Management by Primary Care Clinicians of Patients Suspected of Having Community-Acquired Methicillin-Resistant Staphylococcus Aureus Infections

Results (continued)

Univariate Analysis of SSTIs

The univariate findings for procedures and cultures were performed only on 680.x ICD-9 codes, because the majority of 681.x-682.x codes are cellulitis, for which procedures and cultures cannot be done. There was a significant decrease in the procedure rate in WHA and combined systems, but not in MCNT (Table 4). However, overall, the procedure rate was unexpectedly low, as was the culture rate. The culture rate was higher than the procedure rate, which suggests that in some cases cultures were obtained even though there was no procedure performed or the procedure was not detected in the electronic billing data.

Table 4. Pre-intervention and intervention rates for procedures and cultures of purulent SSTIs (680.x)

  MCNT WHA Combined
  Pre Intervention p Value Pre Intervention p Value Pre Intervention p Value
Total cases (n) 118 46   175 102   293 148  
Procedures (n) 2 2   28 5   30 7  
Procedures (%) 1.69 4.35 0.3225 16.09 4.9 0.0060 10.27 4.73 0.0488
Culture (n) 21 3   29 18   50 21  
Culture (%) 17.8 6.52 0.0665 16.67 17.65 0.8181 17.12 14.19 0.4378

Key: MCNT = Medical Clinic of North Texas, WHA = Wilmington Health Associates.

In total, there were 316 cultures that were positive for S. aureus in the two systems; of these, 208 (65.8 percent) were MRSA. MRSA was highly prevalent in both systems prior to the intervention, and this did not substantially change during the intervention period. Table 5 shows the breakdown by time period and system.

Table 5. Proportion of S. aureus cultures that were MRSA

  MCNT WHA Combined
Pre-intervention 91/139 (65.5%) 69/106 (65.1%) 160/245 (65.3%)
Intervention 12/21 (57.1%) 36/50 (72.0%) 48/71 (67.6%)
All time periods 103/161(64.0%) 105/156 (67.3%) 208/316 (65.8%)

Key: MCNT = Medical Clinic of North Texas, WHA = Wilmington Health Associates.

For antibiotic usage and antibiotic choice (whether MRSA was covered when antibiotics were prescribed), the univariate analysis was performed separately on 680.x infections (Table 6 and Figure 1) and 681.x-682.x infections (Table 7 and Figure 2). This was because the antibiotics may be less indicated in general for a purulent infection that is fully drained (which may include most of 680.x cases) but, when used, should cover MRSA. For 681.x-682.x cases, of which the majority may be cellulitis infections that are not purulent, antibiotics are clearly indicated and coverage of MRSA is less imperative, according to the CDC guidelines. The combined 680.x-682.x is also presented below (Table 8). Compared to the pre-intervention period, antibiotic use increased in both systems for all ICD-9 groupings during the intervention period. The proportion of antibiotics that covered MRSA increased significantly in WHA and the two systems combined in the 681.x-682.x and all ICD-9 codes combined, whereas there was a trend for an increase in MRSA antibiotic use in MCNT within the 681.x-682.x and all ICD-9 codes combined. In the 680.x cases, there was a trend for increased MRSA antibiotic usage in WHA. Clinicians in MCNT used antibiotics more often than in WHA.

Table 6. Antibiotic usage for purulent cases (680.x) and if MRSA-covering antibiotic

  MCNT WHA Combined
  Pre-Intervension Intervention p Value Pre-Intervention Intervention p Value Pre-Intervention Intervention p Value
Total number of 680.x cases (n) 118 46   175 102   293 148  
Antibiotics prescribed (n) 63 32   44 37   107 69  
Antibiotics prescribed (%) 53.39 69.57 0.0594 25.14 36.27 0.0495 36.52 46.62 <.0001
MRSA-covering antibiotics (n) 34 18   9 14   43 32  
MRSA-covering antibiotics (%) 53.97 56.25 0.8328 20.45 37.84 0.0839 40.19 46.38 0.4175

Key: MCNT = Medical Clinic of North Texas, WHA = Wilmington Health Associates.

Figure 1. 680.x Skin infections and antibiotic prescribing rates in WHA, MCNT, and combined

Figure 1. 680.x Skin infections and antibiotic prescribing rates in WHA, MCNT, and combined. Select below for Text Description.

Key: MCNT = Medical Clinic of North Texas, WHA = Wilmington Health Associates.

[D] Select for Text Description.

Table 7. Antibiotic usage for 681.x-682.x cases and if MRSA-covering antibiotic

  MCNT WHA Combined
  Pre-0 Intervention Intervention p Value Pre-Intervention Intervention p Value Pre-Intervention Intervention p Value
Total number of 681.x-682.x cases 1752 597   1067 661   2819 1258  
Antibiotics prescribed (n) 738 368   265 202   1003 570  
Antibiotics prescribed (%) 42.12 61.64 <.0001 24.84 30.56 0.0092 35.58 45.31 <.0001
MRSA-covering antibiotics (n) 289 166   49 56   338 222  
MRSA-covering antibiotics (%) 39.16 45.11 .0582 18.49 27.72 0.0179 33.7 38.95 0.0366

Figure 2. 681.x�682.x Skin infections and antibiotic prescribing rates in WHA, MCNT, and combined

Figure 2. 681.x�682.x Skin infections and antibiotic prescribing rates in WHA, MCNT, and combined. Go to Text Description linked below.

Key: MCNT = Medical Clinic of North Texas, WHA = Wilmington Health Associates.

[D] Select for Text Description.

Table 8. Antibiotic usage for all SSTI (680.x-682.x) cases and if MRSA-covering antibiotic

  MCNT WHA Combined
  Pre-Intervention Intervention p Value Pre-Intervention Intervention p Value Pre-Intervention Intervention p Value
Total number of cases 1870 643   1240 802   3110 1447  
Antibiotics prescribed (n) 801 400   309 239   1110 639  
Antibiotics prescribed (%) 42.83 62.21 <.0001 24.88 31.32 <.0017 35.67 45.45 <.0001
MRSA-covering antibiotics (n) 323 184   58 70   381 254  
MRSA-covering antibiotics (%) 40.32 46 .0605 18.77 29.29 0.0039 34.32 39.75 0.0231

Key: MCNT = Medical Clinic of North Texas, WHA = Wilmington Health Associates.

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Multivariate Analyses

The multivariate analyses adjusted for patient demographic and clinical characteristics and the findings are presented in the tables below (Tables 9-16). The intervention was associated with a trend toward a decreased likelihood of performing a drainage procedure but no significant effect on obtaining cultures (680.x cases only). The intervention increased the likelihood of prescribing antibiotics and that the antibiotics prescribed would cover MRSA.

Procedures

Table 9. Odds ratio estimates for procedures performed on purulent SSTIs (680.x)
n=436 total cases in this regression

Effect Odds Ratio 95% Confidence Limits p Value
Intervention period
n=148 cases that were in intervention period
0.3642 0.1124 1.1796 0.0921
Child or adolescent
n=144 children/adolescents
3.1741 1.0071 10.0035 0.0486
Male
n=191 males
2.2339 1.2897 3.8692 0.0041
Previous case of MRSA
n=86 with a previous case
0.7231 0.3465 1.509 0.3877
MCNT patient
n=164 from MCNT
0.3878 0.095 1.5836 0.187
Diabetes
n=60 with diabetes
2.3839 0.7737 7.3455 0.1303
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
0.7122 0.1703 2.9785 0.642
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
0.2323 0.0451 1.1957 0.0808
Specialty: Peds vs. FM
n=131 patients of Peds
0.615 0.1531 2.4702 0.4932

Key: MCNT = Medical Clinic of North Texas, IM = internal medicine, FM = family medicine, PA = physician assistant, NP = nurse practitioner, Peds = pediatrics.

Cultures

Table 10. Odds ratios for cultures obtained on purulent SSTIs (680.x)
n=436 total cases in this regression

Effect Odds Ratio 95% Confidence Limits p Value
Intervention period
n=148 cases that were in intervention period
0.9354 0.5255 1.665 0.8204
Child or adolescent
n=144 children/adolescents
1.9468 0.7196 5.2672 0.1896
Male
n=191 males
1.8485 1.1097 3.0793 0.0183
Previous case of MRSA
n=86 with a previous case
0.5692 0.3235 1.0015 0.0506
MCNT patient
n=164 from MCNT
0.5563 0.2373 1.304 0.1772
Diabetes
n=60 with diabetes
1.2438 0.5756 2.688 0.5789
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
2.206 0.5535 8.7918 0.2621
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
8.9855 2.1632 37.3245 0.0025
Specialty: Peds vs. FM
n=131 patients of Peds
2.4239 0.575 10.2187 0.2278

Antibiotics

Table 11. Among 680.x cases, odds ratios for receiving antibiotics
n=436 total cases in this regression

Effect Odds Ratio 95% Confidence Limits p Value
Intervention period
n=148 cases that were in intervention period
2.183 1.4429 3.3026 0.0002
Child or adolescent
n=144 children/adolescents
0.3628 0.1488 0.8846 0.0258
Male
n=191 males
1.0333 0.6821 1.5651 0.8773
Previous case of MRSA
n=86 with a previous case
0.8014 0.4327 1.484 0.4812
MCNT patient
n=164 from MCNT
2.7345 1.5667 4.7726 0.0004
Diabetes
n=60 with diabetes
0.5532 0.323 0.9477 0.0311
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
0.6585 0.3786 1.1451 0.1389
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
1.6038 0.696 3.6957 0.2674
Specialty: Peds vs. FM
n=131 patients of Peds
2.597 1.028 6.559 0.0436

Key: MCNT = Medical Clinic of North Texas, IM = internal medicine, FM = family medicine, PA = physician assistant, NP = nurse practitioner, Peds = pediatrics.

Table 12. Among all cases (680-2.x), odds ratios for receiving antibiotics
n = 4,457 total cases in this regression

Effect Odds Ratio 95% Confidence Limits p Value
Intervention
n=1,406 cases that were in intervention period
1.7806 1.4921 2.1248 <.0001
Child or adolescent (age<18)
n=1,105 children/adolescents
1.0557 0.8539 1.3051 0.6168
Male
n=815 males
1.1009 0.9851 1.2302 0.0899
Previous case of MRSA
n=708 with a previous case
0.9287 0.7609 1.1336 0.4672
MCNT patient
n=2,513 patients from MCNT
3.0809 2.4068 3.9438 <.0001
Diabetes
n=767 patients with diabetes
0.8595 0.7145 1.0339 0.1083
Specialty. IM vs. FM
n=1,483 patients of IM
n=1,637 patients of FM
0.8586 0.6109 1.2067 0.3801
Specialty: PA/NP vs. FM
n=522 patients of PA/NP
1.0849 0.6606 1.7818 0.7474
Specialty: Peds vs. FM
n=815 patients of Peds
1.2664 0.9208 1.7416 0.1464
ICD-9 of 680.x vs. 681.x-682.x
n=441 patients with a 680.x diagnosis
1.0279 0.8041 1.3140 0.8260

Key: MCNT = Medical Clinic of North Texas, IM = internal medicine, FM = family medicine, PA = physician assistant, NP = nurse practitioner, Peds = pediatrics, ICD-9 = International Classification of Diseases-9.

MRSA-covering antibiotics

Table 13. 680.x cases only, odds ratios for receiving a MRSA-covering antibiotic
n=436 total cases in this regression

Effect Odds Ratio 95% Confidence Limits p Value
Intervention period
n=148 cases that were in intervention period
2.6241 1.4955 4.6044 0.0008
Child or adolescent
n=144 children/adolescents
1.1417 0.5803 2.2462 0.701
Male
n=191 males
1.2734 0.7252 2.236 0.4002
Previous case of MRSA
n=86 with a previous case
1.165 0.4693 2.8921 0.742
MCNT patient
n=164 from MCNT
4.2918 2.2836 8.0662 <.0001
Diabetes
n=60 with diabetes
0.9262 0.4455 1.9255 0.8373
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
2.762 0.9884 7.7178 0.0527
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
6.509 2.416 17.54 0.0002
Specialty: Peds vs. FM
n=131 patients of Peds
2.459 0.733 8.245 0.1449

Key: MCNT = Medical Clinic of North Texas, IM = internal medicine, FM = family medicine, PA = physician assistant, NP = nurse practitioner, Peds = pediatrics.

Table 14. Among all cases 680.x-682.x, odds ratios for receiving a MRSA-covering antibiotic
n=4,457 total cases for this regression

Effect Odds Ratio 95% Confidence Limits pValue
Intervention
n=1,406 cases that were in intervention period
1.9352 1.5321 2.4444 <.0001
Child or adolescent(age<18)
n=1,105 children/adolescents
0.8270 0.5986 1.1426 0.2495
Male
n=815 males
1.1615 0.9960 1.3545 0.0563
Previous case of MRSA
n=708 with a previous case
0.9218 0.6981 1.2170 0.5656
MCNT patient
n=2,513 patients from MCNT
4.4009 3.0793 6.2899 <.0001
Diabetes
n=767 patients with diabetes
0.8847 0.6961 1.1243 0.3164
Specialty. IM vs. FM
n=1,483 patients of IM
n=1,637 patients of FM
0.7604 0.4939 1.1708 0.2136
Specialty: PA/NP vs. FM
n=522 patients of PA/NP
1.2127 0.7751 1.8974 0.3984
Specialty: Peds vs. FM
n=815 patients of Peds
1.7964 1.1568 2.7896 0.0091
ICD-9 of 680.x vs. 681.x-682.x
n=441 patients with a 680.x diagnosis
1.5935 0.9837 2.5811 0.0583

Key: MCNT = Medical Clinic of North Texas, IM = internal medicine, FM = family medicine, PA = physician assistant, NP = nurse practitioner, Peds = pediatrics, ICD-9 = International Classification of Diseases-9

Table 15. If an antibiotic was prescribed (680.x-682.x cases), odds ratios for receiving a MRSA-covering antibiotic (model excludes cases in which no antibiotic was prescribed)
n=1,717 total cases in this regression

Effect Odds Ratio 95% Confidence Limits p Value
Intervention
n=626 cases that were in intervention period
1.4108 1.0803 1.8425 0.0115
Child or adolescent (age<18)
n=452 children/adolescents
0.7169 0.4911 1.0466 0.0847
Male
n=815 males
1.1253 0.9144 1.3847 0.2649
Previous case of MRSA
n=271 with a previous case
1.0132 0.7444 1.3790 0.9336
MCNT patient
n=1,173 patients from MCNT
2.3004 1.6074 3.2920 <.0001
Diabetes
n=239 patients with diabetes
1.0454 0.8025 1.3617 0.7421
Specialty. IM vs. FM
n=478 patients of IM
n=656 patients of FM
0.8538 0.5720 1.2745 0.4394
Specialty: PA/NP vs. FM
n=240 patients of PA/NP
1.1438 0.7559 1.7306 0.5249
Specialty: Peds vs. FM
n=343 patients of Peds
1.5283 0.9198 2.5395 0.1016
ICD-9 of 680.x vs. 681.x-682.x
n=173 patients with a 680.x diagnosis
1.7128 0.9698 3.0250 0.0637

Key: MCNT = Medical Clinic of North Texas, IM = internal medicine, FM = family medicine, PA = physician assistant, NP = nurse practitioner, Peds = pediatrics, ICD-9 = International Classification of Diseases-9.

Table 16. Among 681.x-682.x cases, odds ratios for prescribed antibiotics and prescribed MRSA-covering antibiotics

  Antibiotics MRSA-Covering Antibiotics
Effect Odds Ratio 95% Wald Confidence Limits p Value Odds Ratio 95% Wald Confidence Limits p Value
Intervention period Monthly change 1.122 1.071 1.175 <.0001 1.126 1.056 1.201 <0.001
Historical period Monthly change 1.050 1.024 1.076 0.0001 1.0438 1.008 1.079 0.014
Child or adolescent (age<18) 1.133 0.904 1.421 0.275 0.784 0.551 1.116 0.178
Male 1.099 0.976 1.237 0.116 1.143 0.973 1.342 0.102
Previous case of MRSA 0.876 0.698 1.099 0.253 0.835 0.614 1.135 0.251
Texas clinics patient 2.972 2.274 3.884 <.0001 4.034 2.735 5.950 <.0001
Diabetes 0.895 0.736 1.089 0.2704 0.886 0.691 1.136 0.343
Specialty. IM vs FM 0.866 0.610 1.230 0.422 0.693 0.442 1.088 0.111
Specialty: PA/NP vs FM 1.060 0.632 1.775 0.826 0.936 0.546 1.604 0.810
Specialty: Peds vs FM 1.171 0.828 1.656 0.371 1.770 1.096 2.859 0.020

Key: IM = internal medicine, FM = family medicine, PA = physician assistant, NP = nurse practitioner, Peds = pediatrics.

Some other associations regarding clinicians include that pediatricians were more likely to cover MRSA, midlevels were more likely to obtain a culture, and providers at MCNT were more likely to prescribe antibiotics and more likely to cover MRSA when antibiotics were prescribed. Male patients were twice as likely to have drainage procedures done and were also twice as likely to get cultures done. Patients with diabetes were less likely to have antibiotics prescribed (680.x, cases only).

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Page last reviewed October 2014
Internet Citation: Results (continued). October 2014. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/research/findings/final-reports/mrsa/colorado_mrsa2.html