Staphylococcus aureus bacteremia, Australia.

Staphylococcus aureus bacteremia (SAB) is common and increasing worldwide. A retrospective review was undertaken to quantify the number of cases, their place of acquisition, and the proportions caused by methicillin-resistant S. aureus (MRSA) in 17 hospitals in Australia. Of 3,192 episodes, 1,571 (49%) were community onset. MRSA caused 40% of hospital-onset episodes and 12% of community-onset episodes. The median rate of SAB was 1.48/1,000 admissions (range 0.61-3.24; median rate for hospital-onset SAB was 0.7/1,000 and for community onset 0.8/1,000 admissions). Using these rates, we estimate that [approximately equal to] 6,900 episodes of SAB occur annually in Australia (35/100,000 population). SAB is common, and a substantial proportion of cases may be preventable. The epidemiology is evolving, with >10% of community-onset SAB now caused by MRSA. This is an emerging infectious disease concern and is likely to impact on empiric antimicrobial drug prescribin in suspected cases of SAB.

**********

Bacteremia caused by Staphylococcus aureus continues to be a common problem worldwide. In the preantibiotic era, most cases occurred in young patients without underlying disease. The associated death rate was 82% (1). Even with antimicrobial drug treatment, death rates remain high; in a recent meta-analysis of 31 studies, estimates of death rates for methicillin-resistant strains (MRSA) varied from 0.0% to 83.3% (median 34.2%), while those for methicillin-sensitive strains (MSSA) varied from 3.6% to 51.7% (median 25.0%) (2). Many of these infections are healthcare associated and thus are potentially preventable.

Antimicrobial drug resistance in S. aureus arose early after the development of antimicrobial agents and continues to evolve. In Australia, hospital strains are frequently methicillin resistant and resistant to several other antimicrobial drugs (3). This resistance limits the choice of potentially efficacious agents and results in frequent use of glycopeptides, such as vancomycin. The reliance on vancomycin causes difficulties because vancomycin has been shown to be less effective than isoxazolyl penicillins (e.g., flucloxacillin) in treating severe infections caused by S. aureus (4,5). This may be 1 explanation for the higher death rate associated with bacteremia caused by MRSA, compared with that caused by MSSA (2,6). Although MRSA tends to be the bacterium discussed most often in relation to healthcare-associated infections, MSSA strains are responsible for the largest proportion of hospital-acquired infections (3).

S. aureus remains a common cause of bloodstream infections of community onset. Increasing numbers of these community-onset infections are being caused by MRSA. Some of these infections may be caused by hospital strains carried into the community by patients or healthcare workers, but others are caused by true community strains in patients who have had no recent healthcare contact (7-9). These strains have emerged in many countries, including Australia, New Zealand, the United States, Canada, France, Switzerland, Greece, Denmark, Finland, Scotland, and the Netherlands. They are susceptible to most or all non-[beta]-lactam antimicrobial drugs, are highly pyogenic, and are often associated with indigenous populations (10,11).

Although S. aureus is a well-known major cause of bacteremia, population-based estimates of its incidence are lacking. This study used hospital data to estimate the incidence of S. aureus bacteremia in Australia. In addition, we classified episodes on the basis of community or hospital onset and on the basis of methicillin susceptibility.

Methods

S. aureus bacteremia data were obtained from microbiology departments that prospectively collected information for >12 months on episodes of laboratory-confirmed bacteremia for the hospitals they serviced from January 1, 1999, to December 31, 2002. Information retrieved from existing databases included the total number of episodes of community- and hospital-onset bacteremia, the number of episodes of community- and hospital-onset MRSA and MS SA bacteremia, the total number of hospital separations (defined as completed hospital admissions), and the mean length of stay. Multiple positive blood cultures in the same patient within 14 days were considered a single episode. Episodes were considered to have a hospital onset when the first positive blood culture was collected >48 hours after admission to hospital. All other infections were designated community onset (for example, day-only dialysis related episodes were defined as community onset, as were infections with their onset in nursing homes). Organism identification and susceptibility testing were by standard methods. All these laboratories participate in external quality assurance programs as well as AGAR national surveys (3,12), which have quality control procedures to ensure these laboratories accurately detect methicillin resistance. Published data were used for the details on the number of hospital beds and separations for Australia and for the classification of different types of hospitals (13). The term separations, rather than admissions, is used in the published data because hospital abstracts for inpatient care are based on information gathered at the time of discharge. We have used the more commonly applied term of admissions, however, for these episodes.

In Australia, most healthcare-associated MRSA is caused by 1 clone defined by multilocus sequence type (ST) 239; this clone is characteristically resistant to multiple antimicrobial agents, including gentamicin (3,12). Most of the remaining healthcare-associated infections are caused by a recently introduced strain, ST22, which is indistinguishable from epidemic MRSA-15 in the United Kingdom. It is invariably resistant to ciprofloxacin (12). Thus, in Australia, MRSA that is acquired in the community and is sensitive to both eiprofloxacin and gentamicin is not likely to be associated with healthcare facility acquisition. We used this pattern as a surrogate marker for community acquisition of MRSA without healthcare-associated risk factors.

Results

We detected 12,771 bloodstream infections in the 17 hospitals participating in this study (12 principal referral metropolitan, 3 large metropolitan, 1 private hospital, and 1 medium-sized public hospital, and 1 private hospital with 2,013,534 total separations; Table 1). There were 3,192 episodes of S. aureus bacteremia identified (i.e., 25% of the total true bloodstream infections). The median rate of S. aureus bacteremia was higher in the principal referral metropolitan hospitals (1.59/1000 admissions) than in large metropolitan hospitals (1.3) or the private hospital (0.6). The range varied from 0.60 to 3.24 (Table 2). The median rate of community-onset bacteremia episodes was 0.80/1000 admissions (range 0.11-0.99). The median rate of hospital-onset bacteremia was 0.72 episodes/1,000 admissions (range 0.13-1.30). The median rate of hospital-onset MRSA episodes was 0.22/1,000 admissions (range 0-0.89). When expressed as MRSA episodes per 1,000 occupied bed days (OBDs), the rates varied from 0 to 0.30 with a median rate of 0.08. If day-only cases are removed from the denominator then the median rate was 0.10 per 1,000 OBDs (range 0-0.39).

Of these 3,192 SAB episodes, 1,621 (51%) were of hospital onset, and 1,571 (49%) had their onset in the community. Of those with a hospital onset, 40% were MRSA in comparison to 12% with a community onset. Of all MRSA bacteremia episodes, 23% had a community onset, and 77% had hospital onset. Of the 193 community-onset episodes of MRSA that occurred, only 47 (24%) had a sensitivity pattern (sensitive to gentamicin and ciprofloxacin) that suggests that they were community acquired.

When both MRSA and MSSA were considered, data were available for 560 community-onset SAB infections (but only from 4 hospitals). The proportions of these episodes that were noninpatient, healthcare-associated were 35%, 42%, 18% and 16%, respectively (from hospitals A, D, E, and N). In those hospitals, the percentage of S. aureus episodes that were healthcare associated overall (i.e., all hospital-onset cases and those community-onset cases associated with healthcare exposure) were 75%, 69%, 64%, and 36%, respectively.

Mortality data were available for 526 patients from 2 hospitals. At hospital E, the mortality rate at day 7 was 10% (27 of 267 patients). When a subgroup of these patients at hospital E (52 patients) was followed for a longer period (2001-2002), the mortality rate was 23% at 30 days and 35% at 6 months. For those 24 patients with a community-onset episode of bacteremia that was not healthcare associated, mortality rates were 6% at day 7, 17% at 1 month, and 21% at 6 months, respectively. At hospital H (259 patients), the mortality rate at 30 days was 19%. At hospital H, the mean length of stay for those with SAB was 25.6 days compared to 6.2 days in matched controls. The mean length of stay was longer for MRSA infections (39.2 days) than for MSSA infections (23.3 days).

The rates of S. aureus bacteremia in different hospital populations were used to estimate the incidence for Australia. Using our median bacteremia rate for S. aureus bacteremia in different types of public hospitals (1.27/1,000 admissions, range 0.68 3.24) and in private hospitals (0.6/1,000 admissions), we estimated [approximately equal to] 6,900 episodes per year nationally (range 3,826-20,658) or 35/100,000 per year (Tables 3 and 4). Some data are available from other countries for comparison; the lowest annual rates are in Northern Ireland (23/100,000) and the highest in the United States (56/100,000; Table 4). However only 2 countries, Denmark and England, appeared to have comprehensive collection systems, and their rates were 29/100,000 and 37/100,000, respectively (17,20,22).

Discussion

S. aureus bacteremia is very common. Approximately one fourth (26%) of all S. aureus bacteremia episodes were caused by MRSA, and, as expected, the onset of most of these episodes was in hospitals (77%). Notably, however, 12% of all community-onset S. aureus infections were MRSA, which was 23% of all MRSA bloodstream infection episodes. A recent study from the United States similarly showed that 15% of community-onset SAB episodes were MRSA (14). Most of the community-onset strains in our study were multiresistant or phenotypically consistent with UK EMRSA-15 (15) and thus most likely to have been acquired by patients who had previous hospital contact, with nursing home contact a major factor in at least 1 of the hospitals in this study (hospital G). However, approximately one fourth of these community-onset MRSA infections were caused by other phenotypes of non-multiresistant MRSA and thus more likely to be true community-acquired episodes of MRSA bacteremia. Severe cases of MRSA bacteremia not associated with prior healthcare contact have been reported previously in Australia (7,9,16).

Use of the >48 hours postadmission definition of hospital onset underestimates the number of episodes of bacteremia that are healthcare associated. Many patients with chronic conditions are now treated in the community or on a day-only basis. Vascular lines are increasingly used in the community and outpatient settings, providing a potential source of bacteremia. The collection of data on the true association of episodes of bacteremia to health care is time-consuming and was not done by most institutions participating in this study. However, 3 principal referral hospitals (hospitals A, D, and E) did collect these data for 971 episodes, and 64%-75% of their total S. aureus bacteremia episodes were healthcare associated Only 46%-61% of the episodes were acquired while the patient was an inpatient (i.e., >48 h in hospital). This finding means that in these larger hospitals approximately one third of healthcare-associated episodes were acquired by either outpatients or short-stay patients. These episodes are better defined as "noninpatient, healthcare-associated." In a recent study in the United States, 62% of their community-onset SAB infections were healthcare related (with intravenous [IV] catheters the most common clinically apparent site of infection) (14). On the basis of our data, we conclude that in Australia approximately two thirds of all SAB episodes were associated with healthcare or medical procedures (i.e., all hospital-onset and approximately one third of community-onset episodes). A similar situation is evident in Denmark (17), where in 2002, at least 59% of all S. aureus infections were associated with healthcare procedures. Clearly, substantial scope exists internationally for interventions in healthcare settings to decrease the numbers of these episodes (especially those related to IV catheters). Interventions to reduce S. aureus bacteremia need to target healthcare-associated infections in the broadest sense and include those following non-inpatient-related medical procedures.

Community-onset infections that have no healthcare association are also common and associated with a high death rate (17% and 19% at hospitals E and H at 1 month, respectively). How best to intervene to decrease these infections is difficult to determine. Vaccination is a possibility for the future; a recent trial of a conjugated capsular polysaccharide vaccine in renal dialysis patients estimated efficacy at [approximately equal to] 60% (18). However, vaccination for the general population is unlikely to be available soon. We should therefore concentrate on reducing the number of deaths from established infections. Because the mortality rate associated with community-acquired bacteremia increases with inadequate empiric therapy (19), all efforts should be made to promote compliance with published guidelines for treatment of severe staphylococcal sepsis, including adequate duration of therapy.

Available data suggest that staphylococcal bacteremia is a major global health problem. The median death rate for MSSA infections is 25%, and for MRSA infections, 34% (20). Thus, >1,700 deaths in Australia are likely associated with S. aureus bacteremia per year (assuming 6,900 episodes or a bacteremia rate of 35/100,000/year). This estimate of the rate of SAB is similar to England (20,22) but much lower than in the United States on the basis of the rate derived from the figures available in the only comparative study (55/100,000) (14). Our estimated rate in Australia is higher than that in Denmark (17,21). It is also higher that those reported from Wales (22) and Ireland (23) (Table 4); however, all episodes from these last 2 countries likely were not reported in their voluntary reporting schemes. England changed recently from a similar voluntary reporting scheme to a compulsory scheme, and the numbers of reported episodes increased by almost 50% (24).

The rate of MRSA bacteremia in England was higher per 1,000 OBDs than in our figures from Australia (0.17 compared to 0.10 episodes per 1,000 OBDs, respectively). MRSA was a substantial cause of episodes of SAB in this study (26%). However, this percentage was lower than that seen in most other countries (e.g., Wales, 47%; Table 4) with the notable exception of Denmark (0.6% in 2002) (17).

We may have overestimated the number of cases of bacteremia occurring in Australia because of the overrepresentation of larger hospitals in our survey. However, these hospitals participated because they had in place surveillance systems for measuring all episodes of bacteremia. The rates of SAB may have been relatively lower in these hospitals because they were also more likely than were hospitals without surveillance systems to have infection control programs in place to try to decrease the numbers of these episodes. If systems were in place that better captured and reported on all bacteremia episodes in well-defined populations (e.g., all of Australia or a state), then this would give a more accurate rate. Such systems appear only to be in place in Denmark and England (17,21,24). Currently, no such systems are operating in Australia. Limited data are available from a voluntary surveillance system in Victoria (25) that captures an estimated two thirds of bacteremic episodes that occur in that state. The extrapolated rate (27 episodes/100,000 persons/year; Table 4) was slightly lower than what we estimated for all of Australia in this study.

Substantial illness and increased medical costs are also associated with staphylococcal bacteremia. S. aureus bacteremia is often related to serious infections, including endocarditis, osteomyelitis, and septic arthritis. It frequently results in prolonged hospital admission and increased costs. In hospital H, the average length of stay for patients with S. aureus bacteremia was 26.5 days. In South Australia, the estimated additional cost of each episode of hospital-acquired S. aureus infection was $22,000 in 1998 (26). Nationally, these South Australian costs translate to additional hospital costs of [approximately equal to] $150 million dollars ($22,000 x 6,900 episodes).

Treatment of S. aureus infections is complicated by the high prevalence of antimicrobial drug resistance. Although this has long been the case with multiresistant strains of MRSA in hospitals, the spread of hospital strains into the community, as well as the emergence of unique strains of MRSA unrelated to health care, have made this an issue of general importance. At least 3 community strains of MRSA are currently circulating in Australia (10,27,28). Two of these 3 community strains carry the gene for Panton-Valentine leukocidin, which is associated with subcutaneous abscess formation and necrotizing pneumonia. A number of reports have already highlighted the clinical impact of infection due to these strains (9,28-30). Surveillance data show that their prevalence is increasing in our capital cities, but the situation in rural Australia is not well documented (3). This increase will inevitably affect guidelines for empirical antimicrobial drug prescribing for staphylococcal infections and for patients in the community with suspected SAB. Further surveillance of staphylococcal infections, including bacteremia, is warranted to guide recommendations for empirical therapy and infection control interventions.

Table 1. Bacteremia ei isodes at individual hospitals *

                                          Hospital

                                A            B              C

Classification ([dagger])       a            a              a
Beds                           723          587            551
Years studied               4 ([double   4 ([double   3 ([section])
                             dagger])     dagger])
Admissions over              256,251      203,130        150,502
  study period
Admissions >24 h              66,035       76,147        49,501
  over study period
Mean length of stay            3.85         3.48          3.84
  (day cases included)
OBDs (including day          986,566      706,892        577,928
  only patients)
OBDs (excluding day          796,350      579,909        476,927
  only patients)
Total S. aureus                331          365            333
  bacteremia
Total BSIs over study         1,531        1,172          1,294
  period (all orgs)
Total BSI rate per             5.97         5.76          8.60
  hosp admissions
  (X1,000)

                                          Hospital

                                D            E              F

Classification ([dagger])       a            a              a
Beds                           525          504            468
Years studied               4 ([double   4 ([double   3 ([section])
                             dagger])     dagger])
Admissions over              204,116      194,246        132,781
  study period
Admissions >24 h             102,361       60,498        42,515
  over study period
Mean length of stay            3.60         3.43          3.80
  (day cases included)
OBDs (including day          781,235      666,264        504,568
  only patients)
OBDs (excluding day          679,481      532,516        414,302
  only patients)
Total S. aureus                373          267            107
  bacteremia
Total BSIs over study         1,546         196            605
  period (all orgs)
Total BSI rate per             7.57         6.67          4.50
  hosp admissions
  (X1,000)
                                          Hospital

                                G            H              I

Classification ([dagger])       a            a              a
Beds                           455          394            391
Years studied               4 ([double   4 ([double   2 ([paragraph])
                             dagger])     dagger])
Admissions over              185,680      175,583         67,855
  study period
Admissions >24 h              39,758       44,502         47,406
  over study period
Mean length of stay            3.61         3.32           4.25
  (day cases included)
OBDs (including day          670,305      582,936        288,384
  only patients)
OBDs (excluding day          524,383      451,855        267,935
  only patients)
Total S. aureus                426          259            115
  bacteremia
Total BSIs over study         1,689        1,120           472
  period (all orgs)
Total BSI rate per             9.01         6.38           6.95
  hosp admissions
  (X1,000)

                                            Hospital

                                J               K              L

Classification ([dagger])       a               a              a
Beds                           368             297            276
Years studied               4 ([double   2 ([paragraph])   4 ([double
                             dagger])                       dagger])
Admissions over              104,534         58,549          92,114
  study period
Admissions >24 h              50,018         25,617          36,322
  over study period
Mean length of stay            4.10           4.49            3.06
  (day cases included)
OBDs (including day          428,589         262,592        281,869
  only patients)
OBDs (excluding day          374,073         229,660        226,077
  only patients)
Total S. aureus                155             123             72
  bacteremia
Total BSIs over study          653             338            351
  period (all orgs)
Total BSI rate per             6.25           5.77            3.81
  hosp admissions
  (X1,000)

                                          Hospital

                                M            N            O

Classification ([dagger])       b            b            b
Beds                           199          170          162
Years studied               4 ([double   4 ([double   4 ([double
                             dagger])     dagger])     dagger])
Admissions over               64,311       41,690       48,900
  study period
Admissions >24 h              31,259       10,556       31,681
  over study period
Mean length of stay            3.37         5.4          3.60
  (day cases included)
OBDs (including day          216,728      225,126      176,040
  only patients)
OBDs (excluding day          183,676      192,874      158,821
  only patients)
Total S. aureus                 44          135           62
  bacteremia
Total BSIs over study          282          881          274
  period (all orgs)
Total BSI rate per             4.39        21.13         5.60
  hosp admissions
  (X1,000)

                                          Hospital

                                P            Q          Total

Classification ([dagger])       c            d           --
Beds                            72           52         6,194
Years studied               4 ([double   4 ([double      --
                             dagger])     dagger])
Admissions over               18,223       15,069     2,013,534
  study period
Admissions >24 h              13,055       2,894       730,125
  over study period
Mean length of stay            5.10         2.88         --
  (day cases included)
OBDs (including day           92,937       43,399     7,491,240
  only patients)
OBDs (excluding day           87,769       31,224     6,207,832
  only patients)
Total S. aureus                 11           14         3,192
  bacteremia
Total BSIs over study           67           63        12,771
  period (all orgs)
Total BSI rate per             3.68         4.18         --
  hosp admissions
  (X1,000)

* MSSA, methicillin-susceptible Staphylococcus aureus; MRSA,
methicillin-resistant S. aureus; OBDs, occupied bed days; BSI,
bloodstream infection; orgs, microorganisms.

([dagger]) Hospital classification: a, principal referral: metropolitan
(>20,000 acute weighted separations per year) and rural (>16,000 acute
weighted separations); b, large metropolitan (>10,000 acute weighted
separations); c, private hospital; d, medium sized (metropolitan and
rural 2,000 acute or acute weighted to 5,000 acute weighted
separations).

([double dagger]) 1999-2002.

([section]) 1999-2001.

([paragraph] 1999-2000.

Table 2. Staphylococcus aureus bacteremia at individual hospitals *

                       Rate ([dagger])

                       Community-   Hospital-onset
                         onset        S. aureus
           Incidence   infections     infection
           ([double     ([double       ([double
Hospital   dagger])     dagger])       dagger])

A            1.29         0.51           0.78
B            1.80         0.74           1.05
C            2.21         0.94           1.27
D            1.83         0.99           0.84
E            1.37         0.66           0.72
F            0.80         0.35           0.46
G            2.29         0.99           1.30
H            1.48         0.83           0.65
I            1.69         0.77           0.93
J            1.48         0.88           0.60
K            2.10         1.06           1.04
L            0.78         0.58           0.21
M            0.68         0.48           0.20
N            3.24         2.40           0.84
O            1.27         0.80           0.47
P            0.60         0.11           0.49
Q            0.93         0.80           0.13
Total        1.59         0.78           0.81

                    Rate ([dagger])

           Hospital-   Hospital-
             onset       onset
             MSSA        MRSA          SAB
           ([double    ([double      sepsis
Hospital   dagger])    dagger])    ([section])

A            0.54        0.24         0.34
B            0.58        0.48         0.52
C            0.74        0.53         0.58
D            0.64        0.20         0.48
E            0.46        0.26         0.40
F            0.42        0.04         0.21
G            0.41        0.89         0.64
H            0.55        0.10         0.44
I            0.49        0.44         0.40
J            0.25        0.35         0.35
K            0.59        0.44         0.47
L            0.10        0.11         0.26
M            0.08        0.12         0.20
N            0.62        0.22         0.60
O            0.41        0.06         0.35
P            0.44        0.05         0.12
Q            0.13        0.00         0.32
Total        0.49        0.32         0.43

                Rate ([dagger])

             MRSA SAB       MRSA SAB
           ([section])    ([section])
           (including 1   (excluding 1
Hospital    day only)      day only)

A              0.08           0.10
B              0.17           0.21
C              0.18           0.22
D              0.08           0.09
E              0.09           0.11
F              0.01           0.01
G              0.30           0.39
H              0.05           0.06
I              0.14           0.15
J              0.15           0.02
K              0.13           0.15
L              0.05           0.06
M              0.05           0.05
N              0.06           0.07
O              0.02           0.03
P              0.01           0.01
Q              0.00           0.00
Total          0.11           0.13

* MSSA, methicillin-susceptible S. aureus; MRSA, methicillin-resistant
S. aureus; SAB, S. aureus bacteremia.

([dagger]) Data for these calculations presented in expanded online
table, available at http://vpAw.cdc.gov/ncidod/eid/vol11no04/
04-0772.htm#table2

([double dagger]) Per hospital admission (x1,000).

([section]) Per occupied bed days (x1,000).

Table 3. Estimated numbers of Staphylococcus aureus bacteremia in
Australia *

                                       Total hospitals ([dagger])

Published data for Australia         Acute public
2001-2002 (13)                     ([double dagger])       Private

No. hospitals                             724          537 ([section])
No. beds                                49,004             27,407
Total admissions (x1,000)                3,950              2,426
Same day separations (x1,000)            1,886              1,453
Average length of stay                    4.1                2.9
S. aureus BSI episodes;
    (calculated rates from data
    in this study)
  S. aureus BSI rate/1,000             0.68-3.24             0.6
    admissions
  Estimated episodes/y               2,370-12,798           1,456
  Median rate/1,000 admissions           1.37                0.6
  Estimated episodes/y (based on         5,412              1,456
    median)
Hospital-onset MSSA
  Rate/1000 admissions                 0.08-0.74            0.44
  Estimated episodes/y                 316-2,923            1 067
  Median rate/1,000 admissions           0.47               0.44
  Estimated episodes/y (based on         1,769              1,067
    median)
Hospital-onset MRSA
  Rate/1,000 admissions                0.05-0-89            0.05
  Estimated episodes/y                 198-3,516             121
  Median rate/1,000 admissions           0.25               0.05
  Estimate episodes/y (based on           868                121
    median)

                                   Total hospitals
                                   ([dagger])

Published data for Australia        Australia-
2001-2002 (13)                         wide

No. hospitals                         1,306
No. beds                              75,516
Total admissions (x1,000)             6,376
Same day separations (x1,000)           --
Average length of stay                 3.5
S. aureus BSI episodes;
    (calculated rates from data
    in this study)
  S. aureus BSI rate/1,000           0.6-3.24
    admissions
  Estimated episodes/y             3,826-20,658
  Median rate/1,000 admissions          NA
  Estimated episodes/y (based on      6,867
    median)
Hospital-onset MSSA
  Rate/1000 admissions              0.10-0.97
  Estimated episodes/y              638-4,718
  Median rate/1,000 admissions          NA
  Estimated episodes/y (based on      2,836
    median)
Hospital-onset MRSA
  Rate/1,000 admissions             0.05-0.89
  Estimated episodes/y              255-5,675
  Median rate/1,000 admissions          NA
  Estimate episodes/y (based on       1,015
    median)

* BSI, bloodstream infection; MSSA, methicillin-sensitive S. aureus;
MRSA, methicillin-resistant S. aureus; NA, not applicable.

([dagger]) For full details for individual hospitals in this study
and hospital grouping, see Table 3 at http://www.cdc.gov/ncidod/eid/
vol11no04/04-0772.htm#table3

([double dagger]) Acute public hospitals exclude psychiatric hospitals.

([section]) Of private hospitals, 246 were day only, 314 others had
admissions for >24 h.

Table 4. International rates and numbers of Staphylococcus
aureus bacteremia (SAB) *

Country                              Y       Population   SAB/y

Australia
  Present report                 1998-2002   19,500,000   6,900
  Victoria (25) ([dagger])       1990-1999   4,502,000     804

Denmark
  Northern Jutland (21)          1996-1998    493 000      155
  Whole of Denmark (17)            2002      5,350,000    1,488
    ([double dagger])
Ireland (23) ([section])           1999      3,700,000     ND *

United Kingdom
  England(20,22) ([paragraph])   2002-2003   49,200,000   18,403
                                   2003                   19,244
  Northern Ireland (22,24) (#)     2002      1,697,000     397
                                   2003                    569
  Wales (22) (#)                   2003      2,920,000     742
USA
  Connecticut (14) **              1998      1,124,337     634

Country                          SAB/[10.sup.5]/y   % MRSA

Australia
  Present report                        35            27
  Victoria (25) ([dagger])              27            28

Denmark
  Northern Jutland (21)                 31            ND
  Whole of Denmark (17)                 28           0.6
    ([double dagger])
Ireland (23) ([section])                25            36

United Kingdom
  England(20,22) ([paragraph])          37            40
                                        39            41
  Northern Ireland (22,24) (#)          23            38
                                        34            44
  Wales (22) (#)                        25            47
USA
  Connecticut (14) **                   56           ND *

* MRSA, methicillin-resistant Staphylococcus aureus; ND, no data given.

([dagger]) In Victoria, 8,036 SAB episodes were reported, resulting in
a rate of 17.8/100,000. The final rate (27.0) for the entire state was
figure. The Victorian scheme is estimated to capture about two thirds
of all bacteremia episodes that occur in that state per year.

([double dagger]) System in place in Denmark since 1960, with numbers
of episodes continually rising (e.g., in 1966, 400 per year and total
population 4.8 million or 8/100,000). Collection data based on
reviewing all discharge summaries and laboratory samples (15 of 16
counties). Associated 23% mortality rate in 2002, and 22% of these
deaths were directly related to sepsis.

([section]) Rates in different regions varied from 8.9 to 37.1 per
100,000. Likely underreporting (22).

([paragraph]) Compulsory reporting system. Unclear if all community
onset episodes were included. In England, underreporting occurred when
a voluntary system was in place (only 13,770 episodes reported for
2003; thus, a 50% increase with compulsory system) (22).

(#) This rate is based on voluntary reporting system. Real rate might
be 50% higher (22,24).

** Retrospective case analysis. Rate increased with age, urban areas,
and African American ethnicity. 15% of community-onset SAB episodes
were MRSA.

Acknowledgments

We greatly appreciate the assistance of the many laboratory staff members at each of the participating hospitals and as well as many infection control practitioners who assisted in the collection of the data.

The Australian Group for Antimicrobial Resistance is currently funded by a grant from the Department of Health and Aging of the Australian Government with funding in the past from Eli Lilly (no funds received for 3 years).

The Australian Group on Antimierobial Resistance (AGAR) is a group that represents 21 teaching hospital microbiology laboratories and 5 private laboratories. AGAR meets every 6 months. At these meetings, Drs. Gottlieb and Collignon made the initial proposal for this project. All members of AGAR were able to participate in the discussion of the project and suggest modifications of the project design. Only 10 hospital laboratories had collected details on all their S. aureus bacteremia data prospectively, and these formed the AGAR participants able to participate in this study. Archie Darbar and Denise Daley were involved in the collection of data at their hospitals. Jan Roberts was involved in the collection of data at her hospital and also in the spreadsheet analysis of the data of all the participating hospitals.

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Peter Collignon, * Graeme R. Nimmo, ([dagger]) Thomas Gottlieb, ([double dagger]) and Iain B. Gosbell ([section]), on behalf of the Australian Group on Antimicrobial Resistance (1)

* The Canberra Hospital, Garran, Australian Capital Territory, Australia; ([dagger]) Queensland Health Pathology Service, Brisbane, Queensland, Australia; ([double dagger]) Concord Hospital, Concord, New South Wales, Australia; and ([section]) Southwestern Area Pathology Service, Liverpool, New South Wales, Australia

(1) Australian Group on Antimicrobial Resistance contributors to this study were the following: Thomas Gottlieb, Concord Hospital; David McGechie, Denise Daley, Fremantle Hospital; John Ferguson, John Hunter Hospital; James Branley, Nepean Hospital; Graeme R. Nimmo, Princes Alexandria Hospital; Gary Lum, Royal Darwin Hospital; Alistair McGregor, Royal Hobart Hospital; Clarence Fernandes, Royal North Shore Hospital; Iain Gosbell, Archie Darbar, South West Area Health Service, New South Wales; Peter Collignon, Jan Roberts, Canberra Hospital.

Drs. Collignon, Nimmo, Gottlieb, and Gosbell were involved in the writing of the manuscript. They made substantial contributions to the conception and design of the study, as well as to the acquisition, analysis, and interpretation of data. They also drafted the article and revised it critically for intellectual content. Additionally, all of the other participants in this AGAR project provided comment and feedback on numerous drafts over a 6month period. All authors have reviewed this version and given final approval for publication.

Dr. Collignon is an infectious diseases physician as well as a pathologist in clinical microbiology. He is a professor at the Canberra Clinical School of the Australian National University. His major research interests include antimicrobial resistance from medical use and in food animals and hospital-acquired infections, particularly bloodstream infections resulting from use of intravascular catheters.

Address for correspondence: Peter Collignon, Infectious Diseases Unit and Microbiology Department, The Canberra Hospital, PO Box 11, Woden, Australian Capital Territory 2602, Australia; fax: [phone]; email: [e-mail]