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ABCs Report: Methicillin-Resistant Staphylococcus aureus, 2011

Active Bacterial Core Surveillance (ABCs): Emerging Infections Program Network

Print-friendly version of this surveillance report [3 pages]

ABCs Areas

California (3 county San Francisco Bay area); Colorado (5 county Denver area); Connecticut; Georgia (8 county Atlanta area); Maryland (Baltimore City and County); Minnesota (2 metro Twin City counties); New York (1 Rochester county); Oregon (3 county Portland area); Tennessee (1 Nashville county).

ABCs Population

The surveillance areas represent 19,393,677 persons
Source: National Center for Health Statistics bridged race vintage 2011 postcensal file.

ABCs Case Definition

Invasive methicillin-resistant Staphylococcus aureus (MRSA) disease: isolation of MRSA from a normally sterile site in a resident of the surveillance area in 2011. Cases of disease are classified into one of three epidemiologic classifications. A case is classified as hospital-onset (HO) if the MRSA culture was obtained on or after the fourth calendar day of hospitalization, where admission is hospital day 1; as healthcare-associated community-onset (HACO) if the culture was obtained in an outpatient setting or before the fourth calendar day of hospitalization and had one of more of the following: 1) a history of hospitalization, surgery, dialysis, or residence in a long term care facility in the previous year, or 2) the presence of a central vascular catheter (CVC) within 2 days prior to MRSA culture; and as community-associated (CA) if none of the previously mentioned criteria are met.

ABCs Methodology

ABCs personnel routinely contacted all microbiology laboratories serving acute care hospitals in their area to identify cases. Standardized case report forms that include information on demographic characteristics, clinical syndrome, and outcome of illness were completed for each identified case. Convenience samples of isolates were collected and sent to CDC for routine testing, including: antimicrobial susceptibility testing, toxin testing and SCCmec typing. Pulsed field gel electrophoresis (PFGE) of all isolates was discontinued in 2008; an inferred PFGE algorithm was developed based on microbiologic and molecular characteristics of isolates. The algorithm has been validated for use with isolates collected though this surveillance only (http://www.cdc.gov/HAI/settings/lab/inferred-PFGE-algorithm.html). Regular laboratory audits were performed to ensure completeness of case detection.

Rates of invasive MRSA disease among all patients were calculated using population estimates for 2011. Cases with unknown race were assigned race based on distribution of known race and gender by EIP site. Confidence intervals for nationally estimated incidence rates of disease and mortality were calculated based on the gamma distribution (Stat Med, 1997 16:791-801).

Rates of invasive MRSA disease among patients who were undergoing chronic dialysis treatment were calculated using the December 31, 2010 point prevalent counts of patients on dialysis from the United States Renal Data System (USRDS) (http://www.usrds.org/adr.htm).

ABCs Results

Reported Race among 4872 Cases
Race No. (Ratea)
White 2743 (20.1)
Black 1542 (41.5)
Other 126 (6.2)

Unknown race (n=461) distributed amongst known

aCases per 100,000 population for ABCs areas (crude rates).

Reported Cases on Chronic Dialysis (n=960)
Dialysis and Access Type No. (%)
Peritoneal 30 (3.1)
Hemodialysis 929 (96.9)
AV Fistula/Graft 348 (37.5)
CVC 511 (55.0)
Unkown 70 (7.5)
Unkown 1
Distribution of cases, deaths and PFGE type by Epidemiological Classification
MRSA Class No. (Rate)
Casesb
No. (Rate)
Deaths c
PFGE Type (N,%)d
Tot N
PFGE Type (N,%)d
USA100
PFGE Type (N,%)d
USA300
PFGE Type (N,%)d
USA500
Iberian
CA 1010 (5.2) 100 (0.5) 306 81 (26.5) 192 (62.8) 9 (2.9)
HCAa 3780 (19.5) 532 (2.7) 986 478 (48.5) 312 (31.6) 88 (8.9)
HCA-HO 868 (4.5) 182 (0.9) 220 122 (55.5) 56 (25.5) 17 (7.7)
HCA-HACO 2912 (15.0) 350 (1.8) 766 356 (46.5) 256 (33.4) 71 (9.3)

aHCA: Healthcare-associated invasive MRSA infections; sum of patients that are classified as either HO or HACO.
bn=82; epidemiologic category unknown.
cn=18; epidemiologic category unknown.
disolates were eligible for testing at CDC

Reported Clinical Syndrome by Epidemiologic Class
Syndromea CA
(n=1010)
No. (%)
HACO
(n=2912)
No. (%)
HO
(n=868)
No. (%)
Bloodstream Infection with other syndromeb 528 (52.3) 1503 (51.6) 313 (36.1)
Bloodstream Infection with no other syndromeb 246 (24.4) 949 (32.6) 306 (35.3)
Pneumonia 161 (15.9) 441 (15.1) 146 (16.8)
Lower Respiratory Infectionc 52 (5.2) 127 (4.4) 58 (6.7)
Osteomyelitis 130 (12.9) 316 (10.9) 113 (13.0)
Endocarditis 74 (7.3) 150 (5.2) 48 (5.5)
Cellulitis 189 (18.7) 222 (7.6) 71 (8.2)
Wounds - Surgicald 15 (1.5) 185 (6.4) 34 (3.9)
Wounds - Decubitus/Pressure Ulcers 16 (1.6) 84 (2.9) 21 (2.4)
Other wounds/abscessese 7 0.5) 23 (0.8) 6 (0.7)
Traumatic Wounds 13 (1.3) 16 (0.6) 8 (0.9)

aSome case patients had more than one syndrome.
bSepsis or catheter site infection or AV fistula infection only are included in BSI with other syndrome.
cLower Respiratory Infection is defined as: a patient with pneumonia documented in their discharge summary, who has a positive MRSA non-sterile respiratory specimen with accompanying chest radiology results documenting any of the following: bronchopneumonia/pneumonia, air space density/opacity, new or changed infiltrates.
dCombines deep tissue/organ infection and infection of a surgical wound, post operatively.
eCategory includes skin abscess, necrotizing fasciitis, gangrene, non-traumatic wounds.

This figure is a bar chart that depicts the incidence, per one hundred thousand persons, of invasive MSRA (methicillin-resistant Staphylococcus aureus) by epidemiological class and age group in 2011. The three epidemiological classes charted are; community- associated (CA), healthcare-associated community-onset (HACO), and hospital-onset (HO). The eight age groups charted are; less than 1 year, 1 year, 2-4 years, 5-17 years, 18-34 years, 35-49 years, 50-64 years, greater than or equal to 65 years.
Table data for this chart

National Estimates and Adjusted Incidence Rates of Invasive MRSA Infections
Epidemiologic Category Estimated Cases of Infection
Non-Dialysis Patients Dialysis Patients Total
Estimated No. Incidence Rate (Confidence Interval)a Estimated No. Incidence Rate (Confidence Interval)b Estimated No. Incidence Rate (Confidence Interval)d
CA 16,560 5.32 (4.11-7.00) NA NA 16,560 5.31 (4.11-7.00)
HCA 47,340 15.21 (13.27-17.62) 15,169 3654.19 (2820.46-4739.00) 62,509 20.06 (17.01-23.91)
HCA-HO 12,464 4.01 (3.02-5.44) 1,692 407.71 (174.70-850.84) 14,156 4.54 (3.24-6.56)
HCA-HACO 34,876 11.21 (9.62-13.18) 13,477 3247.45 (2472.51-4246.00) 48,353 15.52 (12.90-18.82)
Overallc 65,296 20.98 (18.58-23.86) 15,169 3654.19 (2820.46-4739.00) 80,461 25.82 (22.31-30.14)

aNational Estimates and Incidence (no. per 100,000 population per year) are adjusted for age, race, gender and receipt of chronic dialysis using 2011 US Census Data.
bNational Estimates and Incidence (no. per 100,000 dialysis patients per year) for dialysis patients are adjusted for age, race and gender using 2010 USRDS point prevalence data.
c82 cases could not be classified into an epidemiological category or category is unknown and therefore are counted in the overall estimate only.
dStarting in 2011, confidence intervals on national estimates were determined for each of the 72 age/race/gender/dialysis specific strata and summarized for an overall national estimate, accounting for variance across all strata producing a more conservative estimate (with wider confidence intervals) compared to estimates prior to 2011.

National Estimates and Adjusted Incidence Rates for Mortality among Cases
Epidemiologic Class Estimated No. Mortality Rate
(Confidence Interval)a
CA 1,764 0.57 (0.30-1.04)
HCA 9,197 2.95 (2.02-4.54)
HCA-HO 3,126 1.00 (0.51-2.06)
HCA-HACO 6,071 1.95 (1.26-3.12)
Overallb 11,285 3.62 (2.58-5.31)

aNational Estimates and Mortality Rate (no. per 100,000 population per year) are adjusted for age, race, gender and receipt of chronic dialysis using 2011 US Census Data
b82 cases could not be classified into an epidemiological category or category is unknown and therefore are counted in the overall estimate only.

National Metric for Healthy People 2020 and the Department of Health and Human Services Action Plan to Prevent Healthcare-Associated Infections
  Disease Rate Estimate of Cases in United States.a
Baseline (07-08) 2011 % Change Baseline (07-08) 2011 Difference
HCA 27.08 20.06 -25.92 82,000 62,500 19,500

aDisease Rate (no. per 100,000 population per year) and National Estimates are adjusted for age, race, gender and receipt of chronic dialysis using 2011 US Census Data

ABCs Discussion

Surveillance data from 2011 represent the seventh full year of performing population-based surveillance for invasive MRSA infections through the Emerging Infections Program/Active Bacterial Core Surveillance Activity.

Overall, compared to the baseline incidence (2007-2008 calendar years) identified in the HHS Action Plan, there was a decrease of 25.92%.

Citation

  1. Centers for Disease Control and Prevention. 2011. Active Bacterial Core Surveillance Report, Emerging Infections Program Network, Methicillin-Resistant Staphylococcus aureus, 2011.
  2. Centers for Disease Control and Prevention. 2007. Invasive Methicillin-Resistant Staphylococcus aureus Infections Among Dialysis Patients — United States, 2005. MMWR. 2007; 56(09):197.

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