2006
Q2 2006
Q3 2006
Q4 2006
Q1 2007
Q2 2007
Q3 2007
Q4 2007
Q1 2008
Q2 2008
Q3 2008
Q4 2008
Q1 2009
Q2 2009
Q3 2009
Q4 2009
20%
Quarter
%MRSA
Mean %MRSA
UWL
LWL
UAL
LAL
Mean proportion calculated from data for Q1 2002-Q3 2009;
UWL and LWL, Upper and Lower Warning Limits; UAL and LAL (±2 Standard Deviations), Upper and Lower
Action Limits (±3 Standard Deviations)
Statistical Process Chart
National MRSA rates: U-Chart
Rate per 1,000 Bed Days Used
0.25
0.20
0.15
0.10
0.05
0.00
MRSA rate
Mean rate
Quarter
UWL
LWL
UAL
LAL
Mean rate calculated from data for Q1 2004-Q3 2009;
UWL and LWL, Upper and Lower Warning Limits (±2 Standard Deviations); UAL and LAL, Upper and Lower
Action Limits (±3 Standard Deviations)
Statistical Process Charts
P-chart:
 The proportion of MRSA bacteraemia was above its upper control
limit in Q2 2002, Q2 2003 and Q3 2006 and below its lower
control limit for Q4 2007 and Q2 2008–Q4 2009. These indicate
that the process is out of control - if true, the former represents a
worsening situation and the latter an improving situation regarding
%MRSA
U-chart
 The rate of MRSA bacteraemia was above its upper control limit in
Q2 2005 and below its lower control limit for Q2 2008–Q4 2009,
(except for Q1 2008) indicating that out of control - if true, the
former represents a worsening situation and the latter an
improving situation regarding %MRSA
Worsening/improving situations warrant further investigation to
determine reasons why
Rates of S. aureus and MRSA bacteraemia,
2004-2009
Year
2004 4
2005 4
2006
2007
2008
2009
1 Acute
No. hospitals
Bed Days
Total
(Total hospitals)¹
Used²
S.aureus
57 (58)
57 (58)
56 (65)
54 (64)
52 (62)
53 (62)
3,728,566
3,792,972
3,893,386
3,981,774
3,882,298
3,875,733
1282
1367
1412
1393
1303
1309
MRSA
%MRSA
MRSA rate³
545
577
592
536
439
355
42.5%
42.2%
41.9%
38.5%
33.7%
27.1%
0.15
0.15
0.15
0.13
0.11
0.09
hospitals only (Total hospitals = Total acute hospitals in Ireland)
Bed Days Used (BDU) provided by the Acute Services Team in the Business Intelligence Unit,
Corporate Planning and Corporate Performance (CPCP) section of the Health Service Executive for
acute public hospitals and directly from the infection control/finance departments from acute private
hospitals
3 Per 1,000 BDU: for 2004 and 2005, rates calculated using data from acute public hospitals only; for the
period 2006-2009, rates calculated using data from all public and private acute hospitals for which both
numerator (MRSA isolates) and denominator ( BDU) data available
4 Data from acute public hospitals only
2
Vancomycin-Intermediate S. aureus (VISA)
reports from EARSS in 2009*
In 2009, no MRSA isolates with reduced susceptibility to vancomycin were
detected by the Etest macromethod
In 2006, two VISA isolates were detected, which were the first reports of
VISA from EARSS in Ireland:
• both were confirmed as VISA by CDC
• one was shown to be VISA and the other to be h-VISA by
population analysis profiling (PAP) studies
*Data from the National MRSA Reference Laboratory, where all EARSS MRSA isolates submitted by
participating laboratories are tested for reduced susceptibility to vancomycin
Age distribution of patients with MRSA and
MSSA bacteraemia in 2009
120
Number of isolates
100
80
60
40
20
0
Age Group
MRSA
MSSA
Age-specific incidence rates of MRSA
and MSSA bacteraemia in 2009
350
300
ASIR
250
200
150
100
50
0
MRSA
Age Group
MSSA
ASIR, Age-Specific Incidence Rate (per 100,000 population)
TOTAL
Age and sex distribution of patients with
MRSA bacteraemia in 2009
50
45
Number of isolates
40
35
30
25
20
15
10
5
0
Age Group
female
male
Age and sex-specific incidence rates of
MRSA bacteraemia in 2009
250
200
ASIR
150
100
50
0
Age Group
female
male
ASIR, Age-Specific Incidence Rate (per 100,000 population)
TOTAL
Age and sex distribution of patients with
MSSA bacteraemia in 2009
70
Number of isolates
60
50
40
30
20
10
0
Age Group
female
male
Age and sex-specific incidence rates of
MSSA bacteraemia in 2009
400
350
300
ASIR
250
200
150
100
50
0
Age Group
female
male
ASIR, Age-Specific Incidence Rate (per 100,000 population)
TOTAL
Mean, median, mode and range of ages of
patients with S. aureus (MRSA and MSSA)
bacteraemia in 2009
MRSA
MSSA
SAU
n
355
954
1309
n with age
355
954
1309
66.4y
54.6y
57.8y
72y (70-73y)
62y (60-64y)
65y (64-66y)
Mode
78y
0y
0y
Range
0-99y
0-99y
0-99y
Mean
Median
The difference in median ages for patients with MRSA and MSSA
bacteraemia is significant as the confidence intervals do not overlap
Relative risk of developing MRSA bacteraemia
associated with age in 2009
MRSA
MSSA
Total
>=65y
224
441
665
<65y
131
513
644
Total
355
954
1309
Relative risk (RR)
=1.655926
(347/669)/(190/724)
= 1.66 (95% CI: 1.37-2.00)
Chi-squared
29.5
P-value
<0.0001
In patients with laboratory-confirmed S. aureus bacteraemia in 2009, the
probability that the infecting organism was MRSA as compared to MSSA was
approximately1.7-times greater in patients aged ≥65years than in those aged
<65 years
Sex distribution of patients with S. aureus
(MRSA and MSSA) bacteraemia in 2009
MRSA
MSSA
SAU
No. male
239
606
845
%male
67.3
63.5
64.6
No. female
116
348
464
%female
32.7
36.5
35.4
m/f ratio
2.06
1.74
1.82
z-test
6.96
8.68
11.01
<0.0001
<0.0001
<0.0001
P-value
In patients with laboratory-confirmed S. aureus bacteraemia in 2009, males were
approximately 1.8-times more likely to get an infection (2.1-times for MRSA and
1.8-times for MSSA) than females. These findings were significant (P<0.0001)
Distribution of MRSA in EARSS/EARS-Net
countries in 2009
Map downloaded from:
http://ecdc.europa.eu/en/activities/surveillance/EARS-Net/Pages/Database.aspx on 20/12/2010
Distribution of MRSA in EARSS countries
in 2008
Map downloaded from http://www.rivm.nl/earss/database/ on 24/08/2009