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

September 27, 2017: 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 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)	179	45 (25)	121 (68)	6 (3)
HCAa	4,700 (27.7)	811 (4.8)	891	552 (62)	214 (24)	59 (7)
HCA-HO	1,402 (8.3)	341 (2.0)	274	181 (66)	48 (18)	19 (7)
HCA-HACO	3,298 (19.4)	470 (2.8)	617	371 (60)	166 (27)	40 (6)

^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.

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.

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