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

Final Contract Report

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)

 MCNTWHACombined
 PreInterventionp ValuePreInterventionp ValuePreInterventionp Value
Total cases (n)11846 175102 293148 
Procedures (n)22 285 307 
Procedures (%)1.694.350.322516.094.90.0060 10.274.730.0488
Culture (n)213 2918 5021 
Culture (%)17.86.520.066516.6717.650.818117.1214.190.4378

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

 MCNTWHACombined
Pre-intervention91/139 (65.5%)69/106 (65.1%)160/245 (65.3%)
Intervention12/21 (57.1%)36/50 (72.0%)48/71 (67.6%)
All time periods103/161(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

 MCNTWHACombined
 Pre-IntervensionInterventionp ValuePre-InterventionInterventionp ValuePre-InterventionInterventionp Value
Total number of 680.x cases (n)11846 175102 293148 
Antibiotics prescribed (n)6332 4437 10769 
Antibiotics prescribed (%)53.3969.570.059425.1436.270.049536.5246.62<.0001
MRSA-covering antibiotics (n)3418 914 4332 
MRSA-covering antibiotics (%)53.9756.250.832820.4537.840.083940.1946.380.4175

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

 MCNTWHACombined
 Pre-0 InterventionInterventionp ValuePre-InterventionInterventionp ValuePre-InterventionInterventionp Value
Total number of 681.x-682.x cases1752597 1067661 28191258 
Antibiotics prescribed (n)738368 265202 1003570 
Antibiotics prescribed (%)42.1261.64<.000124.8430.560.009235.5845.31<.0001
MRSA-covering antibiotics (n)289166 4956 338222 
MRSA-covering antibiotics (%)39.1645.11.058218.4927.720.017933.738.950.0366

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

 MCNTWHACombined
 Pre-InterventionInterventionp ValuePre-InterventionInterventionp ValuePre-InterventionInterventionp Value
Total number of cases1870643 1240802 31101447 
Antibiotics prescribed (n)801400 309239 1110639 
Antibiotics prescribed (%)42.8362.21<.000124.8831.32<.001735.6745.45<.0001
MRSA-covering antibiotics (n)323184 5870 381254 
MRSA-covering antibiotics (%)40.3246.060518.7729.290.003934.3239.750.0231

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

EffectOdds Ratio95% Confidence Limitsp Value
Intervention period
n=148 cases that were in intervention period
0.36420.11241.17960.0921
Child or adolescent
n=144 children/adolescents
3.17411.007110.00350.0486
Male
n=191 males
2.23391.28973.86920.0041
Previous case of MRSA
n=86 with a previous case
0.72310.34651.5090.3877
MCNT patient
n=164 from MCNT
0.38780.0951.58360.187
Diabetes
n=60 with diabetes
2.38390.77377.34550.1303
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
0.71220.17032.97850.642
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
0.23230.04511.19570.0808
Specialty: Peds vs. FM
n=131 patients of Peds
0.6150.15312.47020.4932

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

EffectOdds Ratio95% Confidence Limitsp Value
Intervention period
n=148 cases that were in intervention period
0.93540.52551.6650.8204
Child or adolescent
n=144 children/adolescents
1.94680.71965.26720.1896
Male
n=191 males
1.84851.10973.07930.0183
Previous case of MRSA
n=86 with a previous case
0.56920.32351.00150.0506
MCNT patient
n=164 from MCNT
0.55630.23731.3040.1772
Diabetes
n=60 with diabetes
1.24380.57562.6880.5789
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
2.2060.55358.79180.2621
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
8.98552.163237.32450.0025
Specialty: Peds vs. FM
n=131 patients of Peds
2.42390.57510.21870.2278

Antibiotics

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

EffectOdds Ratio95% Confidence Limitsp Value
Intervention period
n=148 cases that were in intervention period
2.1831.44293.30260.0002
Child or adolescent
n=144 children/adolescents
0.36280.14880.88460.0258
Male
n=191 males
1.03330.68211.56510.8773
Previous case of MRSA
n=86 with a previous case
0.80140.43271.4840.4812
MCNT patient
n=164 from MCNT
2.73451.56674.77260.0004
Diabetes
n=60 with diabetes
0.55320.3230.94770.0311
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
0.65850.37861.14510.1389
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
1.60380.6963.69570.2674
Specialty: Peds vs. FM
n=131 patients of Peds
2.5971.0286.5590.0436

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

EffectOdds Ratio95% Confidence Limitsp Value
Intervention
n=1,406 cases that were in intervention period
1.78061.49212.1248<.0001
Child or adolescent (age<18)
n=1,105 children/adolescents
1.05570.85391.30510.6168
Male
n=815 males
1.10090.98511.23020.0899
Previous case of MRSA
n=708 with a previous case
0.92870.76091.13360.4672
MCNT patient
n=2,513 patients from MCNT
3.08092.40683.9438<.0001
Diabetes
n=767 patients with diabetes
0.85950.71451.03390.1083
Specialty. IM vs. FM
n=1,483 patients of IM
n=1,637 patients of FM
0.85860.61091.20670.3801
Specialty: PA/NP vs. FM
n=522 patients of PA/NP
1.08490.66061.78180.7474
Specialty: Peds vs. FM
n=815 patients of Peds
1.26640.92081.74160.1464
ICD-9 of 680.x vs. 681.x-682.x
n=441 patients with a 680.x diagnosis
1.02790.80411.31400.8260

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

EffectOdds Ratio95% Confidence Limitsp Value
Intervention period
n=148 cases that were in intervention period
2.62411.49554.60440.0008
Child or adolescent
n=144 children/adolescents
1.14170.58032.24620.701
Male
n=191 males
1.27340.72522.2360.4002
Previous case of MRSA
n=86 with a previous case
1.1650.46932.89210.742
MCNT patient
n=164 from MCNT
4.29182.28368.0662<.0001
Diabetes
n=60 with diabetes
0.92620.44551.92550.8373
Specialty. IM vs. FM:
n=82 patients of FM
n=139 patients of IM
2.7620.98847.71780.0527
Specialty: PA/NP vs. FM
n=84 patients of PA/NP
6.5092.41617.540.0002
Specialty: Peds vs. FM
n=131 patients of Peds
2.4590.7338.2450.1449

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

EffectOdds Ratio95% Confidence LimitspValue
Intervention
n=1,406 cases that were in intervention period
1.93521.53212.4444<.0001
Child or adolescent(age<18)
n=1,105 children/adolescents
0.82700.59861.14260.2495
Male
n=815 males
1.16150.99601.35450.0563
Previous case of MRSA
n=708 with a previous case
0.92180.69811.21700.5656
MCNT patient
n=2,513 patients from MCNT
4.40093.07936.2899<.0001
Diabetes
n=767 patients with diabetes
0.88470.69611.12430.3164
Specialty. IM vs. FM
n=1,483 patients of IM
n=1,637 patients of FM
0.76040.49391.17080.2136
Specialty: PA/NP vs. FM
n=522 patients of PA/NP
1.21270.77511.89740.3984
Specialty: Peds vs. FM
n=815 patients of Peds
1.79641.15682.78960.0091
ICD-9 of 680.x vs. 681.x-682.x
n=441 patients with a 680.x diagnosis
1.59350.98372.58110.0583

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

EffectOdds Ratio95% Confidence Limitsp Value
Intervention
n=626 cases that were in intervention period
1.41081.08031.84250.0115
Child or adolescent (age<18)
n=452 children/adolescents
0.71690.49111.04660.0847
Male
n=815 males
1.12530.91441.38470.2649
Previous case of MRSA
n=271 with a previous case
1.01320.74441.37900.9336
MCNT patient
n=1,173 patients from MCNT
2.30041.60743.2920<.0001
Diabetes
n=239 patients with diabetes
1.04540.80251.36170.7421
Specialty. IM vs. FM
n=478 patients of IM
n=656 patients of FM
0.85380.57201.27450.4394
Specialty: PA/NP vs. FM
n=240 patients of PA/NP
1.14380.75591.73060.5249
Specialty: Peds vs. FM
n=343 patients of Peds
1.52830.91982.53950.1016
ICD-9 of 680.x vs. 681.x-682.x
n=173 patients with a 680.x diagnosis
1.71280.96983.02500.0637

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

 AntibioticsMRSA-Covering Antibiotics
EffectOdds Ratio95% Wald Confidence Limitsp ValueOdds Ratio95% Wald Confidence Limitsp Value
Intervention period Monthly change1.1221.0711.175<.00011.1261.0561.201<0.001
Historical period Monthly change1.0501.0241.0760.00011.04381.0081.0790.014
Child or adolescent (age<18)1.1330.9041.4210.2750.7840.5511.1160.178
Male1.0990.9761.2370.1161.1430.9731.3420.102
Previous case of MRSA0.8760.6981.0990.2530.8350.6141.1350.251
Texas clinics patient2.9722.2743.884<.00014.0342.7355.950<.0001
Diabetes0.8950.7361.0890.27040.8860.6911.1360.343
Specialty. IM vs FM0.8660.6101.2300.4220.6930.4421.0880.111
Specialty: PA/NP vs FM1.0600.6321.7750.8260.9360.5461.6040.810
Specialty: Peds vs FM1.1710.8281.6560.3711.7701.0962.8590.020

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 March 2011
Internet Citation: Management by Primary Care Clinicians of Patients Suspected of Having Community-Acquired Methicillin-Resistant Staphylococcus Aureus Infections: Final Contract Report. March 2011. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/research/findings/final-reports/mrsa/colorado_mrsa2.html