Monday, May 29, 2023
| Characteristic† |
Total no. (%),
N = 1,323 |
USA type | p value | |
|
No. (%) USA300/400,
n = 26 |
No. (%) other,‡
n = 1,297 |
|||
| Mean age, y | 67.8 (SD = 17.6) | 46.0 (SD = 22.0) | 68.2 (SD = 17.2) | <0.0001 |
| Female gender | 550 (41.6) | 9 (34.6) | 541 (42.7) | 0.549 |
| Inpatient stay | 1,124 (85.0) | 24 (92.3) | 1,100 (84.8) | 1.000 |
| ICU admission | 221 (16.7) | 4 (15.4) | 217 (16.7) | 0.764 |
| Nosocomial infection | 346 (26.2) | 5 (19.2) | 341 (26.3) | 0.306 |
| Specimen type | <0.0001 | |||
| Blood | 1,256 (94.9) | 25 (96.2) | 1,231 (94.9) |
 |
| CSF | 9 (0.7) | 0 | 9 (0.7) |
|
| Joint fluid | 33 (2.5) | 1 (3.9) | 32 (2.5) |
|
| Pleural fluid | 8 (0.6) | 0 | 8 (0.6) |
|
| Other | 6 (0.5) | 0 (0.0) | 6 (0.5) |
|
| Iowa region | 0.054 | |||
| 1 | 32 (2.4) | 1 (3.9) | 31 (2.4) |
|
| 2 | 370 (28.0) | 10 (38.5) | 360 (27.8) |
|
| 3 | 335 (25.3) | 2 (7.7) | 333 (25.7) |
|
| 4 | 272 (20.6) | 4 (15.4) | 268 (20.7) |
|
| 5 | 140 (10.6) | 5 (19.2) | 135 (10.4) |
|
| 6 | 63 (4.8) | 4 (15.4) | 59 (4.5) |
|
| PVL | ND | ND | ND | ND |
| SCCmec IV | ND | ND | ND | ND |
Descriptive Epidemiology of Invasive MRSA in Iowa, USA, 1999-2005*
*MRSA, methicillin-resistant Staphylococcus aureus; ICU, intensive care unit; CSF, cerebrospinal fluid; PVL, Panton-Valentine leukocidin; SCCmec IV, staphylococcal chromosomal cassette mec type IV; ND, not done for all isolates.
†The number of patients missing data on specific variables: age = 13; gender = 11; inpatient = 85; ICU = 356; nosocomial = 358; specimen type = 11; Iowa Department of Public Health Reporting Region = 11.
‡Of the subset of isolates that were typed (N = 180), 173 (96%) were USA100. The remainder clustered with USA200 (3), USA500 (2), or did not match an existing USA type.
| Characteristic† |
Total no. (%),
N = 343 |
USA type | p value | |
|
No. (%) USA300/400,
n = 54 |
No. (%) other,‡
n = 289 |
|||
| Mean age, y | 66.3 (SD = 17.0) | 50.6 (SD = 21.2) | 69.2 (SD = 14.4) | <0.0001 |
| Female gender | 135 (39.4) | 14 (25.9) | 121 (41.9) | 0.059 |
| Inpatient stay | 278 (81.0) | 50 (92.6) | 228 (78.9) | 0.271 |
| ICU admission | 56 (16.3) | 8 (14.8) | 48 (16.7) | 0.348 |
| Nosocomial infection | 57 (16.6) | 1 (1.9) | 56 (19.4) | 0.0006 |
| Specimen type | 0.0021 | |||
| Blood | 322 (93.9) | 45 (83.3) | 276 (95.0) |
|
| CSF | 0 | 0 | 0 |
|
| Joint fluid | 13 (3.8) | 5 (9.3) | 8 (2.9) |
|
| Pleural fluid | 2 (0.6) | 2 (3.7) | 0 |
|
| Other | 6 (1.7) | 2 (3.7) | 5 (1.4) |
|
| Iowa region | 0.268 | |||
| 1 | 10 (2.9) | 0 | 10 (3.5) |
|
| 2 | 93 (27.0) | 13 (24.1) | 80 (27.7) |
|
| 3 | 49 (14.2) | 12 (22.2) | 37 (12.8) |
|
| 4 | 105 (30. 5) | 16 (29.6) | 88 (30.5) |
|
| 6 | 20 (5.8) | 5 (9.3) | 15 (5.2) |
|
| PVL | 54 (15.7) | 52 (96.3) | 2 (0.7)§ | <0.0001 |
| SCCmec IV | 68 (19.8) | 54 (100.0) | 13 (4.5) | <0.0001 |
Descriptive Epidemiology of Invasive MRSA in Iowa, USA, 2006*
*MRSA, methicillin-resistant Staphylococcus aureus; ICU, intensive care unit; CSF, cerebrospinal fluid; PVL, Panton-Valentine leukocidin; SCCmec IV, Staphylococcal chromosomal cassette mec type IV.
†The number of patients missing data on specific variables: age = 10; gender = 12; inpatient = 31; ICU = 122; nosocomial = 101; specimen type = 0; Iowa Department of Public Health Reporting Region = 6; PVL = 3; SCCmec IV = 3.
‡Of the subset of isolates that were typed (N = 272) 94% were USA100. The remainder clustered with USA200 (5), USA500 (5), USA600 (1), USA800 (4), or did not match an existing USA type.
§Both isolates clustered with USA100 and were SCCmecII.
| Antimicrobial agent | % Susceptible |
| Erythromycin | 9 |
| Levofloxacin | 57 |
| Clindamycin† | 93 |
| Tetracycline | 93 |
| Mupirocin | 98 |
| Rifampin | 98 |
| Trimethoprim/sulfamethoxazole | 100 |
| Vancomycin | 100 |
| Gentamicin | 100 |
| Daptomycin | 100 |
| Linezolid | 100 |
Antimicrobial Drug Susceptibility of 54 Invasive MRSA USA300/400 K, Iowa, USA, 2006*
*MRSA, methicillin-resistant Staphylococcus aureus.
†Includes D-testing of all erythromycin-resistant, clindamycin-susceptible isolates.
This activity is intended for primary care clinicians, infectious disease specialists, geriatricians, pediatricians, and other specialists who care for patients at risk for methicillin-resistant Staphylococcus aureus (MRSA) infection.
The goal of this activity is to differentiate risk factors for healthcare-associated and community-associated methicillin-resistant Staphylococcus aureus (MRSA) and the associated MRSA strains (USA300/400), and to report emerging patterns of community-associated MRSA in 1 US state from the period of 1999-2006.
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CME Released: 9/23/2009
Valid for credit through: 9/23/2010
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Abstract
We performed antimicrobial drug susceptibility testing and molecular typing on invasive methicillin-resistant Staphylococcus aureus (MRSA) isolates (n = 1,666) submitted to the University of Iowa Hygienic Laboratory during 1999-2006 as part of a statewide surveillance system. All USA300 and USA400 isolates were resistant to ≤3 non-β-lactam antimicrobial drug classes. The proportion of MRSA isolates from invasive infections that were either USA300 or USA400 increased significantly from 1999-2005 through 2006 (p<0.0001). During 2006, the incidence of invasive community-associated (CA)-MRSA infections was highest in the summer (p = 0.0004). Age <69 years was associated with an increased risk for invasive CA-MRSA infection (odds ratio [OR] 5.1, 95% confidence interval [CI] 2.06-12.64), and hospital exposure was associated with decreased risk (OR 0.07, 95% CI 0.01-0.51).
Introduction
Methicillin-resistant Staphylococcus aureus (MRSA) emerged in the 1960s and has since become a major cause of illness and death in the healthcare setting.[1,2] Risk factors for infection with healthcare-associated MRSA (HA-MRSA) include hospitalization, residence in a long-term care facility, older age, invasive devices (e.g., catheters, feeding tubes), and exposure to antimicrobial agents. HA-MRSA isolates are often resistant to several antimicrobial drug classes in addition to β-lactams.[3]
In the 1990s, investigators began describing serious MRSA infections among persons who did not have typical risk factors for infections with this organism.[2,4-8] These community-associated MRSA (CA-MRSA) infections affected young, healthy persons[4,5,7] and were associated with factors such as participating in contact sports, sharing towels or athletic equipment, using illegal intravenous drugs, and living in crowded or unsanitary areas (e.g., prisons, hurricane evacuee centers).[9,10]
Pulsed-field gel electrophoresis (PFGE) demonstrated that MRSA strains causing these community-associated infections (USA300 and USA400) were different than those causing healthcare-associated infections (USA100 and USA200).[11] USA300 and USA400 MRSA strains typically have the staphylococcal cassette chromosome (SCC) mec type IV, not the SCCmec type II carried by most USA100 and USA200 isolates.[12] In addition, USA300/400 isolates usually carry the gene that encodes the Panton-Valentine leukocidin (pvl), a bicomponent (lukF-PV and lukS-PV) pore-forming leukotoxin.[8,13-15] Currently, the role of PVL in the pathogenesis of infections caused by USA300/400 isolates is controversial. Epidemiologic studies and a study by Labandeira-Rey et al. suggest that PVL is associated with virulence and causes the necrosis characteristic of infections with these strains.[16] In contrast, a study by Voyich et al. found no difference in virulence between the wild-type parent strains and the isogenic knockout strains that did not produce PVL.[17]
A recent multicenter study by Moran et al. showed that USA300 MRSA is now the most common cause of skin and soft tissue infections (SSTIs) among adults seeking treatment in emergency departments in 11 large metropolitan areas.[15] USA300 also causes serious invasive infections such as necrotizing pneumonia, bloodstream infections, and surgical site infections, some of which are acquired in hospitals.[18-22] Although most USA300 and USA400 isolates are currently resistant to fewer classes of antimicrobial drugs than are HA-MRSA isolates,[13] a recent paper by Han et al. identified a USA300 subtype that is resistant to erythromycin, clindamycin (constitutive), tetracycline, mupirocin, and fluoroquinolones.[23]
Most epidemiologic studies of CA-MRSA have examined isolates from SSTIs infections,[7,15,18] and most studies that evaluated patients with invasive disease have involved single healthcare facilities[21,24] or isolates obtained primarily from large urban areas.[22] We describe the molecular epidemiology of invasive infections caused by USA300 and USA400 in a rural state. We characterized invasive MRSA from 1999-2005 (select isolates) and in 2006 (all isolates) submitted to the statewide surveillance system in Iowa for invasive MRSA infections.
