All Purulence Is Local

Epidemiology and Management of Skin and Soft Tissue Infections in Three Urban Emergency Departments

Chris Merritt; John P Haran; Jacob Mintzer; Joseph Stricker; Roland C Merchant

BMC Emerg Med. 2013;13(26)

Conclusion

Staphylococcus aureus is the predominant pathogen in community-acquired purulent SSTIs in the ED, and most patients evaluated for these infections received antibiotics even after I&D. Although antibiotic use, including multi-drug "double coverage", remained common in the sample studied, empiric antibiotics used varied widely, and were poorly targeted toward the causative organisms, all of which represents an opportunity to reduce antibiotic overuse. Local epidemiologic data is critical to the decision-making of ED clinicians, and laboratories should consider reporting disease-specific antibiograms. Future efforts to identify SSTIs in which antibiotic use, particularly anti-MRSA therapy, is indicated could further reduce antibiotic overuse and improve antibiotic stewardship.

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Authors' contributions
CM conceived of the study, and participated in and oversaw its design and coordination. JPH participated in data collection and made significant contributions to analysis and manuscript review. JM and JS were instrumental in design of data collection instruments and data abstraction and data management. RCM participated in design and conception of the study, and provided guidance throughout its course, from conception through manuscript review. All authors read and approved the final manuscript.

Acknowledgements
The authors wish to thank Miao Tai for invaluable assistance with statistical evaluation during this study.
This research was supported by a grant from the University Emergency Medicine Foundation (Grant # 701–5175).
Portions of this work have been presented at the ACEP Research Forum, San Francisco, October 15, 2011, and the AAP National Conference, Boston, October 14, 2011.

Table 1. Demographic and clinical characteristics of ED patients with community-acquired Skin and Soft-tissue infections (SSTIs) by age group
Demographic and clinical characteristics	Pediatric (age < 18)	Adult (age ≥18)	p-value
	n = 191	n = 745
	%	%	p<
Median age in years (IQR)	7 (0–17)	39 (18–89)	*p < 0.001*
Gender			*p < 0.02*
Male	47.6	57.2
Female	52.4	42.8
Ethnicity/race			*p < 0.001*
White	52.9	67.9
Black	22.0	17.6
Hispanic/Other	25.1	14.5
Health insurance status			*p < 0.001*
Private	36.6	33.4
Governmental	44.5	31.3
Both Private and Governmental	8.9	7.0
Uninsured	10.0	28.3
Infection type			p < 0.001
Abscess	38.3	41.9
Cellulitis	44.0	51.0
Furuncle	0.5	0.5
Carbuncle	0.5	0.0
Ulcer	0.5	0.3
Other	16.2	6.3
Previous assessment for this infection	28.3	25.8	p < 0.5
Previous antibiotic treatment for this infection	20.9	18.2	p < 0.4

IQR = interquartile range.

Table 2. Microbiologic culture results from emergency department (ED) patients with community-acquired skin & soft tissue infections
Culture result	Pediatric n = 70% (% pre-treated)	Adult n = 241% (% pre-treated)
No Growth	7.4	9.6
No Growth	(80)	(25)
Staphylococcus aureus	72.1	52.6
Staphylococcus aureus	(20.4)	(21.8)
MRSA	44.3	31.1
MSSA	27.8	21.5
Group B Streptococcus	1.5	3.8
Group B Streptococcus	(0)	(12.5)
Group A Streptococcus	7.4	1.4
Group A Streptococcus	(0)	(0)
Escherichia coli	0	1.9
Escherichia coli		(0)
Pseudomonas aeruginosa	0	1.4
Pseudomonas aeruginosa		(0)
Klebsiella species	0	0.5
Klebsiella species		(0)
Mixed Skin Flora	3	16.8
Mixed Skin Flora	(0)	(11.4)
Other Mixed Flora^a	0	2.4
Other Mixed Flora^a		(20)
Other	8.6	9.6
Other	(33.3)	(15)

^aIncludes Mixed Oral Flora and Mixed GI Flora.
%Pre-treated depicts the percentage of patients identified as having received prior antibiotic treatment for the infection in question.
MRSA = methicillin-resistant S. aureus, MSSA = methicillin-sensitive S. aureus.

Table 3. Antibiotic Resistance Among *Staphylococcus aureus* Isolated from skin and soft tissue infections (SSTIs) in the emergency department
	MSSA			MRSA
	ED Samples (n = 76; 56 Adult)		Antibiogram (n = 619)	ED Samples (n = 101; 70 Adult)		Antibiogram (n = 473)
Drug	Pediatric% resistant	Adult% resistant	Total% resistant	Pediatric% resistant	Adult% resistant	Total% resistant
Ciprofloxacin	0%	2.9%	14%	19.3%	24.5%	61%
Clindamycin	0%	14.7	NR	9.7%	4.1%	NR
Erythromycin	28.6%	41.2%	39%	87.1%	100%	92%
Gentamicin	0%	0%	0%	0%	0%	1%
Levofloxacin	0%	2.9%	13%	19.3%	22.5%	60%
Moxifloxacin	0%	2.94%	NR	NR	NR	NR
Oxacillin^a	0%	0%	0%	100%	100%	100%
Penicillin	85.7%	82.3%	NR	100%	100%	NR
Tetracycline	14.3%	5.9%	5%	0%	0%	2%
TMP/SMX	35.7%	2.9%	1%	0%	0%	1%
Vancomycin	0%	0%	0%	0%	0%	0%
Inducible Clindamycin Resistance	0%	14.7%	NR	3.2%	4.1%	NR

Bolded pairs achieved statistical significance (p < 0.05) in chi-square analysis.
MSSA =methicillin-sensitive S. aureus; MRSA = methicillin-resistant S. aureus; TMP/SMX = Trimethoprim/Sulfamethoxazole; NR = Not Reported
^Oxacillin resistance defines MRSA vs. MSSA in this clinical laboratory.

Table 4. Empiric antibiotic treatment and targeted organisms in microbiologic culture
A.	Culture results
	Pediatric		Adult
	MRSA%	Other result%	MRSA%	Other result%
Anti-MRSA therapy only	52.6	47.4	34.5	65.5
B
	Culture results
	Pediatric		Adult
	MSSA%	Other result%	MSSA%	Other result%
Anti-MSSA therapy only	37.5	72.5	35	65
C.
	Culture results
	Pediatric			Adult
	MRSA%	MSSA%	Other result%	MRSA%	MSSA%	Other result%
Double Coverage	62.5	37.5	0.0	44.3	21.5	34.2

MSSA =methicillin-sensitive S. aureus; MRSA = methicillin-resistant S. aureus.
NB: Patients (63 pediatric, 189 adult) with skin and soft tissue infections (SSTIs) that were cultured in the ED and who received antibiotics are shown, with pediatric and adult patients considered separately. Tables are separated by empiric therapy given and the culture result targeted. 4A: Patients who were treated with empiric anti-MRSA antibiotics only. 4B: Patients who were treated with empiric anti-MSSA antibiotics only. 4C: Patients who were treated with double coverage (treatment with two or more antibiotics with gram-positive coverage). Anti-MRSA antibiotics include antibiotics typically active against community-acquired (CA-) MRSA: trimethoprim-sulfamethoxazole, tetracycline, doxycycline, clindamycin, rifampin, linezolid or vancomycin. Anti-MSSA antibiotics include anti-staphylococcal antibiotics typically ineffective against CA-MRSA (penicillins, cephalosporins, macrolides, fluoroquinolones).

Table 5. Logistic models to identify factors associated by univariate analysis with coverage of the isolated organism by the antibiotic prescribed (A), treatment with multiple antibiotics ("double coverage") (B), and discordant anti-mrsa therapy (C)
Variable	(A) Coverage of the organism isolated^Δ (n=156) or (95%C.I.)	(B) Double coverage (n = 804) or (95%C.I.)	(C) Discordant anti-mrsa therapy (n = 181) or (95%C.I.)
Age group (adult vs. pediatric)	1.92 (0.78–4.76)	5.60 (3.39–9.25)	1.63 (0.82–3.23)
Infection Location
Hand	Ref.	Ref.	Ref.
Other extremity	1.71 (0.45–6.44)	1.37 (0.87–2.18)	1.16 (0.41–3.25)
Buttock	*******	1.07 (0.55–2.11)	1.00 (0.28–3.54)
Trunk	2.31 (0.5–10.67)	1.00 (0.56–1.78)	0.64 (0.22–1.87)
Head	0.62 (0.1–3.66)	1.15 (0.44–2.96)	4.00 (0.40–39.83)
Face	4.92 (0.49–49.61)	0.95 (0.54–1.68)	0.46 (0.13–1.59)
Genitalia	0.31 (0.02–6.11)	1.07 (0.30–3.81)	0.67 (0.04–12.27)
Multiple Locations	1.23 (0.11–14.42)	1.07 (0.45–2.54)	0.67 (0.08–5.75)
Previous assessment for this infection	1.27 (0.4–4.02)	0.85 (0.60–1.20)	0.86 (0.42–1.79)
Previous antibiotic treatment for this infection	4.13 (0.53–32.28)	0.81 (0.54–1.22)	0.45 (0.19–1.07)
Disposition (hospital admission)	2.78 (1.12–6.89)*	0.99 (0.73–1.35)	0.66 (0.33–1.32)
I&D performed	4.47 (1.71–11.65)*	1.07 (0.77–1.47)	0.87 (0.47–1.60)
Culture performed	N/A	1.37 (1.00–1.87)	N/A
Gender
Male	Ref.	Ref.	Ref.
Female	0.92 (0.38–2.24)	0.75 (0.56–1.00)	0.82 (0.45–1.47)
Ethnicity/race
White	Ref.	Ref.	Ref.
Black	1.58 (0.49–5.05)	0.65 (0.43–0.97)*	0.89 (0.41–1.89)
Hispanic/Other	5.62 (0.71–44.27)	0.72 (0.48–1.09)	1.06 (0.46–2.42)
Health insurance status
Private	Ref.	Ref.	Ref.
Governmental	1.31 (0.41–4.19)	0.94 (0.66–1.34)	0.85 (0.40–1.77)
Both private and Governmental	0.11 (0.02–0.5)*	0.80 (0.45–1.43)	1.94 (0.36–10.50)
None	1.63 (0.44–5.98)	1.23 (0.84–1.81)	0.69 (0.33–1.47)

^Δexcludes cultures with no growth or mixed flora and patients not treated with antibiotics.
* denotes statistically significant result.
*** variable had perfect prediction in the model.
NB: Three univariable logistic models were created to identify demographic or clinical variables associated with (A) coverage of the organism isolated by the empiric ED antibiotic therapy, (B) use of multiple antibiotics as empiric therapy ("double coverage"), and (C) discordance between use of anti-MRSA antibiotics and presence of MRSA as identified by microbiologic culture. In the third regression model, concordance was defined as presence of MRSA in culture when any anti-MRSA treatment was prescribed or presence of MSSA in culture when only anti-MSSA treatment was prescribed.