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ABCs Report: Methicillin-Resistant Staphylococcus aureus, 2009

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 Denver area county); 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).
Note: the population under surveillance changed from 2008.

ABCs Population

The surveillance areas represent 19,311,576 persons.
Source: National Center for Health Statistics bridged-race vintage 2009 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 2009. 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 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 (). 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 2009. 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 are undergoing chronic dialysis treatment were calculated using the December 31, 2008 point prevalent counts of patients on dialysis from the United States Renal Data System (USRDS).

ABCs Results

ABC Racial/Ethnic Profiles
Race No. (Ratea)
White 3,301 (23.7)
Black 2,067 (57.6)
Other 237 (13.3)

Unknown race (n=642) distributed amongst known

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

Distribution of cases, deaths and PFGE type by Epidemiological Classification
MRSA Class No. (Rate)
Casesb
No. (Rate)
Deaths c
Inferred PFGE Type (N,%)d
Tot N
Inferred PFGE Type (N,%)d
USA100
Inferred PFGE Type (N,%)d
USA300
Inferred PFGE Type (N,%)d
USA500
Iberian
CA 982 (5.1) 102 (0.5) 300 63 (21.0) 213 (71.0) 9 (3.0)
HCAa 4,508 (23.3) 720 (3.7) 1,037 560 (54.0) 353 (34.0) 82 (8.9)
HCA-HO 1,198 (6.2) 281 (1.5) 264 150 (56.8) 80 (30.3) 28 (10.6)
HCA-HACO 3,310 (17.1) 439 (2.3) 773 410 (53.0) 273 (35.3) 64 (8.3)

aHCA: Healthcare-associated invasive MRSA infections; sum of patients that are classified as either HO or HACO.
bn=115; epidemiologic category unknown.
cn=10; epidemiologic category unknown.
disolates were eligible for testing at CDC

Reported Cases on Chronic Dialysis (n=1,003)
Dialysis and Access Type No. (%)
Type of dialysis
Peritoneal 28 (2.8)
Hemodialysis 973 (97.0)
Hemodialysis - AV Fistula/Graft 339 (34.8)
Hemodialysis - CVC 550 (56.5)
Hemodialysis - Unkown 84 (8.6)
Unkown 0.00
Reported Clinical Syndrome by Epidemiologic Class
Syndromea CA
(n=982)
HACO
(n=3,310)
HO
(n=1,198)
Bloodstream Infection with other syndrome 551 1,813 468
Bloodstream Infection with no other syndrome 205 1,063 461
Pneumonia 175 461 243
Lower Respiratory Infectionb 61 123 93
Osteomyelitis 125 374 114
Endocarditis 79 178 44
Cellulitis 175 260 70
Wounds - Surgicalc 15 194 59
Wounds - Decubitus/Pressure Ulcers 32 150 35
Other wounds/abscessesd 16 39 9
Wounds - Traumatic 18 13 12

aSome case patients had more than one syndrome.
bLower 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.
cCombines deep tissue/organ infection and infection of a surgical wound, post operatively.
dCategory includes skin abscess, necrotizing fasciitis, gangrene, non-traumatic wounds.

Incidence of Invasive MRSA by Epidemiological Class and Age Group 2009

National Estimates and Adjusted Incidence Rates for Mortality among Cases
Epidemiologic Class Estimated No. Mortality Rate
(Confidence Interval)a
CA 1,675 0.55 (0.44-0.67)
HCA 12,262 4.00 (3.71-4.32)
HCA-HO 4,786 1.56 (1.38-1.77)
HCA-HACO 7,476 2.44 (2.21-2.69)
Overallb 14,100 4.59 (4.28-4.93)

aNational Estimates and Mortality Rate (no. per 100,000 population per year) are adjusted for age, race, gender and receipt of dialysis treatment in the using 2009 US Census Data.
b10 cases could not be classified into an epidemiological category or category is unknown and therefore are counted in the overall estimate only.

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)
CA 15,211 4.96 (4.65-5.29) NA NA 15,211 4.96 (4.65-5.29)
HCA 56,785 18.53 (17.91-19.17) 16,094 4,190.52 (3,926.26-4,474.32) 72,879 23.75 (23.04-24.47)
HCA-HO 17,294 5.64 (5.30-6.00) 1,941 505.94 (414.97-618.29) 19,235 6.27 (5.91-6.65)
HCA-HACO 39,491 12.88 (12.36-13.42) 14,153 3,688.96 (3,441.69-3,955.81) 53,644 17.47 (16.87-18.10)
Overallc 73,810 24.07 (23.37-24.79) 16,056 4,184.99 (3,921.04-4,468.50) 89,867 29.27 (28.49-30.08)

aNational Estimates and Incidence (no. per 100,000 population per year) are adjusted for age, race, gender, and receipt of dialysis treatment using 2009 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 2008 USRDS point prevalence data.
c115 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) 2009 % Change Baseline (07-08) 2009 Difference
HCA 27.08 23.75 -12.3 82,000 72,900 -9,100

aDisease Rate (no. per 100,000 population per year) and National Estimates are adjusted for age, race, gender and receipt of chronic dialysis using 2009 US Census Data

ABCs Discussion

Surveillance data from 2009 represent the fifth full year of performing population-based surveillance for invasive MRSA infections through the Emerging Infections Program/Active Bacterial Core Surveillance Activity. Several changes in operations include addition of new variables to capture details on dialysis and access type and presentation of target measures to evaluate the reduction of healthcare-associated invasive MRSA infections.

Tables/figures have been added to (1) summarize details regarding type of dialysis and the type of access used for hemodialysis, indicating the majority of cases on chronic dialysis treatment were using central venous catheter for hemodialysis at the time of invasive MRSA culture; and (2) report metrics to measure progress in prevention of healthcare-associated invasive MRSA infections in the United States as part of Healthy People 2020 and the Department of Health and Human Services Action Plan to Prevent Healthcare-Associated Infections. Overall, compared to the baseline incidence (2007-2008 calendar years) identified in the HHS Action Plan, there was a decrease of 12.3%: a decrease on course to reach the target of a 50% reduction in 2013.

Because incidence of invasive MRSA infection is higher among dialysis patients compared to the general population,2 and increasing awareness and importance is being placed on preventing bloodstream infections among this population in the United States, we are displaying national estimates overall, and separately for dialysis and non-dialysis patients. Also, adjustment for dialysis was refined to account for receipt of chronic dialysis only whereas previous reports adjusted for receipt of chronic and acute dialysis in the past year. Receipt of acute dialysis accounts for ˜7% of all cases with a history of dialysis in the prior year.

Citation

  1. Centers for Disease Control and Prevention. 2009. Active Bacterial Core Surveillance Report, Emerging Infections Program Network, Methicillin-Resistant Staphylococcus aureus, 2009.
  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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