ABCs Report: Methicillin-Resistant Staphylococcus aureus, 2012

March 7, 2014: Content on this page kept for historical reasons.

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

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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 19,635,461 persons
Source: National Center for Health Statistics bridged race vintage 2012 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 2012. 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 healthcare facilities 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, SCCmec typing, and spa typing. Pulsed field gel electrophoresis (PFGE) of all isolates was discontinued in 2008; up until 2012, PFGE was inferred based on a validated algorithm. Starting in 2012, spa typing was added to the routine laboratory testing. Pulsed field type is currently inferred based on spa type, inferred MLST clonal complex and molecular characteristics of the isolates. In 2012, isolates were only collected in five sites (California, Georgia, Minnesota, New York, and Tennessee). 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 2012. 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, 2011 point prevalent counts of patients on dialysis from the United States Renal Data System (USRDS)External.

ABCs Results

Reported Race among 4582 Cases
Race No. (Ratea)
White 2869 (20.9)
Black 1554 (40.9)
Other 159 (7.6)

Unknown race (n=391) distributed amongst known

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

Reported Cases on Chronic Dialysis (n=869)
Dialysis and Access Type No. (%)
Peritoneal 29 (3.3)
Hemodialysis 832 (95.7)
Hemodialysis – AV Fistula/Graft 361 (43.4)
Hemodialysis – CVC 440 (52.9)
Hemodialysis – Unkown 31 (3.7)
Unkown 8
Cases, Deaths & Inferred PFGE type by Epidemiological Classification
MRSA Class No. (Rate)
Casesb
No. (Rate)
Deaths c
Inferred PFGE Type (%)
Tot N
Inferred PFGE Type (%)
USA100
Inferred PFGE Type (%
USA300
Inferred PFGE Type (%)
USA500/
Iberian
CA 937 (4.8) 85 (0.4) 145 30 (20.7) 100 (69.0) 5 (3.5)
HCAa 3565 (18.1) 475 (2.4) 535 267 (49.9) 150 (28.0) 69 (12.9)
HCA-HO 788 (4.0) 120 (0.6) 110 52 (47.3) 38 (34.6) 11 (2.7)
HCA-HACO 2777 (14.1) 355 (1.8) 425 215 (50.6) 112 (26.4) 58 (13.7)

aHCA: Healthcare-associated invasive MRSA infection; sum of patients that are classified as either the HO or HACO classes.
bn=80; epidemiologic category unknown.
cn=6; epidemiologic category unknown.

Reported Clinical Syndrome by Epidemiologic Class
Syndromea CA
(n=937)
No. (%)
HACO
(n=2777)
No. (%)
HO
(n=788)
No. (%)
Bloodstream Infection with other syndromeb 477 (50.9) 1368 (49.3) 251 (31.9)
Bloodstream Infection with no other syndromeb 170 (18.1) 850 (30.6) 262 (33.2)
Pneumonia 124 (13.2) 318 (11.5) 123 (15.6)
Pneumonia – Lower Respiratory Infectionc 34 (3.6) 87 (3.1) 45 (5.7)
Osteomyelitis 150 (16.0) 421 (15.2) 145 (18.4)
Endocarditis 67 (7.2) 135 (4.9) 25 (3.2)
Cellulitis 200 (21.3) 216 (7.8) 68 (8.6)
Wounds – Surgicald 19 (2.0) 191 (6.9) 51 (6.5)
Wounds – Decubitus/Pressure Ulcers 16 (1.7) 69 (2.5) 24 (3.1)
Wounds – Skin Abscessese 109 (11.6) 94 (3.4) 26 (3.3)
Wounds – Other woundsf 25 (2.7) 99 (3.6) 19 (2.4)
Wounds – Traumatic 13 (1.4) 12 (0.4) 8 (1.0)

aSome case patients had more than one syndrome.
bCatheter 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. Number of cases considered as skin abscess was expanded for the 2012 annual summary.
fCategory includes non-traumatic and other chronic wound infections.

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 2012. 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.
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 15,138 4.82 (3.69-6.42) NA NA 15,138 4.82 (3.69-6.42)
HCA 44,771 14.29 (12.40-16.62) 14,041 3262.39 (2496.82-4247.12) 58,812 18.74 (15.81-22.42)
HCA-HO 11,493 3.67 (2.73-5.02) 1,408 327.24 (131.31-739.07) 12,901 4.11 (2.90-6.02)
HCA-HACO 33,278 10.62 (9.06-12.55) 12,633 2936.08 (2216.06-3876.65) 45,911 14.63 (12.09-17.85)
Overallc 61,268 19.54 (17.24-22.31) 14,041 3263.31 (2496.12-4248.98) 75,309 23.99 (20.64-28.10)

aNational Estimates and Incidence (no. per 100,000 population per year) are adjusted for age, race, gender and receipt of chronic dialysis using 2012 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 2011 USRDS point prevalence data.
c80 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 1,444 0.46 (0.22-0.93)
HCA 8,128 2.59 (1.74-3.88)
HCA-HO 2,045 0.65 (0.31-1.35)
HCA-HACO 6,083 1.94 (1.23-3.10)
Overallb 9,670 3.08 (2.15-4.48)

aNational Estimates and Mortality Rate (no. per 100,000 population per year) are adjusted for age, race, gender and receipt of chronic dialysis using 2012 US Census Data
b80 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) 2012 % Change Baseline (07-08) 2012 Difference
HCA 27.08 18.74 -30.80 82,000 59,000 23,000

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 2012 represent the eighth 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 30.80%.

Citation

  1. Centers for Disease Control and Prevention. 2012. Active Bacterial Core Surveillance Report, Emerging Infections Program Network, Methicillin-Resistant Staphylococcus aureus, 2012.

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