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ABCs Report: Methicillin-Resistant Staphylococcus aureus, 2007 (Update)

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

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ABCs Areas

California (3 county San Francisco Bay area); Colorado (5 Denver area county); Connecticut; Georgia (8 county Atlanta area); Maryland (1 Baltimore area county); Minnesota (1 metro Twin City county); New York (1 Rochester county); Oregon (3 county Portland area); Tennessee (1 Nashville county).
Note: the population under surveillance changed from 2006.

ABCs Population

The surveillance areas represent 16,968,233 persons.
Source: National Center for Health Statistics bridged-race vintage 2007 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 2007. 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; 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. 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 2007. Cases with unknown race were assigned race based on distribution of known race and gender by EIP site. Methodology to make national estimates was modified in January 2012 to adjust for receipt of dialysis, as well as age, race, and gender. Previously reported national estimates were adjusted for age and race only. Confidence intervals for nationally estimated incidence rates of disease and mortality were calculated based on the gamma distribution (Stat Med, 1997 16:791-801).

ABCs Results

ABC Racial/Ethnic Profiles
Race No. (Rate)a
White 3,408 (27.8)
Black 2,109 (66.6)
Other 179 (11.5)

Unknown race (n=739) distributed amongst known

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

PFGE Type by Antibiotic Resistance
PFGE Type (%) % PVL Pos. Clinda-Ra T/S-Rb Levo-Rc
USA100 (21.2) 0 98.7 0.2 99.5
USA300 (28.7) 95.1 8.3 2.1 52.2
USA500 (4.0) 1.5 38.2 82.4 88.2
USA800 (1.9) 0 47.4 0 63.2
IBERIAN (1.8) 3.7 40.0 70.0 100
OTHER (12.4) 12.7 44.2 7.0 53.5

a% Clindamycin resistant
b% Trimethoprim-sulfamethoxazole resistant
c% Levofloxicin resistant

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 908 (5.4) 72 (0.4) 200 52 (26) 131 (65.5) 8 (4.0)
HCAa 4,700 (27.7) 811 (4.8) 1,113 623 (56.0) 242 (21.7) 68 (6.1)
HCA-HO 1,402 (8.3) 341 (2.0) 350 61 (17.3) 207 (29.1) 46 (6.0)
HCA-HACO 3,298 (19.4) 470 (2.8) 763 95 (12.5) 189 (27.8) 17 (2.2)

aHCA: Healthcare-associated invasive MRSA infections; sum of patients that are classified as either HO or HACO.
bn=88; epidemiologic category unknown.
cn=9; epidemiologic category unknown.
disolates were eligible for testing at CDC

Reported Clinical Syndrome by Epidemiologic Class
Syndromea CA
(n=908)
HACO
(n=3,298)
HO
(n=1,402)
Bloodstream Infection with other syndrome 499 1,590 479
Bloodstream Infection with no other syndrome 232 1,319 688
Pneumonia 128 379 221
Osteomyelitis 112 307 100
Endocarditis 84 200 42
Cellulitis 162 269 66
Wounds - Surgicalb 9 160 50
Wounds - Decubitus/Pressure Ulcers 8 77 27
Other wounds/abscessesc 44 67 26
Traumatic Wounds 9 15 10

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

National Estimates and Adjusted Incidence Rates of Invasive MRSA Infections
Epidemiologic Class Estimated No. Incidence Rate
(Confidence Interval)a
CA 15,772 5.23 (4.89-5.6)
HCA 83,340 28.27 (27.45-29.12)
HO 25,356 8.41 (7.96-8.88)
HACO 57,984 19.22 (18.55-19.92)
Overallb 102,672 34.04 (33.14-34.97)

aNational Estimates and Incidence (no. per 100,000 population per year) are adjusted for age, race, gender, and receipt of dialysis treatment using 2007 US Census Data.
b88 cases could not be classified into an epidemiological category or category is unknown and therefore are counted in the overall estimate only.

Incidence of Invasive MRSA by Epidemiological Class and Age Group 2007
Table data for this chart

National Estimates and Adjusted Incidence Rates for Mortality among Cases
Epidemiologic Class Estimated No. Mortality Rate
(Confidence Interval)a
CA 1,147 0.38 (0.29-0.49)
HCA 15,206 5.12 (4.76-5.50)
HO 6,323 2.10 (1.87-2.34)
HACO 8,883 2.95 (2.68-3.24)
Overallb 16,881 5.60 (5.23-5.99)

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 2007 US Census Data.
b9 cases could not be classified into an epidemiological category or category is unknown and therefore are counted in the overall estimate only.

ABCs Discussion

Surveillance data from 2007 represent the third full year of performing population-based surveillance for invasive MRSA infections through the Emerging Infections Program/Active Bacterial Core Surveillance Activity. national estimates and calculate incidence rates was modified in January 2012 to adjust for receipt of dialysis, as well as age, race, and gender. Previously reported national estimates were adjusted for age and race only.

Citation

Centers for Disease Control and Prevention. 2007. Active Bacterial Core Surveillance Report, Emerging Infections Program Network, Methicillin-Resistant Staphylococcus aureus, 2007.


Footnote

Last Updated: January 30, 2012; See methods and discussion for update explanation.

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