Antimicrobial resistance
surveillance in Ireland
Results of invasive
Staphylococcus aureus infection
(blood) surveillance (2009Q1-4)
**** Data as of 14/04/2010 ****
Ireland is a member of the European Antimicrobial Resistance
Surveillance System (EARSS)
EARSS S. aureus:
Objective and case definition
Objective:

To determine the proportions of S. aureus isolates from
blood that are resistant to meticillin
Case definition:

EARSS collects data on the first invasive isolate (from
blood only) of S. aureus per patient per quarter
Caveats in interpreting EARSS data

Care must be exercised when interpreting the raw
figures, i.e. increases in numbers of isolates, as the
numbers of laboratories reporting to EARSS has
increased over the years

EARSS 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 EARSS in Ireland, including quarterly and annual
reports, plus reference/ resource material on the
individual pathogens under surveillance, see:
http://www.ndsc.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), 1999-2009Q1-4*
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
44
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
44
44
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)
* Data for 2009 provisional up to the end of Q4
S. aureus/MRSA bacteraemia trends,
1999-2009Q1-4*
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
* Data for 2009 provisional up to the end of Q4
Number of laboratories participating by year-end and quarter are indicated above the bars
%MRSA
1000
S. aureus/MRSA bacteraemia trends by quarter,
2002-2009Q1-4*
450
23
28
41
42
42
44
43
55%
44
50%
350
45%
300
250
40%
200
35%
150
30%
100
25%
50
20%
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
0
Total S.aureus
Quarter
MRSA
%MRSA
* Data for 2009 provisional up to the end of Q4;
Number of laboratories participating by year-end indicated above the Q4 bars
%MRSA
Number of isolates
400
S. aureus/MRSA bacteraemia trends,
2002-2009Q1-4*: 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
* Data for 2009 provisional up to the end of Q4;
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, 2009Q1-4
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, 2009Q1-4 (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,
2009Q1-4
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
4
65
18
7
177
49
5
120
30
6
187
76
48
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, 2009Q1-4
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
Rates of S. aureus bacteraemia isolates by
Hospital Network*, 2009Q1-4 (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, 2009Q1-4 (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, 2009Q1-4 (n=903)
Susceptibility data for S. aureus bacteraemia
isolates, 2009Q1-4 (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, 2009Q1-4 (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, 2009Q1-4 (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, 2009Q1-4 (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^, 1999-2009Q1-4
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; * 2009 data are provisional
Trends in proportion of fusidic acid resistance
among MRSA isolates^, 1999-2009Q1-4
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; * 2009 data are provisional
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,
2004-2009Q1-4
Year
2004
2005
2006
2007
2008
2009Q1-4
No. hospitals*
(Total hospitals)
57 (58)
57 (58)
53 (53)
52 (52)
50 (51)
48 (48)
Bed Days
Total
Used**
S.aureus
3,728,566
1282
3,792,972
1367
3,722,832
1353
3,747,184
1339
3,693,026
1259
3,685,647
1253
MRSA
545
577
572
526
425
350
%MRSA
42.5%
42.2%
42.3%
39.3%
33.8%
27.9%
MRSA
rate***
0.15
0.15
0.15
0.14
0.12
0.09
* Acute public hospitals only
** Bed days used (BDU) calculated from Acute Public Hospital Activity data for acute
public hospitals participating in EARSS
*** Per 1,000 bed days used
Vancomycin-Intermediate S. aureus (VISA)
reports from EARSS in 2009*
In 2008, 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 2008
90
80
Number of isolates
70
60
50
40
30
20
10
0
Age Group
MRSA
MSSA
Age-specific incidence rates of MRSA
and MSSA bacteraemia in 2008
250
200
ASIR
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 2008
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 2008
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 2008
60
Number of isolates
50
40
30
20
10
0
Age Group
female
male
Age and sex-specific incidence rates of
MSSA bacteraemia in 2008
200
180
160
140
ASIR
120
100
80
60
40
20
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 2008
MRSA
MSSA
SAU
n
435
854
1289
n with age
434
852
1286
66.5y
52.7y
57.4y
72y (70-74y)
59y (57-61y)
64y (62-66y)
Mode
78y
0y
0y
Range
0-96y
0-97y
0-97y
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 2008
MRSA
MSSA
Total
>=65y
290
337
627
<65y
144
515
659
Total
434
852
1286
Relative risk (RR)
=2.116671
(347/669)/(190/724)
= 2.12 (95% CI: 1.79-2.50)
Chi-squared
85.9
P-value
<0.0001
In patients with laboratory-confirmed S. aureus bacteraemia in 2008, the
probability that the infecting organism was MRSA as compared to MSSA was
over 2-times greater in patients aged ≥65years than in those aged <65 years
Sex distribution of patients with S. aureus
(MRSA and MSSA) bacteraemia in 2008
MRSA
MSSA
SAU
No. male
260
535
795
%male
40.1
62.7
61.8
No. female
174
318
492
%female
59.9
37.3
38.2
m/f ratio
1.49
1.68
1.62
z-test
4.21
7.68
8.69
<0.0001
<0.0001
<0.0001
P-value
In patients with laboratory-confirmed S. aureus bacteraemia in 2008, males were
approximately 1.6-times more likely to get an infection (1.5-times for MRSA and
1.7-times for MSSA) than females. These findings were significant (P<0.0001)
Distribution of MRSA in EARSS countries
in 2008
Map downloaded from http://www.rivm.nl/earss/database/ on 24/08/2009
Distribution of MRSA in EARSS countries
in 2007
Map downloaded from http://www.rivm.nl/earss/database/ on 26/08/2008
Distribution of MRSA in EARSS countries
in 2006
Map downloaded from http://www.rivm.nl/earss/database/ on 22/08/2007